Extracellular Polysaccharide Production Research Articles

Analyses of the Effects of Arginine, Nicotine, Serotype and Collagen-Binding Proteins on Biofilm Development by 33 Strains of Streptococcus mutans.

Streptococcus mutans serotype k strains comprise <3% of oral isolates of S. mutans but are prominent in diseased cardiovascular (CV) tissue. Collagen binding protein (CBP) genes, cbm and cnm, are prevalent in serotype k strains and are associated with endothelial cell invasion. Nicotine increases biofilm formation by serotype c strains of S. mutans, but its effects on serotype k strains and strains with CBP are unknown. Saliva contains arginine which alters certain properties of the extracellular polysaccharides (EPS) in S. mutans biofilm. We examined whether nicotine and arginine affect sucrose-induced biofilm of S. mutans serotypes k (n = 23) and c (n = 10) strains with and without CBP genes. Biofilm mass, metabolism, bacterial proliferation, and EPS production were assessed. Nicotine increased biomass and metabolic activity (p < 0.0001); arginine alone had no effect. The presence of a CBP gene (either cbm or cnm) had a significant effect on biofilm production, but serotype did not. Nicotine increased bacterial proliferation and the effect was greater in CBP + strains compared to strains lacking CBP genes. Addition of arginine with nicotine decreased both bacterial mass and EPS compared to biofilm grown in nicotine alone. EPS production was greater in cnm + than cbm + strains (p < 0.0001). Given the findings of S. mutans in diseased CV tissue, a nicotine induced increase in biofilm production by CBP + strains may be a key link between tobacco use and CV diseases.

CO2 improves the microalgal-bacterial granular sludge towards carbon-negative wastewater treatment

As a promising wastewater treatment technology, little is known about whether the greenhouse gas CO2 can be applied for microalgal-bacterial granular sludge (MBGS) process. This article applied CO2 for improving MBGS process. It was found that the physical structure of MBGS with no CO2 addition appeared to have a trend to be loose and disintegrated, with a sludge volume index at 5 min (SVI5) of over 150 mL/g and an average pore size of 35 nm in 60 d operation. However, CO2 could maintain the compact and integrated structure of MBGS with a SVI5 lower than 50 mL/g and an average pore size ranging from 10 to 13 nm. CO2 could enhance the production of extracellular polysaccharides and aromatic protein, thus favoring the granular stability of MBGS. CO2 could change the aqueous environment, e.g. lowering the pH values, which resulted in different microbial communities as well as metabolic potentials of MBGS. As for the reactor performance, CO2 could significantly improve the removals of organics and phosphorus, evidenced by the enhancement of genes encoding acetate-CoA ligase and ATPase, respectively. Although the mass ratio of algae to bacteria was elevated by CO2 addition, the ammonia removal related enzymes of glutamate dehydrogenase and glutamine synthetase could be negatively and positively impacted by CO2, respectively. Mass balance analysis of carbon indicated that CO2 could provide additional carbon source as well as enhance the buffering capacity for the MBGS system. Further estimations suggested that the MBGS process could achieve a carbon-negative objective for municipal wastewater treatment by supplying CO2 as additional carbon source. Hence, CO2 supply for MBGS process in municipal wastewater treatment can be deemed as a two-birds-one-stone strategy, i.e. maintaining the granular stability and eliminating the carbon emission. This article can advance our basic knowledge on MBGS process towards environment-sustainable wastewater treatment.

Paenibacillus polymyxa A26 and Its Surfactant-Deficient Mutant Degradation of Polycyclic Aromatic Hydrocarbons

We compared the ability of two bacterial strains, Paenibacillus polymyxa A26 and P. polymyxa A26Sfp, for biodegradation of naphthalene (NAP). The studies were performed under simulated laboratory conditions, in liquid medium and soil with different carbon sources, pH and salt contents. Changes in the luminescence inhibition of Aliivibrio fischeri, as an indicator of the baseline toxicity, were observed in degradation mixtures during 7 days of incubation. While both strains expressed the best growth and NAP degradation ability in the minimal salt medium containing sucrose and 5% NaCl at pH 7 and 8, the mutant strain remained effective even under extreme conditions. A26Sfp was found to be an efficient and potentially industrially important polycyclic aromatic hydrocarbon degradation strain. Its extracellular polysaccharide production is 30%, and glucan production is twice that of the wild type A 26. The surface tension reduction ability was ascertained as 25–30% increased emulsification ability.

