Colonization Ability Research Articles

Peptidoglycan analysis reveals that synergistic deacetylase activity in vegetative Clostridium difficile impacts the host response

Clostridium difficile is an anaerobic and spore-forming bacterium responsible for 15–25% of postantibiotic diarrhea and 95% of pseudomembranous colitis. Peptidoglycan is a crucial element of the bacterial cell wall that is exposed to the host, making it an important target for the innate immune system. The C. difficile peptidoglycan is largely N-deacetylated on its glucosamine (93% of muropeptides) through the activity of enzymes known as N-deacetylases, and this N-deacetylation modulates host–pathogen interactions, such as resistance to the bacteriolytic activity of lysozyme, virulence, and host innate immune responses. C. difficile genome analysis showed that 12 genes potentially encode N-deacetylases; however, which of these N-deacetylases are involved in peptidoglycan N-deacetylation remains unknown. Here, we report the enzymes responsible for peptidoglycan N-deacetylation and their respective regulation. Through peptidoglycan analysis of several mutants, we found that the N-deacetylases PdaV and PgdA act in synergy. Together they are responsible for the high level of peptidoglycan N-deacetylation in C. difficile and the consequent resistance to lysozyme. We also characterized a third enzyme, PgdB, as a glucosamine N-deacetylase. However, its impact on N-deacetylation and lysozyme resistance is limited, and its physiological role remains to be dissected. Finally, given the influence of peptidoglycan N-deacetylation on host defense against pathogens, we investigated the virulence and colonization ability of the mutants. Unlike what has been shown in other pathogenic bacteria, a lack of N-deacetylation in C. difficile is not linked to a decrease in virulence.

Vulpia myuros, an increasing threat for agriculture

AbstractVulpia myuros is an annual grass species of Mediterranean origin, which has achieved a global distribution. It is a fast‐growing species, with high colonisation and competitive abilities. This species is considered an invasive weed in most countries where it has been introduced, with highly negative economic impact where it now dominates. It is increasingly found to be a problematic weed in winter cereals, especially in no‐till and reduced tillage systems, across Europe, United States and Australia. Seeds of V. myuros have reduced germination potential when buried. However, where tillage interventions are reduced, ideal conditions for V. myuros are created. Minimum and no tillage practices are increasing worldwide, with a concomitant increase in the spread and abundance of V. myuros. Effectiveness of herbicides is mostly suboptimal, in particular for well‐established populations forming dense swards, even though no herbicide resistance has yet been identified. An integrated management approach, increasing crop diversification combined with management adaptations, possibly including herbicides is suggested as an effective control strategy. Despite increasing research on V. myuros, more information is needed to optimise the management of this weed. Based on the species’ Mediterranean origins and adaptation to warm and dry environments, an increase of its global importance may be expected with climate changes. It is thus paramount to increase the awareness around this species, improve its identification in the field and monitor its spread before it becomes a concern of similar magnitude to grass weeds like Alopecurus myosuroides or Lolium rigidum.

RcsB-dependent regulation of type VI secretion system in porcine extra-intestinal pathogenic Escherichia coli.

Signal transduction system and specialized secretory devices are crucial for bacteria to sense and adequately adapt in adverse environmental conditions. Therefore, it's crucial for microbes to detect and respond to lethal attacks when envelope is perturbed so as to minimize and fix the damage in milieu. We investigated the adaptive response of porcine extra-intestinal pathogenic Escherichia coli PCN033 to polymyxin B challenge. Treatment with polymyxin B led to rapid and robust activation of Rcs system via RcsF, as well as the accumulation of reactive oxygen species. ExPEC T6SS expression was strongly induced by RcsB in Rcs system, resulting in the reduction in the damage to constitute a survival strategy. Finally, we show that T6SS of ExPEC is involved in its pathogenicity in mouse model. Compared with the wild type strain, the deletion of T6SS genes led to a decrease in the organ colonization ability, and the RcsFS2DM3Q mutant that caused Rcs activation had a stronger colonization ability than the wild type strain. In conclusion, Rcs system orchestrates Rcs cascade to trigger antioxidant defense of T6SS, and presents a typical model in which a bacterium reschedule its transcription network via the Rcs phosphorelay pathway in response to membrane perturbations for survival and pathogenesis.

