Colonization Ability Research Articles

Biocontrol efficacy of Burkholderia pyrrocinia S17-377 in controlling rice sheath blight

Rice sheath blight, caused by Rhizoctonia solani, is a major disease of rice that significantly affects rice production. To find sustainable and effective methods to control this disease, biocontrol strains have emerged as a promising solution. In this study, a total of 28 strains were screened from the rhizosphere of rice plants in order to identify strains that are effective against rice sheath blight. Among these strains, strain S17-377 showed remarkable antifungal activity, resulting in a 10 mm diameter inhibitory band against R. solani. Furthermore, it exhibited a wide range of antimicrobial properties in vitro. Through genetic analysis using the 16S rDNA and recA genes, strain S17-377 was identified as Burkholderia pyrrocinia. Importantly, it was found to be non-pathogenic to onions and did not possess the virulence genes BCESM and cblA. Therefore, this strain is safe for both people and plants. The strain S17-377 showed an efficacy of 64.81% and 55.78% in controlling rice sheath blight in pot experiments and field trials, respectively. Strain S17-377 displayed persistent colonization ability in rice plants for up to 30 days after inoculation. It also induced the expression of several rice plant genes, including NH1, PR1a, PR10, PAL/ZB8, LOX, and AOS2, as well as enzymes such as POD, PPO, and PAL. Additionally, S17-377 produced proteases, chitinases, non-volatile metabolites, and biofilms. In terms of disease control, the aseptic fermentation solution of S17-377, when diluted with PDA medium at ratios of 1:20, 1:10, and 1:5, exhibited inhibition rates of 77.14%, 86.92%, and 98.26%, respectively, against R. solani. S17-377 also had noticeable effects on the expansion and collapse of fungal mycelium. Moreover, the bacterial culture filtrates(BCF) of S17-377 demonstrated high thermal stability with an inhibition rate of 96.16%, even after being subjected to a temperature of 121 °C for 30 min. The BCF of strain S17-377 exhibited significant inhibition of R. solani, with inhibition rates of 95.23%, 94.43%, and 75.11% for the n-butanol, crude protein, and crude lipopeptide extracts, respectively. Further analysis of the n-butanol extract using liquid chromatography-mass spectrometry (LC-MS) identified eight compounds with potent antibacterial activity. These findings highlight the potential of strain S17-377 as a biocontrol agent for the management of rice sheath blight.

Transferred communities of arbuscular mycorrhizal fungal persist in novel climates and soils

Symbiotic mycorrhizal fungi strongly influence plant establishment and growth particularly in harsh environments, whereby sympatric, presumably co-adapted symbionts are considered particularly beneficial. However, the response of transferred sympatric mycorrhizal fungal communities to new environments remains largely ignored. We therefore studied the relative importance of initial inoculum, soil and climatic conditions on the composition, diversity and root colonization ability of arbuscular mycorrhizal fungal (AMF) communities. To do so, we analyzed the AMF communities in an extensive experiment with two ecotypes of Bouteloua gracilis planted in their sites of origin and in four new sites differing in climate and soil properties.After three seasons of growth, the sympatric AMF communities were little changed by the new abiotic conditions. The composition of the AMF communities in plant roots was most strongly determined by the initial inoculum, while the contribution of divergent soil and climatic conditions was an order of magnitude smaller. The levels of root colonization by AMF, in contrast, were significantly influenced by climatic and soil conditions and did not differ among communities of different origins. Their pattern indicates that mycorrhiza formation is facilitated in the plant's sympatric soil and climatic conditions, but also that transferred AMF communities adjust mycorrhiza formation to new abiotic conditions.

Impact of Mechanical Removal on the Regeneration and Colonization Abilities of the Alien Aquatic Macrophyte Egeria densa.

