Microbiology China is supervised by Chinese Academy of Sciences, sponsored by Chinese Society for Microbiology and Institute of Microbiology, CAS.
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[Background] The wastewater discharged by coal chemical industry contains a large number of refractory and highly toxic organic pollutants. It is an economically feasible strategy to treat the wastewater with bioaugmentation technology based on effective degrading bacteria. Promoting the biofilm formation of degrading bacteria is proved to be beneficial to the performance of the biofilm wastewater treatment system. [Objective] To investigate the biofilm formation process and characteristics of a pyridine-degrading bacterium
Pseudomonas sp. ZX08, and to identify the influence of different environmental factors such as temperature, pH, Na
+, K
+, Ca
2+, and Mg
2+ on biofilm formation, and finally to provide reference for regulating biofilm formation in wastewater treatment systems. [Methods] A modified microtiter dish biofilm formation assay was used to determine the biofilm formation and the planktonic bacteria growth in the 12-well plate under different conditions; the structural characteristics of biofilm was observed using a confocal laser scanning microscope (CLSM). [Results]
Pseudomonas sp. ZX08 showed good pyridine-degrading performance and biofilm-forming abilities. According to the CLSM analysis, the thickness of its biofilms formed at the surface reached 40–50 μm, and the proportion of live cells and protein/cell ratio were higher in the outer layer of the biofilms. A periodic variation was observed in the biofilm formation process in 72 h, and the biofilm biomass at the time points of 12 h and 48 h were relative peaks. The optimum temperature for ZX08 biofilm formation was 25°C, and the optimum pH range was 7.0–9.0. Higher concentrations of NaCl (> 0.6 mol/L) and KCl (> 0.4 mol/L) significantly inhibited the biofilm formation of ZX08. Within a certain range (0–16 mmol/L), the increase of Ca
2+ concentration could promote the biofilm formation at the solid-liquid interface of the 12-well plate bottom. Adding 0–16 mmol/L Mg
2+ also led to a slight increase in the biofilm formation of ZX08. [Conclusion] The pyridine-degrading bacterium
Pseudomonas sp. ZX08 can form thick and stable biofilm, and it needs to comprehensively consider the influence of environmental factors on the biofilm formation of this strain in the future application.
[Background] Bacterial community diversity affected the composting process and biochar influenced the growth of bacteria. However, the effect of biochar on the bacterial community structure for pig manure composting has not been reported yet. [Objective] According to the variation of bacterial community structure and composting temperature, appropriate amount of biochar was added during pig manure composting to improve the proportion of major bacteria for composting and composting efficiency. Thus, this study provides a reference for the joint application of biochar and pig manure composting. [Methods] The biochar content of 0%, 3%, 6%, and 9% was set, and four levels of biochar were selected in the high-temperature period and the stable-temperature period of composting process, respectively. According to the result of Illumina MiSeq high-throughput sequencing of bacterial 16S rRNA, the effect of biochar content and composting temperature on bacterial community structure of pig manure composting was analyzed. [Results] At the phylum level, the bacteria with the highest abundance in pig manure composting were Proteobacteria, Actinobacteria, Bacteroidetes, Chloroflexi, Gemmatimonadetes, Firmicutes, Acidobacteria, and Deinococcus-Thermus. At the genus level, the bacteria with the highest abundance in pig manure composting were
Chryseolinea, Subgroup
_6
_norank,
Steroidobacter,
Anaerolineaceae,
Nonomuraea,
Longispora,
Bacillus,
Sporacetigenium,
Luteimonas,
Phyllobacteriaceae,
Truepera,
Rhodothermaceae, and
Aquamicrobium. The variation of biochar content could promote or inhibit the growth of major bacteria in pig manure composting. As the content of biochar increased, the abundance of
Bacillus,
Streptomyces,
Rhodothermaceae, and Firmicutes increased, whereas the abundance of
Chryseolinea,
Longispora, and
Steroidobacter decreased. In the high-temperature composting period, the abundance of Firmicutes,
Bacillus, and
Streptomyces was greater than that in the stable-temperature composting period, while that of Chloroflexi,
Anaerolineaceae, and
Longispora was lower than that in the stable-temperature composting period. The number of bacterial communities in high-temperature composting period was up to 70, significantly larger than that (15) in the stable-temperature composting period. Among them, the number of bacteria playing a major role in pig manure composting was up to 7 (Rhizobiales,
Incertae_Sedis, Proteobacteria, Alphaproteobacteria, Xanthomonadales, Gammaproteobacteria, and
Steroidobacter) in the high-temperature period, while only three (Micromonosporales,
Longispora and Micromonosporaceae) were found in the stable-temperature period. The bacterial diversity of pig manure composting in high-temperature period was significantly higher than that in stable-temperature period. After biochar was added to pig manure composting, environmental factors (electrical conductivity, water content, temperature, and pH) had no significant effect on the major bacteria of pig manure composting. β-Proteobacteria,
Rhodothermaceae,
Phyllobacteriaceae, and
Bacterium were significantly affected by the water content, temperature, and pH. [Conclusion] The content of biochar and composting temperature could change the bacterial community structure of pig manure composting and significantly increase the number and diversity of bacteria in pig manure composting in the high-temperature period. The electrical conductivity, water content, temperature, and pH of pig manure composting could affect the growth of composting bacteria, but the effect on bacteria with the highest abundance in pig manure composting was not significant.
