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Acidithiobacillus caldus is a typical extreme acidophile widely used in the biohydrometallurgical industry, which often experiences extreme environmental stress in its natural habitat. Hfq, an RNA-binding protein, typically functions as a global regulator involved in various cellular physiological processes. Yet, the biological functions of Hfq derived from such extreme acidophile have not been extensively investigated. In this study, the recombinant strain Δhfq/Achfq, constructed by CRISPR/Cas9-mediated chromosome integration, fully or partially restored the phenotypic defects caused by hfq deletion in Escherichia coli, including impaired growth performance, abnormal cell morphology, impaired swarming motility, decreased stress resistance, decreased intracellular ATP and free amino acid levels, and attenuated biofilm formation. Particularly noteworthy, the intracellular ATP level and biofilm production of the recombinant strain were increased by 12.2% and 7.0%, respectively, compared to the Δhfq mutant. Transcriptomic analysis revealed that even under heterologous expression, AcHfq exerted global regulatory effects on multiple cellular processes, including metabolism, environmental signal processing, and motility. Finally, we established a potential working model to illustrate the regulatory mechanism of AcHfq in bacterial resistance to environmental stress., (© 2024. The Author(s), under exclusive licence to Springer Nature B.V.)

Avian pathogenic Escherichia coli (APEC) is a subgroup of extra-intestinal pathogenic E. coli (ExPEC) strains that cause avian colibacillosis, resulting in significant economic losses to the poultry industry worldwide. It has been reported that a few two-component signal transduction systems (TCS) participate in the regulation of the virulence factors of APEC infection. In this study, a basSR -deficient mutant strain was constructed from its parent strain APECX40 (WT), and high-throughput sequencing (RNA-seq) was performed to analyse the transcriptional profile of WT and its mutant strain XY1. Results showed that the deletion of basSR down-regulated the transcript levels of a series of biofilm- and virulence-related genes. Results of biofilm formation assays and bird model experiments indicated that the deletion of basSR inhibited biofilm formation in vitro and decreased bacterial virulence and colonization in vivo . In addition, electrophoretic mobility shift assays confirmed that the BasR protein could bind to the promoter regions of several biofilm- and virulence-related genes, including ais , opgC and fepA . This study suggests that the BasSR TCS might be a global regulator in the pathogenesis of APEC infection. RESEARCH HIGHLIGHTS Transcriptional profiling showed that BasSR might be a global regulator in APEC. BasSR increases APEC pathogenicity in vivo . BasSR positively regulates biofilm- and the virulence-associated genes. BasSR can bind to the promoter regions of virulence-associated genes ais , opgC and fepA .

Microbes are evolutionarily robust organisms capable of rapid adaptation to complex stress, which enables them to colonize harsh environments. In nature, microbes are regularly challenged by starvation, which is a particularly complex stress because resource limitation often co-occurs with changes in pH, osmolarity, and toxin accumulation created by metabolic waste. Often overlooked are the additional complications introduced by eventual resource replenishment, as successful microbes must withstand rapid environmental shifts before swiftly capitalizing on replenished resources to avoid invasion by competing species. To understand how microbes navigate trade-offs between growth and survival, ultimately adapting to thrive in environments with extreme fluctuations, we experimentally evolved 16 Escherichia coli populations for 900 days in repeated feast/famine conditions with cycles of 100-day starvation before resource replenishment. Using longitudinal population-genomic analysis, we found that evolution in response to extreme feast/famine is characterized by narrow adaptive trajectories with high mutational parallelism and notable mutational order. Genetic reconstructions reveal that early mutations result in trade-offs for biofilm and motility but trade-ups for growth and survival, as these mutations conferred positively correlated advantages during both short-term and long-term culture. Our results demonstrate how microbes can navigate the adaptive landscapes of regularly fluctuating conditions and ultimately follow mutational trajectories that confer benefits across diverse environments. • Evolutionary outcomes differ based on duration and amplitude of feast and famine • Extreme feast/famine cycles confine adaptation and results in mutational order • Mutations in transcription regulators break trade-offs between growth and survival Cells frequently navigate both the rigors of starvation and resource variability. By experimentally evolving Escherichia coli populations in repeated extreme feast/famine cycles, Behringer and Ho et al. identify adaptive mutations breaking the evolutionary tension between survival and fast growth, a widely acknowledged paradigm in the literature. [ABSTRACT FROM AUTHOR]