The development of aquatic plant beds can obstruct boat traffic, hinder the practice of water activities, and impact the functioning of freshwaters. In order to mitigate their effects, mechanical removal is often the preferred management solution. The objective of this study was to test, in mesocosms, the effect of frequency (none, one, and two cuts) and cutting dates (May and/or July) on the regeneration and colonization capabilities of the aquatic plant Egeria densa, an invasive alien species in France. The cutting date had no effect on the capabilities of E. densa, but the two cuts significantly reduced the plant's biomass. Removal produced numerous fragments, which exhibited very high survival and anchoring rates. However, summer removal produced fragments with lower regeneration and colonization abilities compared to fragments from spring cutting. Mechanical removal only temporarily reduced the biomass of the aquatic plant beds and could promote the formation of new beds from the fragments generated by management and dispersed by water flow.

Microevolution of Salmonella 4,[5],12:i:- derived from Salmonella enterica serovar Typhimurium through complicated transpositions

Salmonella enterica subsp. enterica serovar 4,[5],12:i:- (Salmonella 4,[5],12:i:-), derived from S. Typhimurium, has become the dominant serotype causing human salmonellosis. In this study, we define the genetic mechanism of the generation of Salmonella 4,[5],12:i:- from S. Typhimurium through complicated transpositions and demonstrate that Salmonella 4,[5],12:i:- displays more efficient colonization and survival abilities in mice than its parent S. Typhimurium strain. We identified intermediate strains carrying both resistance regions (RRs) and the fljAB operon for the generation of Salmonella 4,[5],12:i:-. The insertion of RR3 into the chromosomal hin-iroB site of S. Typhimurium produced RR3-S. Typhimurium as a primary intermediate. Salmonella 4,[5],12:i:- was then produced by replacing the fljAB operon and/or its flanking sequences through intramolecular transpositions mediated by IS26 and/or IS1R elements in RR3-S. Typhimurium, which was further confirmed both invitro and invivo. Overall, we demonstrate the molecular mechanism underlying the origin, generation, and advantage of RRs-Salmonella 4,[5],12:i:- from S. Typhimurium.

Artificial light quality changes colonization ability of biocontrol agents under greenhouse conditions

Artificial light quality changes colonization ability of biocontrol agents under greenhouse conditions

Pectic homogalacturonan sensed by Bacillus acts as host associated cue to promote establishment and persistence in the rhizosphere

Bacillus velezensis isolates are among the most promising plant-associated beneficial bacteria used as biocontrol agents. However, various aspects of the chemical communication between the plant and these beneficials, determining root colonization ability, remain poorly described. Here we investigated the molecular basis of such interkingdom interaction occurring upon contact between Bacillus velezensis and its host via the sensing of pectin backbone homogalacturonan (HG). We showed that B. velezensis stimulates key developmental traits via a dynamic process involving two conserved pectinolytic enzymes. This response integrates transcriptional changes leading to the switch from planktonic to sessile cells, a strong increase in biofilm formation, and an accelerated sporulation dynamics while conserving the potential to efficiently produce specialized secondary metabolites. As a whole, we anticipate that this response of Bacillus to cell wall-derived host cues contributes to its establishment and persistence in the competitive rhizosphere niche and ipso facto to its activity as biocontrol agent.

Acquisition of a novel conjugative multidrug-resistant hypervirulent plasmid leads to hypervirulence in clinical carbapenem-resistant Klebsiella pneumoniae strains.

The co-occurrence of plasmid-mediated multidrug resistance and hypervirulence in epidemic carbapenem-resistant Klebsiella pneumoniae has emerged as a global public health issue. In this study, an ST23 carbapenem-resistant hypervirulent K. pneumoniae (CR-HvKP) strain VH1-2 was identified from cucumber in China and harbored a novel hybrid plasmid pVH1-2-VIR. The plasmid pVH1-2-VIR carrying both virulence and multidrug-resistance (MDR) genes was likely generated through the recombination of a virulence plasmid and an IncFIIK conjugative MDR plasmid in clinical ST23 18622 isolated from a sputum sample. The plasmid pVH1-2-VIR exhibited the capacity for transfer to the clinical ST11 carbapenem-resistant K. pneumoniae (CRKP) strain via conjugation assay. Acquisition of pVH1-2-VIR plasmid directly converted a CRKP into CR-HvKP strain characterized by hypermucoviscosity, heightened virulence for Galleria mellonella larvae, and increased colonization ability in the mouse intestine. The emergence of such a hybrid plasmid may expedite the spread of CR-HvKP strains, posing a significant risk to human health.