Exopolysaccharides and indole-3-acetic acid producing Bacillus safensis strain FN13 potential candidate for phytostabilization of heavy metals

Microbial population of soils irrigated with industrial wastewater may contain certain exopolysaccharides (EPS) and indole-3-acetic acid (IAA) producing bacterial strains having the ability to tolerate heavy metals along with plant growth-promoting (PGP) traits. As cadmium is one of the most toxic heavy metals for soils, plants, animals, and human beings, the present study was planned to isolate and characterize EPS- and IAA-producing, Cd-tolerant bacterial strains having tolerance against heavy metals along with plant growth-promoting traits. A total of 30 rhizobacterial strains (FN1-FN30) were isolated from rhizosphere soil collected from fields around industrial areas and roadsides irrigated with industrial wastewater. Out of these, eight isolates with the combined ability of IAA production and EPS production were characterized for PGP traits. On the basis of multifarious PGP traits and the results of root colonization assay, three most efficient EPS- and IAA-producing, Cd-tolerant plant growth-promoting strains, i.e., FN13, FN14, and FN16, were selected for multiple metal (Cd, Pb, Ni, and Cu) tolerance test along with quantification of growth, and IAA and EPS production abilities under Cd stress. Increasing levels of Cd stress negatively affected the tested characteristics of these strains, but FN13 showed more stability in growth, IAA production (18.24 μg mL-1), and EPS production (148.99 μg mL-1) compared to other strains under Cd stress. The morphological and biochemical analysis confirmed FN13 as Gram-positive, rod-shaped bacteria with smooth colonies of yellow appearance. The strain FN13 has strong root colonization (3.36 × 106 CFU g-1) ability for mustard seedlings and can solubilize Zn and phosphate along with the production of HCN, ammonia, and siderophores. The 16S rRNA sequencing confirmed it as the Bacillus safensis strain FN13. It can be explored as potential phytostabilizing biofertilizer for heavy metal-contaminated soils.

Changes in intestinal flora in preeclampsia rats and effects of probiotics on their inflammation and blood pressure.

The aim of this study was to investigate the changes in intestinal flora in preeclampsia rats and the effects of probiotics on their inflammation and blood pressure. A total of 40 Specific Pathogen Free (SPF) Wistar rats were randomly selected in this study. Abdominal operation was performed to reduce uterine blood perfusion, so as to establish the model of preeclampsia in rats. All rats were randomly divided into two groups, namely, observation group (treated with probiotics, n=20) and control group (not treated with probiotics, n=20). Subsequently, the changes in serum endotoxin level during intervention, the 24-h urinary 99mTc-diethylene triamine pentaacetic acid (DTPA) excretion rate, and intestinal flora colonization ability after intervention were compared between the two groups. The distribution of intestinal flora after intervention was recorded in the two groups. Meanwhile, vascular endothelial function and blood pressure following intervention were compared between the two groups as well. In addition, the changing trend of inflammatory cytokines during intervention in the two groups, and the correlation of colonization ability of intestinal flora with changes in systolic blood pressure and high-sensitivity C-reactive protein (hs-CRP) level in patients were analyzed. At 3 days and 1 week after intervention, serum endotoxin level in the observation group was significantly lower than that in the control group at the same period (p<0.05). Following intervention, observation group exhibited remarkably higher excretion rate of 24-h urinary 99mTc-DTPA (p<0.05), stronger colonization ability of intestinal flora (p<0.05), higher levels of Bifidobacteria and Lactobacillus in intestinal flora (p<0.05), lower level of endothelin-1 (ET-1) (p<0.05) and higher level of nitric oxide (NO) (p<0.05) than the control group. In addition, the systolic blood pressure and diastolic blood pressure in the observation group were basically normal, which were both notably lower than those in the control group (p<0.05). At 3 days and 1 week after intervention, the levels of serum inflammatory cytokine hs-CRP in the observation group was markedly lower than that in the control group (p<0.05) at the same period. Furthermore, the colonization ability of intestinal flora was negatively associated with the changes in systolic blood pressure and hs-CRP level in patients (p<0.05). Treating preeclampsia rats with probiotics can effectively reduce the level of serum endotoxin, improve the body's capacity to eliminate metabolites and the colonization ability of intestinal flora, maintain the stability of intestinal flora, enhance vascular endothelial function, and reduce blood pressure and the body's inflammatory responses.

