Nutrient-limited Conditions Research Articles

Plant growth-promoting Bacillus amyloliquefaciens orchestrate homeostasis under nutrient deficiency exacerbated drought and salinity stress in Oryza sativa L. seedlings.

Nutrient deficiency intensifies drought and salinity stress on rice growth. Bacillus amyloliquefaciens inoculation provides resilience through modulation in metabolic and gene regulation to enhance growth, nutrient uptake, and stress tolerance. Soil nutrient deficiencies amplify the detrimental effects of abiotic stresses, such as drought and salinity, creating substantial challenges for overall plant health and crop productivity. Traditional methods for developing stress-resistant varieties are often slow and labor-intensive. Previously, we demonstrated that plant growth-promoting rhizobacteria Bacillus amyloliquefaciens strain SN13 effectively alleviates stress induced by sub-optimum nutrient conditions in rice. In this study, we evaluated the effectiveness of SN13 in reducing the compounded impacts of drought and salinity under varying nutrient regimes in rice seedlings. The results demonstrated that PGPR inoculation not only improved the growth parameters, nutrient content, and physio-biochemical characteristics under nutrient-limited conditions, but also reduced the oxidative stress markers. The altered expression of stress-related and transcription factor genes (USP, DEF, CYP450, GST, MYB, and bZIP) revealed the regulatory effect of PGPR in enhancing stress tolerance through these genes. GC-MS-based untargeted metabolomic analysis revealed that PGPR significantly influenced various metabolic pathways, including galactose metabolism, fructose and mannose metabolism, and fatty acid biosynthesis pathways, suggesting that PGPR affects both energy production and stress-protective mechanisms, facilitating better growth and survival of rice seedlings.

Glucose limitation protects cancer cells from apoptosis induced by pyrimidine restriction and replication inhibition.

Cancer cells often experience nutrient-limiting conditions because of their robust proliferation and inadequate tumour vasculature, which results in metabolic adaptation to sustain proliferation. Most cancer cells rapidly consume glucose, which is severely reduced in the nutrient-scarce tumour microenvironment. In CRISPR-based genetic screens to identify metabolic pathways influenced by glucose restriction, we find that tumour-relevant glucose concentrations (low glucose) protect cancer cells from inhibition of de novo pyrimidine biosynthesis, a pathway that is frequently targeted by chemotherapy. We identify two mechanisms to explain this result, which is observed broadly across cancer types. First, low glucose limits uridine-5-diphosphate-glucose synthesis, preserving pyrimidine nucleotide availability and thereby prolonging the time to replication fork stalling. Second, low glucose directly modulates apoptosis downstream of replication fork stalling by suppressing BAK activation and subsequent cytochrome c release, key events that activate caspase-9-dependent mitochondrial apoptosis. These results indicate that the low glucose levels frequently observed in tumours may limit the efficacy of specific chemotherapeutic agents, highlighting the importance of considering the effects of the tumour nutrient environment on cancer therapy.

In Vivo Quantification of Surfactin Nonribosomal Peptide Synthetase Complexes in Bacillus subtilis.

Surfactin, a potent biosurfactant produced by Bacillus subtilis, is synthesized using a non-ribosomal peptide synthetase (NRPS) encoded by the srfAA-AD operon. Despite its association with quorum sensing via the ComX pheromone, the dynamic behavior and in vivo quantification of the NRPS complex remain underexplored. This study established an in vivo quantification system using fluorescence labeling to monitor the availability of surfactin-forming NRPS subunits (SrfAA, SrfAB, SrfAC, and SrfAD) during bioprocesses. Four Bacillus subtilis sensor strains were constructed by fusing these subunits with the megfp gene, resulting in strains BMV25, BMV26, BMV27, and BMV28. These strains displayed growth and surfactin productivity similar to those of the parental strain, BMV9. Fluorescence signals indicated varying NRPS availability, with BMV27 showing the highest and BMV25 showing the lowest relative fluorescence units (RFUs). RFUs were converted to the relative number of NRPS molecules using open-source FPCountR package. During bioprocesses, NRPS availability peaked at the end of the exponential growth phase and declined in the stationary phase, suggesting reduced NRPS productivity under nutrient-limited conditions and potential post-translational regulation. This study provides a quantitative framework for monitoring NRPS dynamics in vivo, offering insights into optimizing surfactin production. The established sensor strains and quantification system enable the real-time monitoring of NRPS availability, aiding bioprocess optimization for industrial applications of surfactin and potentially other non-ribosomal peptides.

