How Bacterial Pathogens Coordinate Appetite with Virulence

Bacterial metabolism in the host and its association with virulence

The host restricted pathogens are competently dependent on their respective host for nutritional requirements. The bacterial metabolic pathways are surprisingly varied and remarkably flexible that in turn help them to successfully overcome competition and colonise their host. The metabolic adaptation plays pivotal role in bacterial pathogenesis. The understanding of host-pathogen metabolic crosstalk needs to be prioritized to decipher host-pathogen interactions. The review focuses on various aspects of host pathogen interactions that majorly involves adaptation of bacterial metabolism to counteract immune mechanisms by rectifying metabolic cues that provides pathogen the idea of different anatomical sites and the local physiology of the host. The key set of metabolites that are recognized as centre of competition between host and its pathogens are also briefly discussed. The factors that control the timely expression of virulence of bacterial pathogens is poorly understood. The perspective presented herein will facilitate us with a broader view of molecular mechanisms that modulates the expression of virulence factors in bacterial pathogens. The knowledge of crosslinked metabolic pathways of bacteria and their host will serve to develop novel potential therapeutics.

Cytoplasmic Mg2+ supersedes carbon source preference to dictate Salmonella metabolism

Glucose is the preferred carbon source of most studied microorganisms. However, we now report that glucose loses preferred status when the intracellular pathogen Salmonella enterica serovar Typhimurium experiences cytoplasmic magnesium (Mg2+) starvation. We establish that this infection-relevant stress drastically reduces synthesis of cyclic adenosine monophosphate (cAMP), the allosteric activator of the cAMP receptor protein (CRP), master regulator of carbon utilization. The resulting reduction in cAMP concentration, which is independent of carbon source, decreases transcription of CRP-cAMP-activated carbon utilization genes, hinders carbon source uptake, and restricts metabolism, rendering wild-type bacteria phenotypically CRP-. A cAMP-independent allele of CRP overcame the transcriptional, uptake, and metabolic restrictions caused by cytoplasmic Mg2+ starvation and significantly increased transcription of the glucose uptake gene when S. Typhimurium was inside murine macrophages. The reduced preference for glucose exhibited by S. Typhimurium inside macrophages reflects that transcription of the glucose uptake gene requires higher amounts of active CRP-cAMP than transcription of uptake genes for preferred carbon sources, such as gluconate and glycerol. By reducing CRP-cAMP activity, low cytoplasmic Mg2+ alters carbon source preference, adjusting metabolism and growth.

Tyrosine phosphorylation coupling of one carbon metabolism and virulence in an endogenous pathogen

Endogenous pathogens can constrain virulence to ensure survival in the host. Pathogenic state can be controlled by metabolic responses to the prevailing microenvironment; however, the coupling and effector mechanisms are not well understood. Flux through the One Carbon Metabolism (OCM) pathway can modulate virulence of the oral pathobiont Porphyromonas gingivalis , and here we show that this is controlled by tyrosine phosphorylation-dependent differential partitioning of gingipain proteases. The OCM essential precursor pABA inhibits the low molecular weight tyrosine phosphatase Ltp1, and consequently relieves inhibition of its cognate kinase, Ptk1. We found that in the absence of pABA, reduced Ptk1 kinase activity blocks extracellular release of gingipains. Surface retention of gingipains confers resistance to neutrophil mobilization and killing, and virulence in animal models of disease is elevated. Reciprocally, Ptk1 and gingipains are required for maximal flux through OCM, and Ptk1 can phosphorylate the OCM pathway enzymes GlyA and GcvT. Further, ALP, an alkaline phosphatase involved in synthesis of DHPPP, which combines with pABA to make DHP, is phosphorylated and activated by Ptk1. We propose, therefore, that although the primary function of Ptk1 is to maintain OCM balance, it mechanistically couples metabolism with tunable pathogenic potential through directing the location of proteolytic virulence factors.