Functional characterization of asnC family transcriptional regulator in Pseudomonas aeruginosa PGPR2 during root colonization

Transcriptional regulators in bacteria are the crucial players in mediating communication between environmental cues and DNA transcription through a complex network process. Pseudomonas aeruginosa PGPR2 is an efficient root colonizer and a biocontrol strain. Previously, we identified that the transcriptional regulator, asnC, negatively regulates the corn root colonization of P. aeruginosa PGPR2. In a transposon insertion sequencing (INSeq) screen, the asnC insertion mutant was positively selected during root colonization, meaning the disruption of asnC improves the fitness of the P. aeruginosa PGPR2 strain for the root colonization. In this study, we constructed isogenic mutant of asnC family transcriptional regulator encoded by PGPR2_17510 by allele exchange mutagenesis. The ΔasnC mutant was able to efficiently colonize corn roots with a twofold increase in population when compared to the wild-type strain. Similarly, the mutant strain outcompeted the wild-type strain in a competition assay, where the mutant strain represented 90% of the total population recovered from the root. We compared the whole transcriptome of the wild-type and the ΔasnC mutant of P. aeruginosa PGPR2 when exposed to the corn root exudates. The RNA-Seq revealed that a total of 360 genes were differentially expressed in the ΔasnC strain of P. aeruginosa PGPR2. Inactivation of asnC transcriptional regulator resulted in the up-regulation of several genetic factors implicated in metabolism, uptake of nutrients, motility, stress response, and signal transduction, which could play crucial roles in root colonization. This notion was further validated by phenotypic characterization and quantification of transcription pattern of selected genes associated with metabolism, motility, and carbon catabolite repression between wild type and mutant strain, which was in agreement with transcriptome data. Similarly, ΔasnC strain formed increased biofilm on abiotic surface validating our RNA-seq analysis, where transcript levels of several genes associated with biofilm formation were up-regulated in the mutant strain. We report that the inactivation of an asnC family transcriptional regulator encoded by PGPR2_17510 enhances the root colonization and biofilm-forming ability of P. aeruginosa PGPR2. Together, our results provide evidence for the molecular adaptations that enable ΔasnC mutant strain to colonize on the corn roots and to form a biofilm.

Correlations between inflammatory response, oxidative stress, intestinal pathological damage and intestinal flora variation in rats with type 2 diabetes mellitus.

To explore the correlations between inflammatory response, oxidative stress, intestinal pathological damage, and intestinal flora variation in rats with type 2 diabetes mellitus (T2DM). A total of 80 specific pathogen-free (SPF) male Sprague-Dawley (SD) rats purchased from Beijing Vital River Laboratory Animal Technology Co., Ltd. (Beijiing, China) were randomly divided into two groups, namely T2DM group (n=40) and normal group (n=40). Then, the contents of inflammatory factors [high-sensitivity C-reactive protein (hs-CRP) and tumor necrosis factor-α (TNF-α)] and oxidative stress indicators [malondialdehyde (MDA) and superoxide dismutase (SOD)] were detected. Meanwhile, the distributions of intestinal florae Bifidobacteria, Escherichia coli, Lactobacilli and Enterococcocci and the variation of endotoxin were compared between the two groups. Besides, colon specimens were pathologically examined to observe the occurrence of chronic inflammation variation, intestinal mucosal erosion, intestinal mucosal wall thickening and intestinal mucosal fibrosis. Next, the influences of the glycosylated hemoglobin on levels of hs-CRP, MDA and endotoxin and colonization ability of intestinal florae were analyzed. Additionally, univariate and multivariate analyses were performed for underlying the relations of the pathogenesis of T2DM in rats with their inflammatory response, antioxidant capacity, endotoxin level and intestinal flora colonization capacity. The levels of hs-CRP and TNF-α were significantly higher in T2DM group than those in normal group (p<0.05). T2DM group exhibited an overtly elevated MDA level (p<0.05), and a clearly lowered SOD level (p<0.05) in comparison with normal group. As to intestinal flora-related indicators, the levels of endotoxin, Escherichia coli and Enterococcocci were evidently higher in T2DM group than those in the normal group (p<0.05), while the levels of Bifidobacteria and Lactobacilli in T2DM group were remarkably lowered (p<0.05). Pathological lesions, including chronic inflammation variation, mucosal erosion, mucosal wall thickening and mucosal fibrosis in intestinal mucosal tissues, were worse in T2DM group than those in the normal group (p<0.05). In T2DM rats, the level of glycosylated hemoglobin was positively correlated with changes in the levels of hs-CRP, MDA and endotoxin (p<0.05), and negatively associated with changes in colonization ability of intestinal florae (p<0.05). Aggravated inflammatory response, decreased antioxidant capacity, increased endotoxin level and weakened colonization ability of intestinal florae were independent risk factors for T2DM in rats. Rats with T2DM have significantly aggravated inflammatory response, weakened antioxidant capacity, imbalanced intestinal florae and markedly pathological changes of intestinal mucosa.