Global Profiling of Protein Phosphorylation, Acetylation, and β-Hydroxybutyrylation in Nannochloropsis oceanica.

Protein post-translational modifications (PTMs) regulate protein functions but remain poorly characterized in Nannochloropsis. This study examined three PTMs: lysine acetylation (Kac), lysine β-hydroxybutyrylation (Kbhb), and phosphorylation. Using LC-MS/MS, we identified 4571 Kac sites, 7812 Kbhb sites, and 6237 phosphorylation sites across 2455, 3109, and 2786 proteins, respectively. Subcellular localization analysis revealed significant overlaps between Kac and Kbhb proteins, primarily in the chloroplast, cytosol, and nucleus, while phosphorylated proteins were predominantly located in the nucleus and chloroplast. Motif analysis highlighted specific amino acid enrichments around modification sites, with several motifs conserved. Additionally, 529 proteins harbored all three PTMs, underscoring the potential regulatory interplay. Kac, Kbhb, and phosphorylated proteins were particularly abundant in glycolysis, the TCA cycle, carbon fixation, and lipid metabolism pathways, influencing energy production and lipid accumulation. Based on previous transcriptome data under nutrient-limited conditions, these frequently modified key enzymes appear to be vital components in the response to abiotic stress. The presence of histone modifications related to Kac and Kbhb might also point to the epigenetic regulation in gene expression and stress adaptation. This comprehensive PTM landscape in N. oceanica provides a foundation of valuable insights into future metabolic engineering and biotechnological applications.

Mapping Active RNA Polymerases in Proliferating and Quiescent Fission Yeast Cells Using Precision Run-On Sequencing.

The development of next-generation sequencing (NGS) approaches to investigate the functioning of RNA polymerases has led to groundbreaking advances in the field of transcriptional regulation. One powerful method, Precision nuclear Run-On sequencing (PRO-seq), maps the locations of RNA polymerase active sites genome-wide at high resolution. PRO-seq provides a snapshot of strand-specific transcriptional activity and does not rely on immunoprecipitation of the polymerase of interest. Notably, this technique has been utilized to investigate the control of the RNA polymerase II transcription cycle in a variety of model systems. However, the initially published PRO-seq method required significant amounts of starting sample and was technically challenging, both of which were deterrents for its broader use. Recently, an improved and simplified version called qPRO-seq that reduced the length of the experiment and the quantity of necessary input sample was developed for human and Drosophila cell lines. Here we provide an updated, step-by-step protocol in which we have validated and optimized qPRO-seq for the fission yeast Schizosaccharomyces pombe. Importantly, we have implemented this method for assessing RNA polymerase activity in nutrient-limiting conditions, for both proliferating and nitrogen-depleted quiescent cells.

A conserved two-component system senses intracellular iron levels and regulates redox balance in Mycobacterium spp.