Different microbial assemblage colonized on microplastics and clay particles in aerobic sludge treatment

In this study, a combination of property analysis and high–throughput sequencing was used to investigate the microbial colonization ability and their community structures and functions in polypropylene microplastics (PPMPs), polystyrene microplastics (PSMPs) and montmorillonite (MMT), respectively as the representatives of artificial and natural substrates in aerobic sludge treatment. After 45 d of incubation, the surface properties of substrates were altered with the increased oxygen functional groups and surface roughness, indicating microbial settlement. Moreover, MPs had different microbial structures from that of MMT, and PSMPs exhibited higher microbial diversity and abundance than PPMPs and MMT. Also, these substrates changed the inherent ecological niche in sludge. Especially, the abundance of some pathogens (e.g., Pseudomonas, Klebsiella and Flavobacterium) was increased in MPs, and the disease risk of Kyoto Encyclopedia of Genes and Genomes metabolic pathway (e.g., Infectious diseases: Bacterial, Infectious diseases: Parasitic and Immune diseases) was higher. Also, the presence of MPs inhibited the decomposition of organic matter including soluble chemical oxygen demand and protein compared to natural substrates. The findings revealed the crucial vector role of MPs for microbes and the effect on aerobic sludge treatment, highlighting the necessity of MP removal in sludge.

The Response Regulator VC1795 of Vibrio Pathogenicity Island-2 Contributes to Intestinal Colonization by Vibrio cholerae.

Vibrio cholerae is an intestinal pathogen that can cause severe diarrheal disease. The disease has afflicted millions of people since the 19th century and has aroused global concern. The Vibrio Pathogenicity Island-2 (VPI-2) is a 57.3 kb region, VC1758-VC1809, which is present in choleragenic V. cholerae. At present, little is known about the function of VC1795 in the VPI-2 of V. cholerae. In this study, the intestinal colonization ability of the ΔVC1795 strain was significantly reduced compared to that of the wild-type strain, and the colonization ability was restored to the wild-type strain after VC1795 gene replacement. This result indicated that the VC1795 gene plays a key role in the intestinal colonization and pathogenicity of V. cholerae. Then, we explored the upstream and downstream regulation mechanisms of the VC1795 gene. Cyclic adenylate receptor protein (CRP) was identified as being located upstream of VC1795 by a DNA pull-down assay and electrophoretic mobility shift assays (EMSAs) and negatively regulating the expression of VC1795. In addition, the results of Chromatin immunoprecipitation followed by sequencing (ChIP-seq), EMSAs, and Quantitative Real-Time Polymerase Chain Reaction (qRT-PCR) indicated that VC1795 directly negatively regulates the expression of its downstream gene, VC1794. Furthermore, by using qRT-PCR, we hypothesized that VC1795 indirectly positively regulates the toxin-coregulated pilus (TCP) cluster to influence the colonization ability of V. cholerae in intestinal tracts. In short, our findings support the key regulatory role of VC1795 in bacterial pathogenesis as well as lay the groundwork for the further determination of the complex regulatory network of VC1795 in bacteria.

Characterization and anti-inflammatory effect of selenium-enriched probiotic Bacillus amyloliquefaciens C-1, a potential postbiotics