Ability of plant species to colonise human‐disturbed habitats: Role of phylogeny and functional traits

AbstractQuestionWhich species are successful colonisers of disturbed sites; species adapted to seed dispersal, resistance to abiotic stress, or competition ability? Are successful adaptations for colonisation shared by phylogenetically related species?LocationCzech Republic, Central Europe.MethodsWe used two indices of plant species’ colonisation ability (developed from an extensive dataset of dated successional series for 1,531 plant species of the Czech Republic): index of colonisation potential (ICP), which is corrected for mass effect (species’ frequency in the landscape acquired from Czech National Phytosociological Database, accounting for more common colonisation events of frequent species), and index of colonisation success (ICS), which is solely based on actual species frequencies in disturbed habitats. We also used preferences for successional age (median of age of sites that species had colonised). We correlated these indices with plant functional traits for three functional groups (woody species, non‐woody perennial polycarpic, and non‐woody monocarpic species) either considering the phylogenetic history of a species or not.ResultsWoody species were the best colonisers and had the highest preferences for late‐successional stages. Non‐woody monocarpic species had a higher ICP than polycarpic species while their ICS were comparable. The best predictor of colonisation ability of both monocarpic and polycarpic non‐woody species was canopy height, indicating importance of competition. Other successful colonisers were species with seed traits promoting dispersal (low seed mass or low seed terminal velocity). We did not find traits suitable for adverse biotic conditions (high specific leaf area, SLA), low canopy height) to be important. Successional age preference of species was indicated mainly by seed traits (seed mass, seed longevity), which highly corresponded with species’ phylogenetic history.ConclusionsColonisation of disturbed sites is limited by seed dispersal and competitive interactions rather than an adverse abiotic environment.

Transcriptional Regulator YqeI, Locating at ETT2 Locus, Affects the Pathogenicity of Avian Pathogenic Escherichia coli.

Simple SummaryAvian pathogenic Escherichia coli (APEC) is the causative agent of colibacillosis, threatening the development of the poultry industry. The study on APEC’s pathogenic mechanism is of great importance. In this study, we investigated the role of YqeI, a transcriptional regulator locating at E. coli type three secretion system 2 in APEC. The transcriptional results revealed that YqeI affected the expression of the genes involving in bacterial localization, locomotion and biological adhesion. A series experiments also demonstrated that the absence of yqeI decreased the bacterial flagella formation ability, motility ability, antiserum bactericidal ability, adhesion ability and colonization ability. Our data suggested that the transcriptional regulator YqeI indeed participates in the pathogenicity of APEC.Avian pathogenic Escherichia coli (APEC) is the leading cause of systemic infections in poultry worldwide and has a hidden threat to public health. Escherichia coli type three secretion system 2 (ETT2), similar to the Salmonella pathogenicity island SPI1, is widely distributed in APEC and associated with virulence. The function of YqeI, which is one of the hypothetical transcriptional regulators locating at the ETT2 locus of APEC, is unknown. In this study, we successfully obtained the mutant strain AE81ΔyqeI of the wild type strain AE81 and performed the transcriptional profiling assays. Additionally, the transcriptional sequencing results revealed that YqeI influenced localization, locomotion and biological adhesion and so on. The transmission electron microscope observation showed that the wild type strain AE81 possessed long curved flagella, whereas the mutant strain AE81ΔyqeI hardly had any. The strain AE81ΔyqeI exhibited lower motility than AE81 after culturing the dilute bacterial suspension on a semisolid medium. It was also found that the survival ability of AE81ΔyqeI weakened significantly when AE81ΔyqeI was cultured with 0%, 10%, 20%, 30%, 40% and 50% SPF serum in PBS, and AE81ΔyqeI had decreased adherence to DF-1 cells compared with AE81 in the bacterial adhesion assay. The bacterial colonization assay indicated that the virulence of AE81ΔyqeI was reduced in the heart, liver, spleen, and lung. These results confirmed that the transcription regulator YqeI is involved in APEC’s pathogenicity, and this study provides clues for future research.