For bacteria, an intricate coordination between sensing and regulating iron levels and managing oxidative stress is required as their levels are tightly interlinked. While various oxidative stress and heme-based redox sensors have been reported for both pathogenic and non-pathogenic bacteria, the mechanisms governing the modulation of intracellular iron levels in response to changes in redox status remain unclear. In this study, a gene-inactivated strain of mycobacterial sensor kinase PdtaS showed dysregulated expression of genes associated with iron metabolism, including Fe-S clusters, NADH dehydrogenases, and iron uptake. The strain showed poor growth in nutrient-limiting conditions, a defect rescuable by heme but not by Fe3+ supplementation. This observation was associated with the PAS domain of the PdtaS sensor kinase. Biochemical and biophysical experiments established heme-binding to the PAS domain and its inhibitory effect on PdtaS auto-kinase activity, suggesting that the absence of heme induces activation of this sensor kinase. Interestingly, despite having an endogenous heme biosynthetic pathway or even external heme supplementation, the ∆pdtaS mutant exhibited persistent low intracellular iron levels concomitant with elevated oxidative stress. Antioxidant supplementation mitigated growth defects, emphasizing the link between oxidative stress, intracellular iron levels, and PdtaS activity. RNA-IP identified key targets associated with redox homeostasis and iron metabolism as targets of the PdtaR response regulator. The study proposes a novel role for the PdtaS-PdtaR TCS in sensing heme, regulation of intracellular iron levels, and redox balance.IMPORTANCEThe research article investigates the intricate interplay between bacteria's ability to take and utilize iron without inducing excess iron's toxic effects, including oxidative stress. The study shows that bacteria achieve this by sensing intracellular iron available as heme through a sensory protein PdtaS, which turns off when heme is in excess and prevents iron uptake and iron efflux. The process shields bacteria from generating Fe-dependent free radicals and allows it to maintain viability. The absence of sensor kinase abrogates all these processes, increasing bacteria susceptibility to ROS and thereby slowing growth. This feature of the sensor kinase PdtaS makes it an attractive co-therapeutic target for tuberculosis therapy, where its inhibition will prevent iron uptake, even in the presence of low iron, thereby halting bacterial proliferation.

Metarhizium fight club: Within-host competitive exclusion and resource partitioning.

Both Metarhizium robertsii ARSEF 2575 (Mr2575) and Metarhizium anisopliae ARSEF 549 (Ma549) infect a range of insects whilst also interacting with plants; however, little is known about the traits that affect the competitive ability of different strains. We examined the interactions between Mr2575 and Ma549 in culture and during co-infection of plants (Arabidopsis thaliana) and insects. Mr2575 outcompetes Ma549 under nutrient-limiting conditions, including root exudates, giving it a priority advantage on Arabidopsis roots. However, during co-infection of Manduca sexta or Drosophila melanogaster, Ma549's higher blastospore production enhanced its competitive ability within the host. In large M. sexta (fifth instar), blastospores facilitate dispersal, suppress host melanization and prevent Mr2575 from spreading from infection sites, reducing conidia production. However, colonization of smaller hosts such as first instar M. sexta and D. melanogaster did not provide Ma549 with a competitive advantage, as conidial production was dependent on retaining control of the cuticle through which conidiating hyphae emerge. Unexpectedly, Ma549 and Mr2575 segregate within hosts, suggesting resource partitioning with Mr2575 predominating in the thoraxes of Drosophila, especially in females, and Ma549 in the abdomen. In fifth instar M. sexta, Mr2575 was most prevalent around spiracles and the front end of segments, despite Ma549 and Mr2575 having similar susceptibility to hypoxia. Dispersing conidia homogeneously into the hemocoel of fifth instar M. sexta eliminated the blastospore production advantage, making Ma549 and Mr2575 equally competitive, with strict partitioning of Mr2575 at the anterior and Ma549 at the posterior ends of segments. As Metarhizium species have multiple roles in natural ecosystems and agroecosystems these discoveries are relevant to understanding their impact on maintaining biodiversity and for exploiting them to enhance food security.

Substrate identification of putative NCS1 and NCS2 nucleobase transporters in Pseudomonas aeruginosa.

Pseudomonas aeruginosa is a frequently multidrug-resistant opportunistic pathogen and one of the most common causes of healthcare-acquired infections. While nucleobases are known to support growth in nutrient-limited conditions, recent work showed that adenine and hypoxanthine can also decrease P. aeruginosa biofilm formation by disrupting c-di-GMP metabolism. Thus, nucleobase transport may be relevant to multiple aspects of P. aeruginosa biology and pathogenesis. However, there is currently little known about the transport of nucleobases in P. aeruginosa. Our work reports initial substrate identifications for 10 putative nucleobase transporters in P. aeruginosa, providing new tools to address previously difficult-to-test hypotheses relating to nucleobase transport in this organism.