Context-dependent change in the fitness effect of (in)organic phosphate antiporter glpT during Salmonella Typhimurium infection

Salmonella enterica is a frequent cause of foodborne diseases, which is attributed to its adaptability. Even within a single host, expressing a gene can be beneficial in certain infection stages but neutral or even detrimental in others as previously shown for flagellins. Mutants deficient for the conserved glycerol-3-phosphate and phosphate antiporter glpT have been shown to be positively selected in nature, clinical, and laboratory settings. This suggests that different selective pressures select for the presence or absence of GlpT in a context dependent fashion, a phenomenon known as antagonistic pleiotropy. Using mutant libraries and reporters, we investigated the fitness of glpT-deficient mutants during murine orogastric infection. While glpT-deficient mutants thrive during initial growth in the gut lumen, where GlpT's capacity to import phosphate is disadvantageous, they are counter-selected by macrophages. The dichotomy showcases the need to study the spatial and temporal heterogeneity of enteric pathogens' fitness across distinct lifestyles and niches. Insights into the differential adaptation during infection may reveal opportunities for therapeutic interventions.

Anthrax: Transmission, Pathogenesis, Prevention and Treatment

Bacillus anthracis is a deadly pathogen that under unfavourable conditions forms highly resistant spores which enable them to survive for a long period of time. Spores of B. anthracis are transmitted through the contaminated soil or animal products and enter to the host through the skin, lungs or oral route and can cause cutaneous, injection, inhalation and gastrointestinal anthrax, respectively. The disease is caused by the toxin which is produced by them once they germinate within the host cell. Anthrax toxin is the major virulence factor which has the ability to kill the host cell. The role of protein kinases and phosphatases of B. anthracis in toxin production and other virulence related properties have also been reported. There are two vaccines, BioThrax and CYFENDUSTM, which are approved by the FDA-USA to prevent anthrax disease. Recently, anthrax toxin has also been shown to be a potential candidate for cancer therapeutics. Through present review, we aim to provide insights into sporulation, transmission and pathogenesis of B. anthracis as well as the current state of its prevention, treatment, vaccines and possible therapeutic uses in cancer.

Metabolic tug-of-war: Microbial metabolism shapes colonization resistance against enteric pathogens

A widely recognized benefit of gut microbiota is that it provides colonization resistance against enteric pathogens. The gut microbiota and their products can protect the host from invading microbes directly via microbe-pathogen interactions and indirectly by host-microbiota interactions, which regulate immune system function. In contrast, enteric pathogens have evolved mechanisms to utilize microbiota-derived metabolites to overcome colonization resistance and increase their pathogenic potential. This review will focus on recent studies of metabolism-mediated mechanisms of colonization resistance and virulence strategies enteric pathogens use to overcome them, along with how induction of inflammation by pathogenic bacteria changes the landscape of the gut and enables alternative metabolic pathways. We will focus on how intestinal pathogens counteract the protective effects of microbiota-derived metabolites to illustrate the growing appreciation of how metabolic factors may serve as crucial virulence determinants and overcome colonization resistance.

Identification of a cellular role of hemolysin co-regulatory protein (Hcp) in Vibrio alginolyticus modulating substrate metabolism and biofilm formation by cAMP-CRP

Cyclic AMP (cAMP) and cAMP receptor protein (CRP) system controls catabolic enzyme expression based on metabolite concentrations in bacteria. Hemolysin co-regulatory protein (Hcp) is well known as a molecular chaperone for virulence factor secretion of the type VI secretion system (T6SS). However, the intracellular role of Hcp involving in bacterial physiological processes remains unknown. To clarify that, we constructed a single hcp mutant strain and analyzed their effects on the physiological processes of Vibrio alginolyticus. The omics results revealed the extensive involvement of Hcp in the catabolic metabolism in bacteria. Simultaneously, Hcp1 and Hcp2 played opposing regulatory roles on the bacterial growth, biofilm formation, and intracellular cAMP-CRP levels during cultivation in a glucose medium. Furthermore, the interacting protein screening and co-immunoprecipitation (Co-IP) assays confirmed that the glucose-specific phosphoenolpyruvate (PEP)-phosphotransferase system (PTS) enzyme IIA component (EIIAglc) was a key interacting partner with Hcp proteins as well as class I adenylyl cyclase (AC-I) in Vibrio alginolyticus. These results indicated that, to achieve cellular homeostasis, Hcp1 and Hcp2 might exert antagonistic and synergistic effects, respectively, on the interaction between EIIAglc and AC thus cooperatively regulating intracellular cAMP-CRP production.