Using a Multi-Century Post-Fire Chronosequence to Develop Criteria to Distinguish Prior and Bowman’s (2020) Post-Fire Obligate Coloniser and Fire-Intolerant Flora

Prior and Bowman added a new dimension to existing frameworks of post-fire responses of woody plants, by including the trait of colonisation ability (C) for those taxa which neither resprout (Rf−) nor produce seedlings (Sf−) after fire. Specifically, they recognised distinctions between: (i) post-fire obligate colonisers, being species that neither resprout nor produce seedlings from persistent seed banks post-fire but are able to colonise burnt areas through dispersal from unburnt populations, and (ii) fire-intolerant, which are unable to recover after fire by either resprouting, seeding or colonisation. We use data on temporal and spatial patterns of colonisation of Rf−Sf− mistletoes from a chronosequence study with an exceptionally long span of times since fire as a practical example of the delineation of post-fire obligate coloniser and fire-intolerant species. We propose that when a population of a species is burnt, if the species is unable to regularly colonise and reach reproductive maturity in burnt areas spatially distant from fire edges within plausible and regularly-occurring maximum fire-return intervals for the now-burnt community type, it would be classified as fire-intolerant. In our examples, Lysiana meets the criteria for fire-intolerant in obligate-seeder eucalypt woodland, while Amyema is classed as a post-fire obligate coloniser.

Bacteriophages as sources of small non-coding RNA molecules

Bacteriophages play an essential role in the transferring of genes that contribute to the bacterial virulence and whose products are dangerous to human health. Interestingly, phages carrying virulence genes are mostly temperate and in contrast to lytic phages undergo both lysogenic and lytic cycles. Importantly, expression of the majority of phage genes and subsequent production of phage encoded proteins is suppressed during lysogeny. The expression of the majority of phage genes is tightly linked to lytic development. Among others, small non-coding RNAs (sRNAs) of phage origin are involved in the regulation of phage gene expression and thus play an important role in both phage and host development. In the case of bacteria, sRNAs affect processes such as virulence, colonization ability, motility and cell growth or death. In turn, in the case of phages, they play essential roles during the early stage of infection, maintaining the state of lysogeny and silencing the expression of late structural genes, thereby regulating the transition between phage life cycles. Interestingly, sRNAs have been identified in both lytic and temperate phages and they have been discussed in this work according to this classification. Particular attention was paid to viral sRNAs resembling eukaryotic microRNAs.

Enhanced recruitment and hematopoietic reconstitution of bone marrow-derived mesenchymal stem cells in bone marrow failure by the SDF-1/CXCR4.

Aplastic anemia (AA) is a bone marrow failure disease. It is difficult to treat AA, and in addition, relapses are common because of its complex disease pathogenesis. Allogeneic bone marrow-derived mesenchymal stem cells (BMSCs) infusion is an effective and safe treatment option for the AA patients. However, it found that BMSCs infusion in AA patients is less than 30% effective. Therefore, the key to improve the efficacy of BMSCs treatment in these patients is to enhance their homing efficiency to the target sites. Studies have shown that stromal cell-derived factor-1 (SDF-1)/CXC chemokine receptor 4 (CXCR4) axis plays an important role in promoting BMSCs homing. In this study, human BMSCs were transduced with lentivirus stably expressing CXCR4-BMSCs. Transduced BMSCs resemble normal BMSCs in many ways. Migration ability of CXCR4-BMSCs toward SDF-1 was increased because of the overexpression of CXCR4. In the mice with bone marrow failure, the migration and colonization ability of CXCR4-BMSCs to the bone marrow was significantly improved as seen by IVIS imaging and FACS. The SDF-1 level in the bone marrow failure mice was significantly higher than in the normal mice. Thus, from our study, it is clear that after CXCR4-BMSCs were infused into mice with bone marrow failure, SDF-1 interacted with CXCR4 receptor, leading cells to migrate and colonize to bone marrow. Because of the high SDF-1 expression in mouse bone marrow and CXCR4 receptor expression in cells, BMSCs homing was increased.