Independent and interactive effects of N and P additions on foliar P fractions in evergreen forests of southern China

Fertilization or atmospheric deposition of nitrogen (N) and phosphorus (P) to terrestrial ecosystems can alter soil N (P) availability and the nature of nutrient limitation for plant growth. Changing the allocation of leaf P fractions is potentially an adaptive strategy for plants to cope with soil N (P) availability and nutrient-limiting conditions. However, the impact of the interactions between imbalanced anthropogenic N and P inputs on the concentrations and allocation proportions of leaf P fractions in forest woody plants remains elusive. We conducted a meta-analysis of data about the concentrations and allocation proportions of leaf P fractions, specifically associated with individual and combined additions of N and P in evergreen forests, the dominant vegetation type in southern China where the primary productivity is usually considered limited by P. This assessment allowed us to quantitatively evaluate the effects of N and P additions alone and interactively on leaf P allocation and use strategies. Nitrogen addition (exacerbating P limitation) reduced the concentrations of leaf total P and different leaf P fractions. Nitrogen addition reduced the allocation to leaf metabolic P but increased the allocation to other fractions, while P addition showed opposite trends. The simultaneous additions of N and P showed an antagonistic (mutual suppression) effect on the concentrations of leaf P fractions, but an additive (summary) effect on the allocation proportions of leaf P fractions. These results highlight the importance of strategies of leaf P fraction allocation in forest plants under changes in environmental nutrient availability. Importantly, our study identified critical interactions associated with combined N and P inputs that affect leaf P fractions, thus aiding in predicting plant acclimation strategies in the context of intensifying and imbalanced anthropogenic nutrient inputs.

Impact of Nutrient Starvation on Biofilm Formation in Pseudomonas aeruginosa: An Analysis of Growth, Adhesion, and Spatial Distribution.

Objectives: This study investigates the impact of nutrient availability on the growth, adhesion, and biofilm formation of Pseudomonas aeruginosa ATCC 27853 under static conditions. Methods: Bacterial behaviour was evaluated in nutrient-rich Luria-Bertani (LB) broth and nutrient-limited M9 media, specifically lacking carbon (M9-C), nitrogen (M9-N), or phosphorus (M9-P). Bacterial adhesion was analysed microscopically during the transition from reversible to irreversible attachment (up to 120 min) and during biofilm production/maturation stages (up to 72 h). Results: Results demonstrated that LB and M9 media supported bacterial growth, whereas nutrient-starved conditions halted growth, with M9-C and M9-N inducing stationary phases and M9-P leading to cell death. Fractal analysis was employed to characterise the spatial distribution and complexity of bacterial adhesion patterns, revealing that nutrient-limited conditions affected both adhesion density and biofilm architecture, particularly in M9-C. In addition, live/dead staining confirmed a higher proportion of dead cells in M9-P over time (at 48 and 72 h). Conclusions: This study highlights how nutrient starvation influences biofilm formation and bacterial dispersion, offering insights into the survival strategies of P. aeruginosa in resource-limited environments. These findings should contribute to a better understanding of biofilm dynamics, with implications for managing biofilm-related infections and industrial biofouling.

Histone-like transcription factor Hfl1p in Candida albicans harmonizes nuclear and mitochondrial genomic network in regulation of energy metabolism and filamentation development

ABSTRACT Candida albicans is an opportunistic fungal pathogen known for surviving in various nutrient-limited conditions within the host and causing infections. Our prior research revealed that Hfl1p, an archaeal histone-like or Hap5-like protein, is linked to mitochondrial ATP generation and yeast-hyphae morphogenesis. However, the specific roles of Hfl1p in these virulence behaviours, through its function in the CBF/NF-Y complex or as a DNA polymerase II subunit, remain unclear. This study explores Hfl1p’s diverse functions in energy metabolism and morphogenesis. By combining proteomic analysis and phenotypic evaluations of the hfl1Δ/hfl1Δ mutant with ChIP data, we found that Hfl1p significantly impacts mitochondrial DNA-encoded CI subunits, the tricarboxylic acid (TCA) cycle, and morphogenetic pathways. This influence occurs either independently or alongside other transcription factors recognizing a conserved DNA motif (TAXXTAATTA). These findings emphasize Hfl1p’s critical role in linking carbon metabolism and mitochondrial respiration to the yeast-to-filamentous form transition, enhancing our understanding of C. albicans’ metabolic adaptability during morphological transition, an important pathogenic trait of this fungus. This could help identify therapeutic targets by disrupting the relationship between energy metabolism and cell morphology in C. albicans.