A patented strain of Bacillus amyloliquefaciens C-1 in our laboratory could produce functional sodium selenite (Na2SeO3) under optimized fermentation conditions. With the strong stress resistance and abundant secondary metabolites, C-1 showed potential to be developed as selenium-enriched postbiotics. C-1 has the ability to synthesize SeNPs when incubated with 100 μg/ml Na2SeO3 for 30 h at 30 °C aerobically with 10% seeds-culture. The transformation rate from Na2SeO3 into SeNPs reached to 55.51%. After selenium enrichment, there were no significant morphology changes in C-1 cells but obvious SeNPs accumulated inside of cells, observed by scanning electron microscope and transmission electron microscope, verified by energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. SeNPs had antioxidant activity in radical scavenge of superoxide (O2−), Hydroxyl radical (OH−) and 1,1-diphenyl-2-picryl-hydrazine (DPPH), where scavenging ability of OH− is the highest. Selenium-enriched C-1 had obvious anti-inflammatory effect in protecting integrity of Caco-2 cell membrane destroyed by S. typhimurium; it could preventing inflammatory damage in Caco-2 stressed by 200 μM H2O2 for 4 h, with significantly reduced expression of IL-8 (1.687 vs. 3.487, P = 0.01), IL-1β (1.031 vs. 5.000, P < 0.001), TNF-α (2.677 vs. 9.331, P < 0.001), increased Claudin-1 (0.971 vs. 0.611, P < 0.001) and Occludin (0.750 vs. 0.307, P < 0.001). Transcriptome data analysis showed that there were 381 differential genes in the vegetative growth stage and 1674 differential genes in the sporulation stage of C-1 with and without selenium-enrichment. A total of 22 ABC transporter protein-related genes at vegetative stage and 70 ABC transporter protein-related genes at sporulation stage were founded. Genes encoding MsrA, thiol, glutathione and thioredoxin reduction were significantly up-regulated; genes related to ATP synthase such as atpA and atpD genes showed down-regulated during vegetative stage; the flagellar-related genes (flgG, fliM, fliL, and fliJ) showed down-regulated during sporulation stage. The motility, chemotaxis and colonization ability were weakened along with synthesized SeNPs accumulated intracellular at sporulation stage. B. amyloliquefaciens C-1 could convert extracellular selenite into intracellular SeNPs through the oxidation–reduction pathway, with strong selenium-enriched metabolism. The SeNPs and selenium-enriched cells had potential to be developed as nano-selenium biomaterials and selenium-enriched postbiotics.

Silymarin-Loaded Tin(IV) Nanoparticles Exhibit Enhanced Bioavailability and Antiproliferative Effects on Colorectal Cancer Cells.

Silymarin (SM) exhibits potential therapeutic effects due to having antioxidant activity. However, the low solubility and bioavailability of SM restrict its biological performance. To overcome this limitation, this study aimed to develop a nanoformulation composed of SM and dimethyltindichloride and investigate the effect of SM-loaded Sn nanoparticles on cancer cell growth and survival. An SM-Sn complex was synthesized and then characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FTIR), EDS-MAP, dynamic light scattering (DLS), and ζ-potential analysis. After that, the SW480 colorectal cancer cell line was treated with different concentrations of SM and the SM-Sn complex. Cell viability was examined through the 3-(4,5-dimethylthiazole-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, analyzing apoptosis, and live-dead assay. The lipid peroxidation rate was assessed through the measurement of thiobarbituric acid (TBA). Intracellular reactive oxygen species (ROS) level and cell population in the cell cycle were measured using a flow cytometry instrument. To evaluate the colonization ability of SW480 cells, a colony formation assay was performed. Gene expression analysis was also conducted using a real-time polymerase chain reaction (PCR) technique. The findings of this study revealed the effectiveness of the SM-Sn complex in decreasing SW480 cell viability by inducing cell death-associated mechanisms. We found that the SM-Sn complex increases intracellular ROS level and malondialdehyde (MDA) content. It was also revealed that the SM-Sn complex induces cell cycle arrest and the expression of apoptotic genes. In addition, the SM-Sn complex could effectively hinder SW480 cells from constituting colonies. We conclude that the use of tin(IV) as a scaffold for enhanced delivery of SM could be considered an efficient option for inhibiting cancer cell proliferation and survival.