Optimization of Fermentation Medium Formula and Fermentation Conditions of Tremella fuciformis Spore Polysaccharide and Its Scale-up Fermentation Experiment

In order to develop a submerged fermentation medium for high-yield extracellular polysaccharides (EPS) of Tremella fuciformis spore, to improve its fermentation yield and achieve large-scale production applications, this study used a single factor method to explore the effects of different sources of carbon and nitrogen sources and nutrient elements on the yield of Tremella polysaccharides. Through the Plackett-Burman and Box-Behnken response surface design to obtain the high-yield EPS fermentation medium and fermentation conditions, and verified the optimization results in a 50 L fermentation tank. The results showed that the fermentation medium of Tremella spores with high production of extracellular polysaccharides was: Glucose 35 g/L, NaCl 0.6 g/L, compound nitrogen source (yeast extracts:corn steep dry powder=1:1) 3.6 g/L, MgSO4 0.5 g/L, KH2PO4 1 g/L; Optimal fermentation conditions were: 27 ℃, pH5, fermentation for 6 days, inoculation amount 3%(v/v) and shaker speed 150 r/min. After optimization, the yield of extracellular polysaccharide from Tremella spore was 214.45 mg/100 mL, with 8.56 times of that before optimization. In the 50 L fermentation tank, the polysaccharide yield was 258.78 mg/100 mL with 21.03% higher than the shake flask experiment. This optimization of the fermentation process significantly promoted the production of extracellular polysaccharides from Tremella spore, which would provide a theoretical support for its large-scale industrial production.

Anti-Biofilm Activity of Cannabigerol against Streptococcus mutans.

Streptococcus mutans is a common cariogenic bacterium in the oral cavity involved in plaque formation. Previous studies showed that Cannabigerol (CBG) has bacteriostatic and bacteriocidic activity against S. mutans. The aim of the present study was to study its effect on S. mutans biofilm formation and dispersion. S. mutans was cultivated in the presence of CBG, and the resulting biofilms were examined by CV staining, MTT assay, qPCR, biofilm tracer, optical profilometry, and SEM. Gene expression was determined by real-time qPCR, extracellular polysaccharide (EPS) production was determined by Congo Red, and reactive oxygen species (ROS) were determined using DCFH-DA. CBG prevented the biofilm formation of S. mutans shown by reduced biofilm biomass, decreased biofilm thickness, less EPS production, reduced DNA content, diminished metabolic activity, and increased ROS levels. CBG altered the biofilm roughness profile, resulting in a smoother biofilm surface. When treating preformed biofilms, CBG reduced the metabolic activity of S. mutans with a transient effect on the biomass. CBG reduced the expression of various genes involved in essential metabolic pathways related to the cariogenic properties of S. mutans biofilms. Our data show that CBG has anti-biofilm activities against S. mutans and might be a potential drug for preventive treatment of dental caries.

Effective immobilization of heavy metals via reactive barrier by rhizosphere bacteria and their biofilms

As the portal of plants, rhizosphere microorganisms play an essential role in controlling the species, transformation, and bioavailability of heavy metals, yet the potential passivation mechanism is still unclear. In this study, two heavy metal resistant and growth-promoting rhizosphere bacteria were screened, and their mechanisms in dealing with external stress and immobilizing heavy metal were explored. The results showed that heavy metals inhibited the ability of Pseudomonas sp. H13 and Brevundomonas sp. H16 to promote plant growth, but stimulated the production of extracellular polysaccharides and inorganic labile sulfide, and enhanced biofilm formation, thereby significantly improved the removal efficiency of Cu2+, Zn2+, Cd2+, and Pb2+. Compared with H16, the biofilm of H13 disintegrated rapidly in the later stage, so more metal ions were adsorbed on the planktonic cells. The C–OH and PO groups related to polysaccharides play a crucial role in heavy metal adsorption, and the immobilization mechanism of the planktonic cell is mainly ion exchange and group complex, but for H16, intracellular enrichment cannot be ignored. Functional group complexes played a dominant role in biofilm, and the immobilized heavy metals were more difficult to release into the environment. This study highlighted the potential application prospects of biofilm bacteria in heavy metal remediation and explained the reactive barrier of rhizosphere bacteria to heavy metals.

