Stress preadaptation and overexpression of rpoS and hfq genes increase stress resistance of Pseudomonas fluorescens ATCC13525

Effects of chlorogenic acid-grafted-chitosan on biofilms, oxidative stress, quorum sensing and c-di-GMP in Pseudomonas fluorescens

This study determined the inhibitory mechanism as well as anti-biofilm activity of chlorogenic acid-grafted-chitosan (CS-g-CA) against Pseudomonas fluorescens (P. fluorescens) in terms of biofilm content, oxidative stress, quorum sensing and cyclic diguanosine monophosphate (c-di-GMP) concentration, and detected the changes in the expression levels of related genes by quantitative real-time PCR (qRT-PCR). Results indicated that treatment with sub-concentrations of CS-g-CA for P. fluorescens led to reduce the biofilm size of large colonies, decrease the content of biofilm and extracellular polymers, weaken the motility and adhesion of P. fluorescens. Moreover, CS-g-CA resulted in higher ROS levels, diminished catalase activity (CAT), and increased superoxide dismutase (SOD) in P. fluorescens. CS-g-CA reduced the production of quorum-sensing signaling molecules (AHLs) and the concentration of c-di-GMP in bacteria. Genes for flagellar synthesis (flgA), the resistance to stress (rpoS and hfq), and pde (phosphodiesterases that degrade c-di-GMP) were significantly down-regulated as determined by RT-PCR. Overall, CS-g-CA leads to the accumulation of ROS in bacteria via P. fluorescens environmental resistance genes and decreases the activity of enzymes in the bacterial antioxidant system, and interferes with the production and reception of quorum-sensing signaling molecules and the synthesis of c-di-GMP in P. fluorescens, which regulates the generation of biofilms.

Cold adapted Pseudomonas: ecology to biotechnology

The cold adapted microorganisms, psychrophiles/psychrotolerants, go through several modifications at cellular and biochemical levels to alleviate the influence of low temperature stress conditions. The low temperature environments depend on these cold adapted microorganisms for various ecological processes. The ability of the microorganisms to function in cold environments depends on the strategies directly associated with cell metabolism, physicochemical constrains, and stress factors. Pseudomonas is one among such group of microorganisms which is predominant in cold environments with a wide range of ecological and biotechnological applications. Bioformulations of Pseudomonas spp., possessing plant growth promotion and biocontrol abilities for application under low temperature environments, are well documented. Further, recent advances in high throughput sequencing provide essential information regarding the prevalence of Pseudomonas in rhizospheres and their role in plant health. Cold adapted species of Pseudomonas are also getting recognition for their potential in biodegradation and bioremediation of environmental contaminants. Production of enzymes and bioactive compounds (primarily as an adaptation mechanism) gives way to their applications in various industries. Exopolysaccharides and various biotechnologically important enzymes, produced by cold adapted species of Pseudomonas, are making their way in food, textiles, and pharmaceuticals. The present review, therefore, aims to summarize the functional versatility of Pseudomonas with particular reference to its peculiarities along with the ecological and biotechnological applications.

Improving NH3 and H2S removal efficiency with pilot-scale biotrickling filter by co-immobilizing Kosakonia oryzae FB2-3 and Acinetobacter baumannii L5-4