Regulation of mycorrhizal colonization under stress in tomato depends on symbiotic efficiency

The mutualistic symbiosis between plants and arbuscular mycorrhizal (AM) fungi is based on a balanced nutrient exchange between both partners, with the plant achieving improved nutrition and stress tolerance. The symbiosis is finely-tuned according to plant’s needs and surrounding conditions, usually through phytohormonal signaling. Thus, environmental conditions or stress factors modulating phytohormone signaling may influence the symbiosis. This study compares the colonization abilities of 2 AM fungal species, Funneliformis mosseae and Rhizophagus irregularis, independently or in combination, in tomato plants subjected to different stress conditions. These included salt stress and systemic defense activation by aboveground application of the defense-related hormones methyl jasmonate, abscisic acid and salicylic acid. The results show that root colonization by the two fungal species differs depending on the stress treatment. Nutrient and transcriptional analyses revealed that changes in colonization correlated with differential regulation of nutrient exchange, plant defensive responses, and symbiosis regulatory genes. Specifically, under salt stress R. irregularis colonization decreased, while F. mosseae colonization was promoted. These differential regulation of colonization under stress positively correlated with changes in the functionality of the symbiosis. Overall, the results support that the benefits provided by each AM fungi influence carbon reward and determines the control of root colonization by the host plant.

Bacteriocin-Producing Escherichia coli Q5 and C41 with Potential Probiotic Properties: In Silico, In Vitro, and In Vivo Studies.

Commensal bacteriocin-producing Escherichia coli are of interest for possible use as probiotics to selectively control the spread of pathogenic bacteria. Here, we evaluated the biosafety and efficacy of two new bacteriocin-producing E. coli strains, Q5 (VKM B-3706D) and C41 (VKM B-3707D), isolated from healthy farm animals. The genomes of both strains were sequenced, and genes responsible for the antagonistic and colonization abilities of each strain were identified. In vitro studies have shown that both strains were medium-adhesive and demonstrated antagonistic activity against most enteropathogens tested. Oral administration of 5 × 108 to 5 × 1010 colony-forming units of both strains to rats with drinking water did not cause any disease symptoms or side effects. Short-term (5 days) oral administration of both strains protected rats from colonization and pathogenic effects of a toxigenic beta-lactam-resistant strain of E. coli C55 and helped preserve intestinal homeostasis. Taken together, these in silico, in vitro, and in vivo data indicate that both strains (and especially E. coli Q5) can be potentially used for the prevention of colibacillosis in farm animals.

Effect of the zinc transporter ZupT on the virulence mechanisms of mesophilic Aeromonas salmonicida SRW‐OG1

AbstractAs a typical psychrophilic bacterial pathogen, Aeromonas salmonicida causes furunculosis in wild and farmed freshwater and marine fish, leading to substantial economic losses in the global aquaculture industry. Previous studies have shown that A. salmonicida is unable to grow above 25°C, hence limiting its infection to cold‐water fish. However, we isolated A. salmonicida SRW‐OG1, a mesophilic pathogenic strain from the warm‐water fish Epinephelus coioides. Through RNA‐seq analysis, we observe significant upregulation of the zupT gene at 28°C. ZupT is a member of zinc‐regulated transporters and iron‐regulated transporter‐like proteins (ZIP family) and is closely associated with transcriptional regulation of virulence in certain pathogens. Consequently, our study aimed to examine the role of zupT during A. salmonicida SRW‐OG1 infection at high temperatures. Our findings demonstrate that the zupT‐RNAi strain exhibits severe growth restriction under limited Zn2+ and Fe2+ conditions. Notably, this strain shows significantly reduced mortality rates and colonization abilities. Moreover, its motility, biofilm formation, adhesion, and hemolytic activities are significantly diminished. Confocal laser scanning microscopy reveals earlier and accelerated biofilm dissociation in the zupT‐RNAi strain. Analysis of extracellular products at 36 h indicates a considerable reduction in relative extracellular protein content in the zupT‐RNAi strain. Taken together, our results highlight the vital role of the zupT gene in zinc transport and the fitness of A. salmonicida SRW‐OG1 within the host.