The effects of quorum sensing molecule farnesol on the yield and activity of extracellular polysaccharide from Grifola frondosa in liquid fermentation

A strategy by exogenous addition of quorum sensing molecule farnesol to improve the production, antioxidant activity and antitumor activity of extracellular polysaccharide (EPS) of Grifola frondosa by liquid fermentation was proposed in the study. The highest yield of EPS induced by farnesol was 1.25 g/L, which was 150% higher than that of the control. Four polysaccharides including EPS-C-0M, EPS-C-0.2M, EPS-F-0M and EPS-F-0.2M were extracted and purified under the conditions of control and farnesol respectively. The physicochemical properties, antioxidant activities and antitumor activities were studied. Their chemical composition differed in sugar, protein and uronic acid contents, and they were composed of six constituent monosaccharides with different ratios, with the average molecular weights of 1.12 × 103, 1.89 × 103, 1.41 × 103 and 2.02 × 103 kDa, respectively. They presented similar FT-IR spectra, but different surface morphology. Antioxidant experiments showed that they had strong scavenging activities on ABTS+, hydroxyl radical, O2− and DPPH radical. Antitumor experiments showed that they had strong inhibitory effects on human cervical cancer (HeLa) cells and human liver cancer cells (HepG2) cells. Among the four polysaccharides, EPS-F-0.2M showed the highest antioxidant and antitumor activities, indicating that farnesol could regulate the biological activity of EPS by affecting structure and properties. These results demonstrated that appropriate adjustment of culture conditions had potential application in the development of polysaccharides with high antioxidant and antitumor activity. It provided a new strategy to enhance the production and bioactivity of edible and medicinal fungal polysaccharides by using quorum sensing molecules.

Identification and characteristics of Pantoea cypripedii 4A strain producing high molecular exopolysaccharide

Searching for new microorganisms with great potential for the synthesis of high-molecular exopolysaccharides possessing some useful traits is very important in the scope of certain industries. The bacterial strain Pantoea cypripedii 4A isolated by direct plating on a rich agar medium was studied in this work as a potential producer of extracellular polysaccharides. This strain was isolated from forest litter mixed with the topsoil of the M.A. Zablotsky Prioksko-Terrasny Reserve. The Pantoea cypripedii 4A strain is capable of synthesizing EPS that was confirmed by the Podobedov-Molish reaction (a qualitative reaction to carbohydrates in the medium) on a medium supplemented with 5% sucrose. Gel permeation chromatography confirmed that the isolated strain produces an exopolysaccharide with a molecular weight of about 1.69 MDa on a medium supplemented with 5% sucrose. However, the presence of two lower molecular weight peaks may indicate that the resulting product has heterogeneous structure. The yield of dry biopolymer when growing the strain on a mineral medium with sucrose at a final concentration of 5% without adding additional components, such as microelements, was 8.5 g/l. One of the important characteristics of EPS is the viscosity of their aqueous solutions. The measured dynamic viscosity of a 10% EPS solution synthesized by Pantoea cypripedii 4A was 1.728 mPa s. Despite the fact that the production of extracellular polysaccharides is often enhanced under stress conditions, neither reduced oxygen concentration, nor low temperature conditions did affect the EPS biosynthesis by the studied strain.

Screening and Characterization of Two Extracellular Polysaccharide-Producing Bacteria from the Biocrust of the Mu Us Desert.