In this study, two NH₄⁺-N and S^2- removal strains, namely, Kosakonia oryzae (FB2-3) and Acinetobacter baumannii (L5-4), were isolated from the packing materials in a long-running biotrickling filter (BTF). The removal capacities of combined FB2-3 and L5-4 (FB2-3 + L5-4) toward 100 mg L^-1 of NH₄⁺-N and 200 mg L^-1 of S^2- reached 97.31 ± 1.62% and 98.57 ± 1.12% under the optimal conditions (32.0 °C and initial pH = 7.0), which were higher than those of single strain. Then, FB2-3 and L5-4 liquid inoculums were prepared, and their concentrations respectively reached 1.56 × 10⁹ CFU mL^-1 and 1.05 × 10⁹ CFU mL^-1 by adding different resuspension solutions and protective agents after 12-week storage at 25 °C. Finally, pilot-scale BTF test showed that NH₃ and H₂S in the real exhaust gases from a pharmaceutical factory were effectively removed with removal rates > 87% and maximum elimination capacities were reached 136 g (NH₃) m^-3 h^-1 and 176 g (H₂S) m^-3 h^-1 at 18 °C-34 °C and pH 4.0-7.0 in the BTF loaded with bamboo charcoal packing materials co-immobilized with FB2-3 and L5-4. After co-immobilization of FB2-3 and L5-4, in the bamboo charcoal packing materials, the new microbial diversity composition contained the dominant genera of Acinetobacter, Mycobacterium, Kosakonia, and Sulfobacillus was formed, and the diversity of entire bacterial community was decreased, compared to the control. These results indicate that FB2-3 and L5-4 have potential to be developed into liquid ready-to-use inoculums for effectively removing NH₃ and H₂S from exhaust gases in BTF.

Characterization of the RpoN regulon reveals the regulation of motility, T6SS2 and metabolism in Vibrio parahaemolyticus

Vibrio parahaemolyticus is a foodborne pathogen that can colonize the small intestine of the host and cause diarrhea. The alternative sigma factor RpoN plays a vital role in regulating motility, carbon utilization and affects host colonization in V. parahaemolyticus RIMD2210633. In this study, transcriptome and phenotypic analysis further expanded our understanding of the RpoN regulon in V. parahaemolyticus. A deletion mutant of rpoN (ΔrpoN) was subjected to RNA-seq for systemic identification of the RpoN-controlled genes. Compared with the wild-type (WT), 399 genes were differentially expressed in the ΔrpoN strain. Moreover, 264 genes were down-regulated in the ΔrpoN strain, including those associated with nitrogen utilization (VP0118), glutamine synthetase (VP0121), formate dehydrogenase (VP1511 and VP1513-VP1515), quorum sensing (opaR and luxZ), polar flagellar systems, and type VI secretion system 2 (T6SS2). Quantitative real-time reverse transcription PCR (qRT-PCR) and electrophoretic mobility shift assay (EMSA) further confirmed that RpoN could directly bind to the promoters of these genes associated with polar flagellar systems (flgB and fliE), lateral flagellar systems (flgB2 and lafA), T6SS2 (hcp2 and VPA1044) and glutamine synthetase (VP0121), and then positively regulate the expression of these systems. A RpoN-binding motif was identified in V. parahaemolyticus using the MEME suite and verified by the EMSA. Besides, the deletion of rpoN caused a significant decrease in hemolytic activity, adhesion, and cytotoxicity. Our results provide new cues to better understand the regulatory networks of RpoN protein to motility, T6SS2, and metabolism in V. parahaemolyticus.

Regulatory roles of RpoS in the biosynthesis of antibiotics 2,4-diacetyphloroglucinol and pyoluteorin of Pseudomonas protegens FD6

The rhizosphere microbe Pseudomonas protegens FD6 possesses beneficial traits such as the production of antibiotics like pyoluteorin (Plt) and 2,4-diacetylphloroglucinol (2,4-DAPG). The alternative RpoS (σ³⁸ factor), as a master regulator, activates or inhibits the transcription of stationary phase genes in several biocontrol organisms. Here, we investigated the complicated function and regulatory mechanism of RpoS in the biosynthesis of 2,4-DAPG and Plt in strain FD6. Phenotypic assays suggested that ΔrpoS was impaired in biofilm formation, swimming motility, swarming motility, and resistance to stress, such as heat, H₂O₂ and 12% ethanol. The RpoS mutation significantly increased both 2,4-DAPG and Plt production and altered the transcription and translation of the biosynthetic genes phlA and pltL, indicating that RpoS inhibited antibiotic production by FD6 at both the transcriptional and translational levels. RpoS negatively controlled 2,4-DAPG biosynthesis and transcription of the 2,4-DAPG operon phlACBD by directly interacting with the promoter sequences of phlG and phlA. In addition, RpoS significantly inhibited Plt production and the expression of its operon pltLABCDEFG by directly binding to the promoter regions of pltR, pltL and pltF. Further analyzes demonstrated that a putative R147 mutation in the RpoS binding domain abolished its inhibitory activity on the expression of pltL and phlA. Overall, our results reveal the pleiotropic regulatory function of RpoS in P. protegens FD6 and provide the basis for improving antibiotic biosynthesis by genetic engineering in biocontrol organisms.