Toxin-mediated depletion of NAD and NADP drives persister formation in a human pathogen

Toxin–antitoxin (TA) systems are widespread in bacteria and implicated in genome stability, virulence, phage defense, and persistence. TA systems have diverse activities and cellular targets, but their physiological roles and regulatory mechanisms are often unclear. Here, we show that the NatR–NatT TA system, which is part of the core genome of the human pathogen Pseudomonas aeruginosa, generates drug-tolerant persisters by specifically depleting nicotinamide dinucleotides. While actively growing P. aeruginosa cells compensate for NatT-mediated NAD+ deficiency by inducing the NAD+ salvage pathway, NAD depletion generates drug-tolerant persisters under nutrient-limited conditions. Our structural and biochemical analyses propose a model for NatT toxin activation and autoregulation and indicate that NatT activity is subject to powerful metabolic feedback control by the NAD+ precursor nicotinamide. Based on the identification of natT gain-of-function alleles in patient isolates and on the observation that NatT increases P. aeruginosa virulence, we postulate that NatT modulates pathogen fitness during infections. These findings pave the way for detailed investigations into how a toxin–antitoxin system can promote pathogen persistence by disrupting essential metabolic pathways.

Effect of Amorphous Halomonas-PHB on Growth, Body Composition, Immune-Related Gene Expression and Vibrio anguillarum Resistance of Hybrid Grouper (Epinephelus fuscoguttatus ♀ × E. lanceolatu ♂) Juveniles.

Poly-β-hydroxybutyrate (PHB) is a bacterial metabolite produced by bacteria such as Halomonas sp. that serves as a carbon and energy storage compound for bacteria under nutrient-limited conditions. Two experiments were conducted to investigate the effects of dietary supplementation with Halomonas-PHB on hybrid grouper (Epinephelus fuscoguttatus ♀ × E. lanceolatu ♂). In experiment I, juvenile groupers were fed basal diets supplemented with 3% Halomonas-PHB (3% HM-PHB) containing 1.4% PHB and 3% Halomonas (3% HM) without PHB, as well as a control diet, for seven weeks. The results showed no significant difference in survival rate, weight gain, and crude fat content between the 3% HM-PHB group and the control group; however, the crude protein of the 3% HM-PHB group was significantly lower than that of the control group. Furthermore, supplementation with 3% HM-PHB increased the fatty acids content in fish muscles, including long-chain unsaturated fatty acids C18:1n9, EPA, and DHA. In experiment II, groupers were fed a basal diet supplemented with 6.5% Halomonas-PHB (6.5% HM-PHB) containing 3% PHB and 6.5% Halomonas (6.5% HM) containing no PHB, as well as a basal diet (Control). After seven weeks of rearing, the fish were challenged with Vibrio anguillarum for 48 h. Although no significant difference in survival rate and growth was observed among different groups, the dietary supplement of 6.5% Halomonas-PHB improved the survival rate of V. anguillarum challenged grouper and significantly increased the gene expressions of catalase (CAT) and superoxide dismutase (SOD) in blood, interleukin 1 (IL1) and interleukin 10 (IL10) in the liver, spleen, head kidney, and blood (p < 0.05). In conclusion, dietary supplementation of Halomonas-PHB had no significantly positive effect on fish growth performance but increased the content of fatty acids, including long-chain unsaturated fatty acids C18:1n9, EPA, and DHA in fish muscle; it also improved the V. anguillarum resistance, possibly through increasing immune-related gene expression in different tissues and organs. Our findings offer compelling evidence that Halomonas-PHB can be utilized as a feed additive in intensive grouper farming to enhance the groupers' resistance to Vibrio.

Effects of nutrient ratios on a newly harmful dinoflagellate Heterocapsa bohaiensis: Evidence from growth, toxicity and transcriptome analyses