The extracellular polysaccharide (EPS) matrix embedding microbial cells and soil particles plays an important role in the development of biological soil crusts (BSCs), which is widely recognized as beneficial to soil fertility in dryland worldwide. This study examined the EPS-producing bacterial strains YL24-1 and YL24-3 isolated from sandy soil in the Mu Us Desert in Yulin, Shaanxi province, China. The strains YL24-1 and YL24-3 were able to efficiently produce EPS; the levels of EPS were determined to be 257.22 μg/mL and 83.41 μg/mL in cultures grown for 72 h and were identified as Sinorhizobium meliloti and Pedobacter sp., respectively. When the strain YL24-3 was compared to Pedobacter yulinensis YL28-9T using 16S rRNA gene sequencing, the resemblance was 98.6% and the strain was classified as Pedobacter sp. using physiological and biochemical analysis. Furthermore, strain YL24-3 was also identified as a subspecies of Pedobacter yulinensis YL28-9T on the basis of DNA–DNA hybridization and polar lipid analysis compared with YL28-9T. On the basis of the EPS-related genes of relevant strains in the GenBank, several EPS-related genes were cloned and sequenced in the strain YL24-1, including those potentially involved in EPS synthesis, assembly, transport, and secretion. Given the differences of the strains in EPS production, it is possible that the differences in gene sequences result in variations in the enzyme/protein activities for EPS biosynthesis, assembly, transport, and secretion. The results provide preliminary evidence of various contributions of bacterial strains to the formation of EPS matrix in the Mu Us Desert.

The Opportunity of Spent Bleaching Earth (Bentonite) and Silica Solubilizing Bacteria as Silica Source for Induction of Secondary Metabolites Production in Plants

Background: CPO refining which produces solid waste namely spent bleaching earth (SBE) in large quantities can pollute the environment. SBE from bentonite ores contains large amounts of silica, so it can be an alternative source of silica minerals. Silica plays an important role in increasing plant resistance and bioactive plant compound products. Methods: The application of Si in plants can increase secondary metabolites such as phenolic and anti-fungal compounds in response to disease pathogens. However, the low solubility of silica makes silica not sufficiently available for plants. Using microorganisms as silica solubilizing bacteria helps increasing solubility of silica in the soil. Bacteria dissolve silica by removing organic acids and producing indole acetic acid (AAI), which stimulates root hairs. Results: This review presents the results of a study on the utilization of silica-rich SBE waste as a source of available silica for plants with solubilizing method using bacteria to increase plant growth and resistance, as well as increase plant secondary metabolite compounds. Conclusions: The application of silica solubilizing bacteria has been known to play an important role in providing silica for plants, through enzymatic mechanisms, namely the production of organic acids and extracellular polysaccharides.

A HU-like protein is required for full virulence in Xanthomonas campestris pv. campestris.

Bacteria harbour several abundant small DNA‐binding proteins known as nucleoid‐associated proteins (NAPs) that contribute to the structure of the bacterial nucleoid as well as to gene regulation. Although the function of NAPs as global transcriptional regulators has been comprehensively studied in the model organism Escherichia coli, their regulatory functions in other bacteria remain relatively poorly understood. Xanthomonas campestris pv. campestris (Xcc) is a gram‐negative bacterium that causes black rot disease in almost all members of the crucifer family. In previous work, we demonstrated that a Fis homologue protein, which we named Fis‐like protein (Flp), contributes to the regulation of virulence, type III secretion, and a series of other phenotypes in Xcc. Here we have examined the role of XC_1355, which is predicted to encode a DNA‐binding protein belonging to the HU family herein named HU‐like protein (Hlp). We show that mutation of XC_1355 in Xcc reduces the virulence, extracellular polysaccharide production, and cell motility, but has no effect on the production of extracellular enzymes and induction of the hypersensitive response. These data together with transcriptome analysis indicate that hlp is a previously uncharacterized gene involved in virulence that has partially overlapping and complementary functions with flp in Xcc, although the two regulators have opposite effects on the expression of genes involved in type III secretion. The findings add to our understanding of the complex regulatory pathways that act to regulate virulence in Xcc.