Contrasting genome patterns of two pseudomonas strains isolated from the date palm rhizosphere to assess survival in a hot arid environment

The plant growth-promoting rhizobacteria (PGPRs) improve plant growth and fitness by multiple direct (nitrogen fixation and phosphate solubilization) and indirect (inducing systematic resistance against phytopathogens, soil nutrient stabilization, and maintenance) mechanisms. Nevertheless, the mechanisms by which PGPRs promote plant growth in hot and arid environments remain poorly recorded. In this study, a comparative genome analysis of two phosphate solubilizing bacteria, Pseudomonas atacamensis SM1 and Pseudomonas toyotomiensis SM2, isolated from the rhizosphere of date palm was performed. The abundance of genes conferring stress tolerance (chaperones, heat shock genes, and chemotaxis) and supporting plant growth (plant growth hormone, root colonization, nitrogen fixation, and phosphate solubilization) were compared among the two isolates. This study further evaluated their functions, metabolic pathways, and evolutionary relationship. Results show that both bacterial strains have gene clusters required for plant growth promotion (phosphate solubilization and root colonization), but it is more abundant in P. atacamensis SM1 than in P. toyotomiensis SM2. Genes involved in stress tolerance (mcp, rbs, wsp, and mot), heat shock, and chaperones (hslJ and hslR) were also more common in P. atacamensis SM1. These findings suggest that P. atacamensis SM1could have better adaptability to the hot and arid environment owing to a higher abundance of chaperone genes and heat shock proteins. It may promote plant growth owing to a higher load of root colonization and phosphate solubilization genes and warrants further in vitro study.

Differential Chromosome- and Plasmid-Borne Resistance of Escherichia coli hfq Mutants to High Concentrations of Various Antibiotics

The Hfq protein is a bacterial RNA chaperone, involved in many molecular interactions, including control of actions of various small RNA regulatory molecules. We found that the presence of Hfq was required for survival of plasmid-containing Escherichia coli cells against high concentrations of chloramphenicol (plasmid p27cmr), tetracycline (pSC101, pBR322) and ampicillin (pBR322), as hfq⁺ strains were more resistant to these antibiotics than the hfq-null mutant. In striking contrast, production of Hfq resulted in low resistance to high concentrations of kanamycin when the antibiotic-resistance marker was chromosome-borne, with deletion of hfq resulting in increasing bacterial survival. These results were observed both in solid and liquid medium, suggesting that antibiotic resistance is an intrinsic feature of these strains rather than a consequence of adaptation. Despite its major role as RNA chaperone, which also affects mRNA stability, Hfq was not found to significantly affect kan and tet mRNAs turnover. Nevertheless, kan mRNA steady-state levels were higher in the hfq-null mutant compared to the hfq⁺ strain, suggesting that Hfq can act as a repressor of kan expression.This observation does correlate with the enhanced resistance to high levels of kanamycin observed in the hfq-null mutant. Furthermore, dependency on Hfq for resistance to high doses of tetracycline was found to depend on plasmid copy number, which was only observed when the resistance marker was expressed from a low copy plasmid (pSC101) but not from a medium copy plasmid (pBR322). This suggests that Hfq may influence survival against high doses of antibiotics through mechanisms that remain to be determined. Studies with pBR322Δrom may also suggest an interplay between Hfq and Rom in the regulation of ColE1-like plasmid replication. Results of experiments with a mutant devoid of the part of the hfq gene coding for the C-terminal region of Hfq suggested that this region, as well as the N-terminal region, may be involved in the regulation of expression of antibiotic resistance in E. coli independently.