Heterocapsa bohaiensis is a newly identified dinoflagellate species that causes harmful blooms in coastal areas in China, Malaysian, and New Caledonian. These blooms have led to substantial economic losses for local aquaculture. Previous studies have mainly focused on understanding the toxicity of H. bohaiensis. However, the causes of H. bohaiensis blooms remain unknown. In this study, we aimed to ascertain nitrogen (N) and phosphorus (P) requirements for the growth and reproduction of H. bohaiensis. Additionally, we sought to understand the functional mechanisms by comparing the transcriptomes of H. bohaiensis under nutrient-limited conditions and control conditions. The results revealed a wide range of acceptable N:P ratios for H. bohainensis, attributed to a mechanism involving nutrient storage, which allowed H. bohainensis to sustain its growth even when either nitrate or phosphate was depleted. Higher N:P ratios (>27.5) were more conducive to the growth of H. bohainensis than f/2 medium or low ratios, which is related to the N:P ratios absorbed by H. bohainensis. The toxicity of H. bohainensis was significantly enhanced in N-limited or P-limited states. These findings underscore the significance of the physiological metabolism of H. bohainensis in adapting to environmental stresses induced by human activities and establishing the dominance of blooms.

Two-step polyhydroxybutyrate production from hydrogenic effluent by freshwater microalgae Coelastrella sp. KKU-P1 and Acutodesmus sp. KKU-P2 under mixotrophic cultivation

This study aimed to produce PHB using hydrogenic effluent discharged from the biohydrogen production process with freshwater microalgae including Coelastrella sp. KKU-P1, and Acutodesmus sp. KKU-P2. Batch experiments explored the influence of initial pH and hydrogenic effluent concentration, revealing optimal conditions at 10 % (v/v) effluent concentration and a pH of 6.5 for both KKU-P1 and KKU-P2. Subsequently, medium formulation and photoperiods were optimized to maximize biomass and PHB accumulation. The results showed that the optimal condition for PHB accumulation with KKU-P1 and KKU-P2 was nitrogen phosphorus (NP)-limited Bold's Basal Medium (BBM) under dark conditions. A two-step PHB accumulation in the upscale bioreactor was investigated under optimal conditions. The results showed that KKU-P1 achieved maximum PHB, protein, carbohydrate, and lipid contents of 4.57 %, 29.37 %, 24.76 %, and 13.21 %, respectively, whereas KKU-P2 achieved 6.35 %, 31.53 %, 16.16 %, and 4.77 %, respectively. Based on these findings, it appears that a mixotrophic approach under nutrient-limiting conditions is effective for PHB production in both KKU-P1 and KKU-P2 strains.

Nitrogen Nutrition-Induced Changes in Macronutrient Content and Their Indirect Effect on N-Metabolism Via an Impact on Key N-Assimilating Enzymes in Bread Wheat (Triticum aestivum L.)

Judicious application of nitrogen (N) fertilizers in crop production is critical for reducing the nitrate pollution of groundwater and greenhouse gas emissions. It is, thus, important to improve the nitrogen use efficiency under the reduced application of nitrogen. A genotypic variation in N-uptake and N-use efficiency particularly under low N-input conditions exists across crops that can be deciphered and exploited for environmentally sustainable farming without any significant penalty of yield and quality. The present research conducted under the nutrient solution culture aimed to explore the inherent variability in the growth response of ten genetically diverse wheat varieties to low fertilizer N-application (N-, 10 μM N) in comparison to N sufficient control (N+, 8.5 mM N) viz., a viz., the activity of various key N-assimilating enzymes and to delineate the indirect effect of low N on uptake and partitioning of other major macronutrients viz., P, K, S, which may indirectly regulate the N-use efficiency. A notable increase in sulfur, potassium, and phosphorus content was observed under nitrogen-deficient conditions. Varieties such as Carnamah and HD 2824 exhibit a significant increase in shoot phosphorus content, emphasizing their potential to optimize phosphorus acquisition and utilization efficiency under nutrient-limited conditions. The findings highlight the complex interplay between nutrient availability and plant responses, showcasing varietal-specific adaptations to nitrogen limitations.

Induction and comparative resuscitation of viable but nonculturable state on Vibrio parahaemolyticus serotypes O3:K6 and O1:K25.