Poor high salt stress resistance remained as a main hurdle limiting the efficient bio-based succinic acid production. In this study, the metabolically engineered E. coli not only showed improvement of high salt stress tolerance through expression of a global regulator IrrE, but also could use seawater for succinic acid fermentation. The recombinant strain showed an increased 1.20-fold of cell growth rate and 1.24-fold of succinic acid production. Expression levels of genes related glucose uptake and succinic acid synthesis were up-regulated, and more glycerol and trehalose were accumulated. Moreover, no significant differences were observed in cell growth even when tap water was replaced by 60% artificial seawater. In the fermentation using Yellow Sea seawater, 24.5 g/L succinic acid was achieved with a yield of 0.88 g/g. This strategy set up a platform for improving abiotic stress tolerances and provide a possible approach for fermentation processes with low cost. [ABSTRACT FROM AUTHOR]

The electrochemical activity of electroactive bacteria is unique and essential for bioelectrochemical systems (BES) with promising energy and environment applications. However, the strategies for bacterial electrochemical activity modulation are still limited. Herein, a novel approach for engineering of bacterial electrochemical activity with global regulator (sigma factor RpoS) manipulation was developed. By knockout of rpoS in Pseudomonas aeruginosa PAO1, the biofilm formation on the electrode was enhanced and the bacterial cells were adapted to a new electron shuttle, which promoted the extracellular electron transfer and improved the performance of BES. This work demonstrated that global regulator manipulation could be efficient for electrochemical activity engineering and offered new opportunities for BES applications. [ABSTRACT FROM AUTHOR]

Cronobacter sakazakii is a Gram-negative opportunistic pathogen that causes necrotizing enterocolitis, sepsis, and meningitis in premature infants. The genetic basis of C. sakazakii virulence is poorly understood. In this study, the putative LysR-type transcriptional regulator (LTTR) gene (ESA_01081 homolog) was characterized as a possible regulator for C. sakazakii pathogenesis. An in-frame deletion mutant of the ESA_01081 homolog and its cognate complementation strain were constructed and characterized for pathogenesis (adhesion/invasion potentials to human intestinal cells and in vivo rat pup challenge assay), biofilm formation, resistance to oxidative stress and induction of IL-8 secretion. LTTR-deficient C. sakazakii ATCC 29544 exhibits significantly attenuated phenotypes in all the properties tested, except adhesion. Our data strongly suggest that the putative gpESA_01081 homolog, plays an important regulatory role in diverse biological processes including the virulence of C. sakazakii. This is the first report of a functional global regulator in C. sakazakii. [ABSTRACT FROM AUTHOR]

Cyclic (5′ to 3′)-diguanosine monophosphate (c-di-GMP) is a small molecule that regulates the transition between the sessile and motile lifestyle, an integrative part of biofilm formation and other multicellular behavior, in many bacteria. The recognition of c-di-GMP as a novel secondary messenger soon raised the question about the specificity of the signaling system, as individual bacterial genomes frequently encode numerous c-di-GMP metabolizing proteins. Recent work has demonstrated that several global regulators concertedly modify the expression of selected panels of c-di-GMP metabolizing proteins, which act on targets with physiological functions. Within complex feed-forward arrangements, the global regulators commonly combine the control of c-di-GMP metabolism with the direct regulation of proteins with functions in motility or biofilm formation, leading to precise and fine-tuned output responses that determine bacterial behavior, c-di-GMP metabolizing proteins are also controlled at the post- translational level by mechanisms including phosphorylation, localization, protein-protein interactions or protein stability. A detailed understanding of such complex regulatory mechanisms will not only help to explain the specificity in c-di-GMP signaling systems, but will also be necessary to understand the high phenotypic diversity within bacterial biofilms at the single cell level. [ABSTRACT FROM AUTHOR]

Aeromonas hydrophila is an important aquatic microorganism that can cause fish hemorrhagic septicemia. In this study, we identified a novel LysR family transcriptional regulator (LahS) in the A. hydrophila Chinese epidemic strain NJ-35 from a library of 947 mutant strains. The deletion of lahS caused bacteria to exhibit significantly decreased hemolytic activity, motility, biofilm formation, protease production, and anti-bacterial competition ability when compared to the wild-type strain. In addition, the determination of the fifty percent lethal dose (LD50) in zebrafish demonstrated that the lahS deletion mutant (ΔlahS) was highly attenuated in virulence, with an approximately 200-fold increase in LD50 observed as compared with that of the wild-type strain. However, the ΔlahS strain exhibited significantly increased antioxidant activity (six-fold). Label-free quantitative proteome analysis resulted in the identification of 34 differentially expressed proteins in the ΔlahS strain. The differentially expressed proteins were involved in flagellum assembly, metabolism, redox reactions, and cell density induction. The data indicated that LahS might act as a global regulator to directly or indirectly regulate various biological processes in A. hydrophila NJ-35, contributing to a greater understanding the pathogenic mechanisms of A. hydrophila. [ABSTRACT FROM AUTHOR]