Impact of growth medium salinity on galactoxylan exopolysaccharides of Porphyridium purpureum

Porphyridium purpureum is a red saline microalga rich in protein and floridean starch with the ability to excrete high amounts of sulfated polysaccharides (sEPS) into the growth medium. This microalga has been used for feeding fish in aquaculture. P. purpureum is easily cultivated and could change its growth rate and composition in response to environmental variations. Thus, the effect of growth medium salinity (18, 32, and 50 g/L NaCl) on P. purpureum cell growth, biomass composition, and extracellular polysaccharides production yield and chemical structure were evaluated. A maximum growth of an estimated 5.7 × 106 cells/mL achieved at a salinity of 32 g/L NaCl, after 19 days of growth. Different from the almost unchanged biomass composition of algal cells, the yield and structure of sEPS were affected by the salinity of the growth media. The salinity of the growth media led to a slight change of the sulfation pattern of the glucuronoglucogalactoxylan, as the sEPS produced by P. purpureum growing at lower salinity tended to be more sulfated in the O-3 position of xylose and the O-6 position of glucose, whereas the sEPS at higher salinity tended to be more sulfated in the O-4 position of xylose and glucose. The sEPS produced at higher salinity also revealed higher linear 2-Gal, 3-Gal, and 4-Gal residues. In all samples, the most representative sugars residues were constituted by t-Xyl, t-Xyl-4S, 3-Xyl, 4-Xyl, t-Glc, 3-Glc-6S, t-Gal, and 2,3,4-Gal.The sEPS showed immunostimulatory effect on B lymphocytes in vitro and could be produced at large scale at an outdoor 800 L-flat panel photobioreactor with higher yield. These results pave the way for the potential use of P. purpureum sEPS to enhance humoral immune activity of fish in aquaculture.

Plant secondary metabolite, daphnetin reduces extracellular polysaccharides production and virulence factors of Ralstonia solanacearum

Plants deploy a variety of secondary metabolites to fend off pathogen attack. Certain plants could accumulate coumarins in response to infection of bacteria, fungi, virus and oomycetes. Although coumarins are generally considered toxic to microbes, the exact mechanisms are often unknown. Here, we showed that a plant secondary metabolite daphnetin functions primarily by inhibiting Ralstonia solanacearum extracellular polysaccharides (EPS) production and biofilm formation in vitro, through suppressing genes expression of xpsR, epsE, epsB and lexM. Indeed, daphnetin significantly impaired virulence of R. solanacearum on tobacco plants. Transcriptional analysis suggested that daphnetin suppresses EPS synthesis cluster genes expression through transcriptional regulator XpsR. And daphnetin alter mainly virulence factors genes involved in type III secretion system, and type IV secretion system. R. solanacearum lacking EPS synthesis genes (epsB and epsC) that do not produce EPS, showed less virulence on tobacco plants. Molecular docking results indicated that the critical residues of domain in the binding pocket of the EpsB protein interact with daphnetin via conventional hydrogen bonding and hydrophobic interactions. Collectively, we found that daphnetin has potential as a novel virulence inhibitor of R. solanacearum, directly regulates EPS synthesis genes expression.

Antibacterial Activity of Boswellia sacra Flueck. Oleoresin Extract against Porphyromonas gingivalis Periodontal Pathogen.

Boswellia sacra Flueck. oleoresin extract (frankincense) has traditionally been used in the treatment of different diseases, but there are no sufficient studies on its potential activity against periodontal pathogens. Therefore, antibacterial and antibiofilm activity of frankincense extract against Porphyromonas gingivalis clinical isolates were studied. The phytochemical composition of the volatile components of the extract was identified by GC-MS analysis revealing 49 compounds as trans-nerolidyl formate, cycloartenol acetate, ursenoic acid 3-oxomethyl ester, bisabolene epoxide, and kaur-16-ene. It decreased the growth and increased the leakage of nucleotides in 58.3% and 33.3% of isolates, respectively. Additionally, it reduced the extracellular polysaccharide production and the cell surface hydrophobicity in 41.67% and 50% of the isolates, respectively. Crystal violet assay revealed inhibition of biofilm formation by the tested isolates. Light microscope and scanning electron microscope were used to examine the biofilms and they confirmed the reduction of biofilm formation by frankincense extract. Downregulation of the genes linked to biofilm formation (fimA, hagA, and hagB) was observed using qRT-PCR after treatment with the frankincense extract. This study suggested that the frankincense extract could exhibit antibacterial and antibiofilm activity against P. gingivalis isolates. Thus, the frankincense extract could be used as a treatment approach for periodontitis.