Vibrio parahaemolyticus, an important food-borne pathogens found to be associated with seafoods and marine environs. It has been a topic of debate for many decades that most pathogens are known to enter a viable but nonculturable (VBNC) state under cold temperature and nutrient limited conditions. The present study examined the time required for the induction of VBNC state and the revival strategies of both the endemic O3:K6 and O1:K25 sporadic strains of V. parahaemolyticus. The results revealed that V. parahaemolyticus survived even after 55 days of incubation in nutrient starved media such as phosphate buffered saline (PBS) and Coastal Water (CW) and could be recovered by temperature upshift method, and compared the resuscitation using Dulbecco's Modified Eagle Medium (DMEM), sheep blood serum, chitin flakes with live Artemia salina, and the results suggests that chitin plays a significant role in regulating the VBNC state. It was also confirmed by Confocal Laser Scanning Microscopy (CLSM) and Scanning Electron Microscope (SEM) analysis that VBNC cells can alter their morphology to coccoid forms in order to survive in most extreme nutrient limited environment. Further data on the promoting factors and the exact mechanism that resuscitate VBNC V. parahaemolyticus in cold natural environments and frozen foods are needed to perform a robust risk assessment.

Effect of mutation of phaC on carbon supply, extracellular polysaccharide production, and pathogenicity of Xanthomonas oryzae pv. oryzae

Xanthomonas oryzae pv. oryzae (Xoo) causes bacterial blight in rice. Polyhydroxyalkanoates (PHAs) consitute a diverse group of biopolyesters synthesized by bacteria under nutrient-limited conditions. The phaC gene is important for PHA polymerization. We investigated the effects of phaC gene mutagensis in Xoo strain PXO99A. The phaC gene knock-out mutant exhibited reduced swarming ability relative to that of the wild-type. Under conditions where glucose was the sole sugar source, extracellular polysaccharide (EPS) production by ΔphaC declined by 44.8%. ΔphaC showed weak hypersensitive response (HR) induction in the leaves of non-host Nicotiana tabacum, concomitant with downregulation of hpa1 gene expression. When inoculated in rice leaves by the leaf-clipping method, ΔphaC displayed reduced virulence in terms of lesion length compared with the wild-type strain. The complemented strain showed no significant difference from the wild-type strain, suggesting that the deletion of phaC in Xoo induces significant alterations in various physiological and biological processes. These include bacterial swarming ability, EPS production, transcription of hrp genes, and glucose metabolism. These changes are intricately linked to the energy utilization and virulence of Xoo during plant infection. These findings revealed involvement of phaC in Xoo is in the maintaining carbon metabolism by functioning in the PHA metabolic pathway.

Regulation of TCA cycle genes by srbA sRNA: Impacts on Pseudomonas aeruginosa virulence and survival

Pseudomonas aeruginosa, an opportunistic bacterial pathogen of public health concern, is known for its metabolic versatility, adaptability in harsh environment, and pathogenic aggressiveness. P. aeruginosa relies on various regulatory networks modulated by small non-coding RNAs, which in turn influence different physiological traits such as metabolism, stress response, and pathogenesis. In this study, srbA sRNA has been shown to play a diverse role in regulating cellular metabolism and the production of different virulence factors in P. aeruginosa. srbA was found to control the TCA cycle, a key regulatory pathway for cellular metabolism and energy production, by regulating three main enzymes: citrate synthase (gltA), isocitrate dehydrogenase (icd), and α-ketoglutarate dehydrogenase E1 subunit (sucA) at both the transcriptional and translational levels. By modulating the TCA cycle, srbA could help the bacteria to adapt nutritional stress by lowering energy consumption. Additionally, srbA has been found to differentially regulate production of various virulence factors such as rhamnolipid, elastase, LasA protease, and pyocyanin under both nutrient-rich and nutrient-limiting conditions. It could also influence motilities in P. aeruginosa, linked to biofilm formation and pathogenicity. Thus, srbA might hold a promise in the research area for identifying virulence pathways and developing novel therapeutic targets to combat the global pathogenic threat of P. aeruginosa.

Microbial Primer: what is the stringent response and how does it allow bacteria to survive stress?

The stringent response is a conserved bacterial stress response that allows bacteria to alter their activity and survive under nutrient-limiting conditions. Activation of the stringent response is characterized by the production of intracellular signalling molecules, collectively termed (p)ppGpp, which interact with multiple targets inside bacterial cells. Together, these interactions induce a slow growth phenotype to aid bacterial survival by altering the transcriptomic profile of the cell, inhibiting ribosome biosynthesis and targeting enzymes involved in other key metabolic processes.