A strategy for enhanced tumor targeting of photodynamic therapy based on Escherichia coli-driven drug delivery system

Escherichia coli (E. coli) DH5α has been recognized as a non-pathogenic bacterial strain with tumor colonization ability. However, whether such a bacteria-driven drug-delivery system can improve the targeting of tumor therapy or not remains essentially untouched. Herein, a series of zinc phthalocyanine (ZnPc) photosensitizers with different numbers of charges were prepared and their electrostatic adhesion properties on E. coli were investigated via measuring their fluorescence intensities by flow cytometer. Among these ZnPc photosensitizers investigated, the ZnPc conjugate with four positive charges (named ZnPc-IR710) exhibited the highest loading capacity and the best fluorescence imaging performance of E. coli. With the help of E. coli, E. coli@ZnPc-IR710 presented a significantly enhanced cytotoxicity on human breast cancer MCF-7 cells compared with ZnPc-IR710 (survival rate of tumor cells was 39% vs. 57% at a concentration of 50 nmol L−1). Moreover, in vivo study showed that E. coli@ZnPc-IR710 remarkably inhibited the tumor growth and resulted in a complete tumor growth suppress in subcutaneous mouse 4T1 breast tumor model. These results demonstrated the great promise of bacterial-guided photodynamic therapy (PDT) in the treatment of solid tumors, and provide a unique strategy to enhance the antitumor efficacy of PDT by utilizing bacterial vectors in tumors.

Biological effects of root exudates from resistant and susceptible banana varieties on Fusaiurm oxysporum f. sp. cubense and Bacillus subtilis

Root exudates of banana resistant variety ('Nantianhuang') and susceptible variety ('Guijiao No. 6') to Fusarium wilt were collected in vitro by bathing root system to examine the biological effects of root exudates from banana varieties on Fusaiurm oxysporum f. sp. cubense and Bacillus subtilis. We explored the effects of root exudates of different banana varieties on the abundance of soil microorganisms and the growth of F. oxysporum f. sp. cubense and B. subtilis. The results showed that root exudates from resistant variety could significantly reduce the abundance of soil fungi and inhibit the spore germination of F. oxysporum f. sp. cubense. Root exudates from susceptible variety could significantly stimulate mycelia growth and spores germination, whereas root exudates from the tested banana varieties could significantly increase the growth and biofilm formation of B. subtilis. By dealing with the root exudates of resistant and susceptible varieties, the growth rate of mycelia were 11.28 and 12.28 mm·d-1, and the germination rate of spores were 34.6% and 79.5%, respectively. After culturing for 12 h, the growth rates of B. subtilis (OD600) were 1.27 and 1.14, and the biofilm formation (OD570) were 1.11 and 1.30 after static culturing 72 h, respectively. There were significant differences between the values of resistant and susceptible varieties. The colonization amount of B. subtilis in the rhizosphere of susceptible variety was significantly higher than that of resistant variety. The contents of free amino acids and organic acid in root exudates of the resistant variety were higher than that of susceptible variety. The content ratio of acetic acid and proline in the root exudates of resistant variety were 3.7 times and 2.4 times of that of susceptible variety. In conclusion, root exudates of banana resistant variety could inhibit the growth of F. oxysporum f. sp. cubense. Root exudates from susceptible variety could promote the growth of F. oxysporum f. sp. cubense,while that from the tested banana varieties could all significantly enhance growth, biofilm formation and colonization ability of B. subtilis.

Prophage phiv205-1 facilitates biofilm formation and pathogenicity of avian pathogenic Escherichia coli strain DE205B