Inhibitory effects of sodium new houttuyfonate on growth and biofilm formation of Streptococcus mutans

The present study aimed to assess the impact of sodium new houttuyfonate (SNH) on growth and biofilm formation of Streptococcus mutans, and the combinatorial effects of SNH with cariostatic agents. The effects of SNH on S. mutans planktonic cultures were assessed by growth curve assay. The effects of SNH on S. mutans biofilm and extracellular polysaccharides (EPS) production were observed via crystal violet (CV) assay, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay, colony-forming unit (CFU) counting assay, scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM). Quantitative real-time polymerase chain reaction (qPCR) was applied to investigate the regulatory effects of SNH on the expression of virulence genes of S. mutans. Checkerboard microdilution assay was performed to investigate the combinatorial effects of SNH with two common cariostatic agents. SNH acted as an inhibitor on planktonic cell growth, biofilm formation and EPS production of S. mutans. SNH also downregulated the expression of gtfBCD and comDE systems and exhibited synergism with chlorhexidine (CHX). In conclusion, this study indicated a possibility for SNH to become an anticaries agents by its antimicrobial activity and synergistic effects with CHX against S. mutans.

Synonymous point mutation of gtfB gene caused by therapeutic X-rays exposure reduced the biofilm formation and cariogenic abilities of Streptococcus mutans

BackgroundThe shift of oral microbiota is a critical factor of radiation caries in head and neck cancer patients after the radiotherapy. However, the direct effects of irradiation on the genome and virulence of cariogenic bacteria are poorly described. Here we investigated the genomic mutations and virulence change of Streptococcus mutans (S. mutans), the major cariogenic bacteria, exposed to the therapeutic doses of X-rays.ResultsX-ray reduced the survival fraction of S. mutans and impacted its biofilm formation. We isolated a biofilm formation-deficient mutant #858 whose genome only possessed three synonymous mutations (c.2043 T > C, c.2100C > T, c.2109A > G) in gtfB gene. The “silent mutation” of c.2043 T > C in gtfB gene can cause the down-regulation of all of the gtfs genes’ expression and decrease the GtfB enzyme secretion without the effect on the growth due to the codon bias. #858 and synonymous point mutation strain gtfB2043 T>C, similar to the gtfB gene null mutant Δ gtfB, can significantly decrease the extracellular polysaccharide production, biofilm formation and cariogenic capabilities both in vitro and in vivo compared with wild type.ConclusionThe direct exposure of X-ray radiation can affect the genome and virulence of oral bacteria even at therapeutic doses. The synonymous mutations of genome are negligent factors for gene expression and related protein translation due to the codon usage frequency.

Probiotic Properties and Potentiality of Lactiplantibacillus plantarum Strains for the Biological Control of Chalkbrood Disease

Ascosphaera apis is an entomopathogenic fungus that affects honeybees. In stressful conditions, this fungus (due not only to its presence, but also to the combination of other biotic and abiotic stressors) can cause chalkbrood disease. In recent years, there has been increasing attention paid towards the use of lactic acid bacteria (LAB) in the honeybees’ diets to improve their health, productivity and ability to resist infections by pathogenic microorganisms. The screening of 22 strains of Lactiplantibacillus plantarum, isolated from the gastrointestinal tracts of honeybees and beebread, led to the selection of five strains possessing high antagonistic activity against A. apis. This study focused on the antifungal activity of these five strains against A. apis DSM 3116 and DSM 3117 using different matrices: cell lysate, broth culture, cell-free supernatant and cell pellet. In addition, some functional properties and the antioxidant activity of the five L. plantarum strains were evaluated. All five strains exhibited high antagonistic activity against A. apis, good surface cellular properties (extracellular polysaccharide (EPS) production and biofilm formation) and antioxidant activity. Although preliminary, these results are encouraging, and in future investigations, the effectiveness of these bacteria as probiotics in honeybee nutrition will be tested in vivo in the context of an eco-friendly strategy for the biological control of chalkbrood disease.