Test of the colonization ability of the invasive alien plant Flaveria bidentis (Asteraceae) in southern China

Test of the colonization ability of the invasive alien plant Flaveria bidentis (Asteraceae) in southern China

Spatial targeting of woodland creation can reduce the colonisation credit of woodland plants

Abstract Colonisation credit refers to the temporal lag between positive conservation actions and species' responses and may be one of the reasons we fail to meet short‐term conservation targets. This is particularly evident in woodlands which take decades to develop and harbour slow colonising species. Given global objectives to increase woodland cover, it is important to know the timeframe within which colonisation credit will be fulfilled. The colonisation of woodland plants was examined in recent woodlands, created between 15 and 80 years ago, and located adjacent or isolated from existing ancient woodlands. Colonisation credit was calculated as the proportion of understory woodland plant species in the nearest ancient woodland which had not colonised recent woodlands. Looking at individual species traits also allowed us to tease apart their impact on the species colonisation and establishment ability. Spatial adjacency between created and ancient woodland reduced colonisation credit by an average of 28%, and more mature created woodlands (50–80 years old) had fulfilled 24% more of their colonisation credit on average than younger created woodlands (15–21 years old). However, mature woodlands created adjacent to ancient woodlands had still only been colonised by an average of 72% of the available species pool. Plants which had reached adjacent created woodlands were dispersed by a range of mechanisms, where those that had reached more isolated sites were largely dispersed by birds or mammals. Low community weighted mean shade tolerance, high community weighted nutrient affiliation, and the dominance of Hedera helix suggest that competition from dominant natives may be preventing certain species establishing in new woodlands. This research demonstrates the need to account for appropriate time‐lags when setting biodiversity targets, with most sites still displaying colonisation credit decades after they were created. The results also indicate that spatially targeting woodland creation adjacent to species‐rich mature woodlands should be prioritised. Still, poor local habitat conditions may lead to the dominance of specific competitors which prevent a range of other species from establishing. Local management interventions such as translocations and tree thinning may ameliorate this but further research is needed.

Effect of varying concentrations of Tryptamine on the development of Zea Mays

Rhizobium is a widely acknowledged bacterium due to its symbiotic relationship, particularly with leguminous forages. It forms nodules, a specialized structure, in approximately 90% of the Fabaceae family and exhibits various methods to enhance soil fertility. Rhizobium can form a symbiotic relationship with non-leguminous plants due to its exceptional colonization abilities, which can contribute to enhanced crop growth. Physiological precursors are utilized in conjunction with rhizobium due to their superior water solubility, consistent hormone supply, and cost-effectiveness. The aim of this investigation was to assess the impact of precursor, both with and without Tryptamine, on the growth parameters of maize. A total of six treatments consisting of tryptamine dilutions were planned for the experiment. The findings indicate that Tryptamine @ 10-4 (T5) resulted in the greatest shoot length (43.6 cm), fresh weight (11.78 g) and dry weight (1.67 g), root length (36 cm), fresh weight (4.91 g) and dry weight (1.99 g), as well as chlorophyll (a) and (b) levels (1.05 and 0.77 mg g-1). The efficacy of precursor application has been determined and warrants further examination in diverse ecologies.

Biocontrol of Corynespora cassiicola in soybean using a new phenethyl alcohol-producing Meyerozyma caribbica strain

Corynespora cassiicola is a hazardous fungal pathogen that causes target spot disease in soybean. Numerous resistant C. cassiicola strains have emerged during recent years, leading to uncontrolled spreads and enormous economic losses in several soybean production areas. For these reasons, new methods for the control of this pathogen are urgently needed. In this study, a new Meyerozyma caribbica strain, NJC41, was isolated from C. cassiicola-infected soybean plants in China and identified by ITS and LSU sequencing. NJC41 inhibited C. cassiicola mycelial growth, and showed high colonization ability in soybean pods, maintaining its population for one week. NJC41 produced antifungal phenethyl alcohol, which was detected at 44.6 μg/mL in NJC41 secretions, and competed for space and nutrients with C. cassiicola. Curative application of 1 × 109 cells/mL NJC41 reduced C. cassiicola symptoms by 47.1%, providing higher curative efficacy than commercial fungicide carbendazim (29.8% lesion length inhibition). This study reveals the first biocontrol method for the management of target spot disease in soybean.

Functional Characterization of FeoAB in Iron Acquisition and Pathogenicity in Riemerella anatipestifer.

