How Bacterial Pathogens Coordinate Appetite with Virulence

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.

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.

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.