Core Microbiota Promotes the Development of Dental Caries

A previous longitudinal study about using microbiome as a caries indicator has successfully predicted early childhood caries (ECC) in healthy individuals, but there is no evidence to verify the composition of core microbiota and its pathogenicity in vitro and in vivo. Biofilm acidogenicity, S. mutans count, and biofilm composition were estimated by pH evaluation, colony-forming unit, and quantitative PCR, respectively. Extracellular polysaccharide production and enamel demineralization were observed by confocal laser scanning microscopy (CLSM) and transverse microradiography (TMR), respectively. A rat caries model was established for dental caries formation in vivo, and caries lesions were quantified by Keyes Scoring. We put forward that microbiota including Veillonella parvula, Fusobacterium nucleatum, Prevotella denticola, and Leptotrichia wadei served as the predictors for ECC may be the core microbiota in ECC. This study found that the core microbiota of ECC produced limited acid, but promoted growth and acidogenic ability of S. mutans. Besides, core microbiota could help to promote the development of biofilms. Moreover, the core microbiota enhanced the enamel demineralization in vitro and increased cariogenic potential in vivo. These results proved that core microbiota could promote the development of dental caries and plays an important role in the development of ECC.

Novel amide derivatives containing an imidazo[1,2-a]pyridine moiety: Design, synthesis as potential nematicidal and antibacterial agents

To discover new nematicides, a series of novel amide derivatives containing an imidazo[1,2-a]pyridine moeity were designed and synthesized. Among the title compounds, compounds 3 and 27 exhibited good nematicidal activities against Aphelenchoides besseyi (rice white-tip nematode), with LC50 values against of 27.3 and 35.9 mg/L, respectively, which were superior to that of fosthiazate (45.4 mg/L). Meanwhile, the LC50 value of compound 27 against Caenorhabditis elegans was 5.7 mg/L, which was superior to that of fosthiazate (77.2 mg/L). Compound 27 not only binds well to acetylcholinesterase (AChE) of nematodes, but also has a good inhibitory activity against AChE. Thus, AChE may be a potential target of compound 27 against nematodes. Unexpectedly, compound 28 exhibited excellent antibacterial activities with EC50 values of 1.2 and 3.1 mg/L against Xanthomonas oryzae pv. oryzae (Xoo) and Xanthomonas oryzae pv. oryzicola (Xoc), respectively, which were superior to those of bismerthiazol (68.6 and 77.1 mg/L) and thiodiazole copper (80.8 and 96.6 mg/L). The curative and protective activities of compound 28 against bacterial leaf blight were 37.0% and 36.8% at 50 mg/L, respectively, which were higher than those of thiodiazole copper (16.1% and 15.5%). In addition, compound 28 may inhibit the growth of Xoo by affecting the production of cell membranes and extracellular polysaccharides. Amide derivatives containing an imidazo[1,2-a]pyridine moeity can be used as good lead–structures to discover new nematicidal and antibacterial agents in the future.

Methane in wastewater treatment plants: status, characteristics, and bioconversion feasibility by methane oxidizing bacteria for high value-added chemicals production and wastewater treatment

Methane is a type of renewable fuel that can generate many types of high value-added chemicals, however, besides heat and power production, there is little methane utilization in most of the wastewater treatment plants (WWTPs) all round the world currently. In this review, the status of methane production performance from WWTPs was firstly investigated. Subsequently, based on the identification and classification of methane oxidizing bacteria (MOB), the key enzymes and metabolic pathway of MOB were presented in depth. Then the production, extraction and purification process of high value-added chemicals, including methanol, ectoine, biofuel, bioplastic, methane protein and extracellular polysaccharides, were introduced in detail, which was conducive to understand the bioconversion process of methane. Finally, the use of methane in wastewater treatment process, including nitrogen removal, emerging contaminants removal as well as resource recovery was extensively explored. These findings could provide guidance in the development of sustainable economy and environment, and facilitate biological methane conversion by using MOB in further attempts.