Virulence regulation in plant-pathogenic bacteria by host-secreted signals

Bacterial pathogens manipulate host signaling pathways and evade host defenses using effector molecules, coordinating their deployment to ensure successful infection. However, host-derived metabolites as signals, and their critical role in regulating bacterial virulence requires further insights. Effective regulation of virulence, which is essential for pathogenic bacteria, involves controlling factors that enable colonization, defense evasion, and tissue damage. This regulation is dynamic, influenced by environmental cues including signals from host plants like exudates. Plant exudates, comprising of diverse compounds released by roots and tissues, serve as rich chemical signals affecting the behavior and virulence of associated bacteria. Plant nutrients act as signaling molecules that are sensed through membrane-localized receptors and intracellular response mechanisms in bacteria. This review explains how different bacteria detect and answer to secreted chemical signals, regulating virulence gene expression. Our main emphasis is exploring the recognition process of host-originated signaling molecules through molecular sensors on cellular membranes and intracellular signaling pathways. This review encompasses insights into how bacterial strains individually coordinate their virulence in response to various distinct host-derived signals that can positively or negatively regulate their virulence. Furthermore, we explained the interruption of plant defense with the perception of host metabolites to dampen pathogen virulence. The intricate interplay between pathogens and plant signals, particularly in how pathogens recognize host metabolic signals to regulate virulence genes, portrays a crucial initial interaction leading to profound influences on infection outcomes. This work will greatly aid researchers in developing new strategies for preventing and treating infections.

Mechanisms of host adaptation by bacterial pathogens

The emergence of new infectious diseases poses a major threat to humans, animals, and broader ecosystems. Defining factors that govern the ability of pathogens to adapt to new host species is therefore a crucial research imperative. Pathogenic bacteria are of particular concern, given dwindling treatment options amid the continued expansion of antimicrobial resistance. In this review, we summarize recent advancements in the understanding of bacterial host species adaptation, with an emphasis on pathogens of humans and related mammals. We focus particularly on molecular mechanisms underlying key steps of bacterial host adaptation including colonization, nutrient acquisition, and immune evasion, as well as suggest key areas for future investigation. By developing a greater understanding of the mechanisms of host adaptation in pathogenic bacteria, we may uncover new strategies to target these microbes for the treatment and prevention of infectious diseases in humans, animals, and the broader environment.

Determinants of bacterial survival and proliferation in blood

Bloodstream infection is a major public health concern associated with high mortality and high healthcare costs worldwide. Bacteremia can trigger fatal sepsis whose prevention, diagnosis, and management have been recognized as a global health priority by the World Health Organization. Additionally, infection control is increasingly threatened by antimicrobial resistance, which is the focus of global action plans in the framework of a One Health response. In-depth knowledge of the infection process is needed to develop efficient preventive and therapeutic measures. The pathogenesis of bloodstream infection is a dynamic process resulting from the invasion of the vascular system by bacteria, which finely regulate their metabolic pathways and virulence factors to overcome the blood immune defenses and proliferate. In this review, we highlight our current understanding of determinants of bacterial survival and proliferation in the bloodstream and discuss their interactions with the molecular and cellular components of blood.

The pig intestinal phageome is an important reservoir and transfer vector for virulence genes

Bacteriophages (phages) can significantly influence the composition and functions of their host communities, and enhance host pathogenicity via the transport of phage-encoded virulence genes. Phages are the main component of animal gut viruses, however, there are few reports on the piglet gut phageome and its contribution to virulence genes. Here, a total of 185 virulence genes from 59,955 predicted genes of gut phages in weaned piglets were identified, with 0.688 % of the phage contigs coding for at least one virulence gene. The virulence gene pblA was the most abundant, with various virulence genes significantly correlated with gut phages and their encoded mobile gene element (MGE) genes. Importantly, multiple virulence genes and MGE genes coexist in some phage sequences, and up to 12 virulence genes were detected in a single phage sequence, greatly increasing the risk of phage-mediated transmission of virulence genes into the bacterial genome. In addition, diarrhoea has driven changes in the composition and structure of phage and bacterial communities in the intestinal tract of weaned piglets, significantly increasing the abundance of phage contigs encoding both virulence genes and MGE genes in faecal samples, which potentially increases the risk of phage-mediated virulence genes being transfected into the gut bacterial genome. In summary, this study expands our understanding of the gut microbiome of piglets, advances our understanding of the potential role of phages in driving host pathogenesis in the gut system, and provides new insights into the sources of virulence genes and genetic evolution of bacteria in pig farm environments.