The bacterium Riemerella anatipestifer requires iron for growth, but the mechanism of iron uptake is not fully understood. In this study, we disrupted the Feo system and characterized its function in iron import in R. anatipestifer ATCC 11845. Compared to the parent strain, the growth of the ΔfeoA, ΔfeoB, and ΔfeoAB strains was affected under Fe3+-limited conditions, since the absence of the feo system led to less intracellular iron than in the parent strain. In parallel, the ΔfeoAB strain was shown to be less sensitive to streptonigrin, an antibiotic that requires free iron to function. The sensitivity of the ΔfeoAB strain to hydrogen peroxide was also observed to be diminished compared with that of the parent strain, which could be related to the reduced intracellular iron content in the ΔfeoAB strain. Further research revealed that feoA and feoB were directly regulated by iron through the Fur regulator and that the transcript levels of feoA and feoB were significantly increased in medium supplemented with 1 mM MnCl2, 400 μM ZnSO4, and 200 μM CuCl2. Finally, it was shown that the ΔfeoAB strain of R. anatipestifer ATCC 11845 was significantly impaired in its ability to colonize the blood, liver, and brain of ducklings. Taken together, these results demonstrated that FeoAB supports ferrous iron acquisition in R. anatipestifer and plays an important role in R. anatipestifer colonization. IMPORTANCE In Gram-negative bacteria, the Feo system is an important ferrous iron transport system. R. anatipestifer encodes an Feo system, but its function unknown. As iron uptake may be required for oxidative stress protection and virulence, understanding the contribution of iron transporters to these processes is crucial. This study showed that the ΔfeoAB strain is debilitated in its ability to import iron and that its intracellular iron content was constitutively low, which enhanced the resistance of the deficient strain to H2O2. We were surprised to find that, in addition to responding to iron, the Feo system may play an important role in sensing manganese, zinc, and copper stress. The reduced colonization ability of the ΔfeoAB strain also sheds light on the role of iron transporters in host-pathogen interactions. This study is important for understanding the cross talk between iron and other metal transport pathways, as well as the pathogenic mechanism in R. anatipestifer.

Vibrio splendidus Fur regulates virulence gene expression, swarming motility, and biofilm formation, affecting its pathogenicity in Apostichopus japonicus.

Vibrio splendidus is an opportunistic pathogen that causes skin ulcer syndrome and results in huge losses to the Apostichopus japonicus breeding industry. Ferric uptake regulator (Fur) is a global transcription factor that affects varieties of virulence-related functions in pathogenic bacteria. However, the role of the V. splendidus fur (Vsfur) gene in the pathogenesis of V. splendidus remains unclear. Hence, we constructed a Vsfur knock-down mutant of the V. splendidus strain (MTVs) to investigate the role of the gene in the effect of biofilm, swarming motility, and virulence on A. japonicus. The result showed that the growth curves of the wild-type V. splendidus strain (WTVs) and MTVs were almost consistent. Compared with WTVs, the significant increases in the transcription of the virulence-related gene Vshppd mRNA were 3.54- and 7.33-fold in MTVs at the OD600 of 1.0 and 1.5, respectively. Similarly, compared with WTVs, the significant increases in the transcription of Vsm mRNA were 2.10- and 15.92-fold in MTVs at the OD600 of 1.0 and 1.5, respectively. On the contrary, the mRNA level of the flagellum assembly gene Vsflic was downregulated 0.56-fold in MTVs at the OD600 of 1.0 compared with the WTVs. MTVs caused delayed disease onset time and reduced A. japonicus mortality. The median lethal doses of WTVs and MTVs were 9.116 × 106 and 1.658 × 1011 CFU·ml-1, respectively. Compared with WTVs, the colonization abilities of MTVs to the muscle, intestine, tentacle, and coelomic fluid of A. japonicus were significantly reduced. Correspondingly, the swarming motility and biofilm formation in normal and iron-replete conditions were remarkably decreased compared with those of WTVs. Overall, these results demonstrate that Vsfur contributes to the pathogenesis of V. splendidus by regulating virulence-related gene expression and affecting its swarming and biofilm formation abilities.