[Background] Antimicrobial resistance of bacteria has become more and more serious due to the abuse of antimicrobials. As a major foodborne pathogen,
Vibrio parahaemolytics also exhibits a certain level of antimicrobial resitance. Quorum sensing system can regulate the antimicrobial resistance of bacteria, which provides a new pathway to study the mechanism and control technique of antimicrobial resistance of
V. parahaemolytics. [Objective] To study the effect of signaling molecule autoinducer-2 (AI-2) on tetracycline resistance of
V. parahaemolyticus strains from seafood. [Methods] AI-2 was synthesized
in vitro by a reaction using the critical enzymes, S-ribosylhomocysteinase (LuxS) and S-adenosylhomocysteine nucleosidase (Pfs), which were prepared by prokaryotic expression. The effect of AI-2 on tetracycline resistance of
V. parahaemolyticus was determined by colony counting method. The effect of AI-2 at different concentrations on the transcriptional levels of tetracycline resistance genes in
V. parahaemolyticus was assayed by reverse transcription and real-time quantitative PCR. [Results] LuxS and Pfs enzymes were obtained by prokaryotic expression. The bioactive AI-2 could be synthesized
in vitro by adding LuxS and Pfs to the substrate S-adenosylhomocysteine (SAH), with the fluorescence intensity of about 6 times as much as that of positive control. When treated with tetracycline at subinhibitory concentration, AI-2 could significantly promote the growth of
V. parahaemolyticus strains, and AI-2 at the concentrations of 6, 15 and 30 μmol/L could increase the transcriptional levels of tetracycline resistance genes in
V. parahaemolyticus strains to a certain extent. [Conclusion] AI-2 could enhance the tetracycline resistance of
V. parahaemolyticus, which provided a reference for further study on the antimicrobial resistance mechanism of
V. parahaemolyticus and developing control techniques targeting AI-2 on the antimicrobial resistance of
V. parahaemolyticus.
[Background] Small RNA EsrE affects cell growth by regulating the expression of succinate dehydrogenase in
Escherichia coli, and the exploration of its regulatory mechanism is conducive to the understanding of EsrE effect on cell growth. [Objective] To explore the transcriptional regulation mechanism of small RNA EsrE in
E. coli. [Methods] Transcriptional regulators were screened out using a dual-plasmid reporter system; the interaction between RpoH and P
esrE was verified by electrophoretic mobility shift assay (EMSA); qRT-PCR shows effects of the transcriptional regulators on EsrE. [Results] The results of reporter system demonstrated that RpoH up-regulated P
esrE and FabZ down-regulated P
esrE. The results of EMSAs showed that RpoH bound the P
esrE fragment directly, while FabZ did not. [Conclusion] RpoH is involved in the regulation of
esrE transcription by directly binding with the P
esrE promoter, while FabZ is involved in the transcriptional regulation of EsrE indirectly by other ways.
[Background] Cecropin is an extensively studied effective antimicrobial peptide, which has the potential of commercial production for the application in aquaculture and agriculture. [Objective] To obtain a genetically engineered strain for efficient production of cecropin AD. [Methods] The recombinant vector pGAPZαA-CAD was firstly constructed and then transformed to
P. pastoris X33 strain by electric shock. Cecropin AD gene was successfully expressed and X33/GCAD strain was obtained. Secondly, the recombinant vector pUCGAP-CAD was constructed and transformed into X33/GCAD strain. The pGAPZαA-CAD plasmid was integrated into the GAPDH promoter region of
P. pastoris X33 with Zeocin as resistance screening label, while pUCGAP-CAD plasmid was integrated into the non-translated rDNA region of
P. pastoris X33 with geneticin as resistance screening label. Finally, a recombinant X33/GUCAD strain with an efficiently expressed cecropin AD gene was obtained. [Results] The antimicrobial compound of X33/GUCAD was cecropin AD which was identified by mass spectrometry. Afterward optimizing its fermentation conditions, we found that the X33/GUCAD strain had a higher potential to express cecropin AD by consuming glycerol as a sole carbon source while peptone and yeast extract as organic nitrogen source. [Conclusion] The higher copy number is more beneficial to the increase of cecropin AD titer, and the engineered strain is more stable in the later fermentation process and suitable for industrial production.