Avian colibacillosis caused by avian pathogenic Escherichia coli (APEC) causes significant economic losses to the poultry industry worldwide and is also a leading potential threat to human health. Bacteriophages integrate into the host bacterial chromosome, and are an important source of genetic variation and have a major impact on bacterial evolution. Previously, we predicted prophage phiv205-1 in APEC strain DE205B. Here, to determine the function of prophage phiv205-1, we constructed the prophage deletion mutant DE205BΔphiv205-1. Compared with the wild-type (WT) APEC strain DE205B, the adherence and invasive abilities of DE205BΔphiv205-1 were reduced by 41.88 %(P < 0.05). Further, the mutant strain had 52.38 % reduced biofilm formation compared with the WT strain (P < 0.001). Chick challenge showed that the median lethal dose (LD50) of the mutant strain and WT strain was 3.13 × 105 colony-forming units (CFU) and 3.86 × 104 CFU, respectively, indicating that the mutant strain had decreased virulence compared with the WT strain. Furthermore, in vivo studies showed that, compared with the WT strain, DE205BΔphiv205-1 bacterial loads were reduced by 1.6-fold (P < 0.05) and 4.8-fold (P < 0.001) in the lungs and brains, respectively, of the infected chicks. In conclusion, the prophage phiv205-1 contributes to the virulence of APEC strain DE205B by facilitating the adherence, biofilm formation, and colonization abilities of its host strain.

Role of Biofilm Formation by Bacillus pumilus HR10 in Biocontrol against Pine Seedling Damping-Off Disease Caused by Rhizoctonia solani

The biocontrol process mediated by plant growth-promoting rhizobacteria (PGPR) relies on multiple mechanisms. Biofilm formation plays an important role in the ability of PGPR to control plant diseases. Bacillus pumilus HR10, one such PGPR, promotes the growth of Pinus thunbergii. This study showed that the wild-type strain B. pumilus HR10 produces a stable and mature biofilm in vitro. Biofilm-deficient mutants of B. pumilus HR10 with different phenotypes were screened by mutagenesis. The contents of extracellular polysaccharides (EPS) and proteins produced by the mutant strains were significantly reduced, and the biofilms of the mutants were weakened to varying degrees. The swarming abilities of the wild-type and mutant strains were positively correlated with biofilm formation. A colonization assay demonstrated that B. pumilus HR10 could colonize the roots of Pinus massoniana seedlings in a large population and persist, while biofilm-deficient mutants showed weak colonization ability. Furthermore, a biocontrol assay showed that biocontrol efficacy of the mutants was reduced to a certain degree. We determined the inhibitory activity of B. pumilus HR10 and its ability to induce systemic resistance against Rhizoctonia solani of plants. The synthesis of lipopeptide antibiotics is probably involved in biofilm formation by B. pumilus HR10. These observations not only provide a reference for further research about the coordinated action between biofilm formation and the multiple biocontrol mechanisms of B. pumilus HR10 but also improve the understanding of the regulatory pathway of biofilm formation by B. pumilus HR10.

Sarocladium zeae is a systemic endophyte of wheat and an effective biocontrol agent against Fusarium head blight

Fusarium head blight (FHB) causes severe economic impacts by reducing yield and quality of small grain cereals, and poses health risks to both humans and animals via the accumulation of mycotoxins such as deoxynivalenol (DON). The use of endophytic fungi as potential biological control agents is an underexplored method for reducing the impact of FHB. There are several mechanisms through which endophytic fungi may affect biological control, including the production of antifungal secondary metabolites, resource competition with pathogens, and stimulation of innate plant defense responses. We determined that Sarocladium zeae, a known endophyte of corn that produces secondary metabolites inhibitory to Fusarium graminearum, is also able to colonize wheat extensively. Strains of S. zeae differ in their colonization ability, but S. zeae NRRL 34560 was shown to be a systemic endophyte of wheat, successfully colonizing the majority of internal plant organs and surviving within the plant through its life cycle. When allowed to pre-colonize wheat ahead of inoculation with F. graminearum, this strain significantly reduced FHB symptoms (57.9% reduction in area under the disease progress curve) and DON content in harvested wheat heads (61.2% reduction). While these protective effects may arise from multiple simultaneously acting mechanisms, we demonstrate that plant hormones related to defense signaling respond to the presence of S. zeae, indicating that defense priming may be an important mechanism leading to protection in this system.

Actinomycete Strains Isolated from Saline Soils: Plant-Growth-Promoting Traits and Inoculation Effects on Solanum lycopersicum

Excessive use of chemical products in agriculture is causing significant environmental pollution and the loss of lands and fertility of agricultural soils. Plant-growth-promoting bacteria are a valid alternative strategy for sustainable agriculture. The aim of this study was to select actinomycete strains based on their plant-growth-promoting traits and to investigate their root association abilities and biostimulant effects on Solanum lycopersicum. The strains were investigated for their phosphate solubilization ability, production of indole-3-acetic acid, hydrocyanic acid, and ammonia, and several enzymatic activities. Bacteria–plant-root associations were studied by scanning electron microscopy. A greenhouse experiment was carried out to assess inoculation effects. Of sixty isolates, fourteen strains showed significant plant-growth-promoting traits. All fourteen strains solubilized phosphate, produced ammonia, and showed several enzymatic activities at different rates. The production of indole-3-acetic acid was shown by nine strains, while hydrocyanic acid production was observed in eleven of them. Scanning electron microscopy revealed that strains have good in vitro plant root association and colonization abilities. In planta inoculation by actinomycete strains positively influenced plant growth parameters. The best results were shown by seven actinomycete strains, suggesting their possible utilization as biofertilizer agents for sustainable agriculture.

Exploring the antibacterial mechanism of essential oils by membrane permeability, apoptosis and biofilm formation combination with proteomics analysis against methicillin-resistant staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) is one of the important causes of food poisoning and infectious diseases worldwide, it can produce a large number of virulence factors, enhance the colonization ability of the host so that it can quickly colonize and spread on the surface of the objects. Essential oil (EO) is one of the natural products with antimicrobial properties, can be used as an important source of antibacterial agent discovery, and has a broad development prospect. However, the unclear mechanisms of antibacterial action have become an obstacle to its further development and use. Hence, the objective of the present study was to reveal the antibacterial mechanism of EO from Amomum villosum Lour (A villosum Lour) against MRSA using label-free quantitative proteomics, investigate the effect of EO on the bacterial proteome, enzymatic activities and leakage of bacterial intracellular biomacromolecule. Proteomic analysis of MRSA in the presence of EO found that a total of 144 differential expressed proteins (DEPs) between the control and treatment group, in which 42 proteins were distinctly up-regulated and 102 proteins were down-regulated. Besides, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis, determination of cell membrane permeability and apoptosis, scanning electron microscopy (SEM) observations, bacterial surface hydrophobicity, and biofilm formation measurement were performed. Collectively, the above results indicated that the cell membrane damage by EO leads to the loss of membrane integrity and causes leakage of intracellular macromolecular substances, inhibition of protein, and biofilm synthesis. These findings manifested that EO exerts antibacterial effect by multiple avenues and expands our understanding of the antibacterial mechanism, it has potential application value in food preservative and pharmaceutical industries.

Effects of local characteristics and landscape patterns on plant richness: A multi-scale investigation of multiple dispersal traits

Abstract Plant species distributions are determined by various factors (including the dispersal modes and the complex physical environment) across multiple spatial scales, in which the dispersal distance of different dispersal modes and the external environment (including local characteristics and landscape patterns) are closely related. Therefore, understanding the response mechanism of plant species with different dispersal abilities to environmental factors is critical for developing effective landscape management strategies and prioritizing biodiversity conservation efforts at the appropriate scale. In this study, we aimed to explore: (1) the spatial distribution of plant species richness; (2) the spatial scale at which plant species have the strongest response to environment variables (scale of effect); and (3) to identify the key factors that affect the plant species at local and six landscape scales (a 0.5 km, 1 km, 1.5 km, 2 km, 3 km and 4 km-radius circle) considering multiple dispersal traits. We conducted vegetation surveys at 53 sites and classified plant species into three dispersal modes, including biotic dispersal (BD), abiotic dispersal (AD) and autochorous (AT), based on the respective dispersal vector of the seed. We classified land use types into 15 categories and clipped 6 specified radii around each sampling site using ENVI 5.1 and ArcGIS 10.3 software. We applied linear mixed effects models (LMM) to analyze the local and the surrounding landscape variables in predicting plant species richness in Qingshui town of Beijing, China. Our results revealed that the response traits of species to environment factors varied across different scales, proving the existence of scale effect in our study area. The biotically-dispersed (BD) and abiotically-dispersed (AD) species favored structurally complex habitats with greater tree height and cover of herb at the local scale. The area-weighted mean of shape metric (SHAPE_MN) of shrubbery and the euclidean nearest neighbor distance distribution (ENN_AM) of bare land play a major role in determining BD and AD species at large spatial extents, which suggest that the patterns and ecological attributes of patches of these two land use types hinder the migration and colonization ability of species and thus affect the species richness. These results suggest that a multi-scale approach should be encouraged to help guide effective landscape managements in conserving biodiversity for different response traits.