Probing the ArcA regulon in the rumen bacterium Mannheimia succiniciproducens by genome-wide expression profiling

Diversification of signal identity and modus operandi of the Haemophilus influenzae PAS-less ArcB sensor kinase

Bacteria employ two-component signal transduction systems (TCS) to sense environmental fluctuations and adjust their cellular functions. The Arc TCS is crucial for facultative anaerobes as it enables adaptation to varying respiratory conditions. The Escherichia coli ArcB detects redox changes through two cysteine amino acid residues within its PAS domain. However, the ArcB homologs from most bacteria belonging to the Pasteurellaceae family, lack the entire PAS domain, and in consequence the two regulatory cysteine amino acid residues. In this study, we show that the PAS-less ArcB of Haemophilus influenzae regulates its activity via a cysteine-independent mechanism, and we provide data suggesting that it responds to metabolic signals rather than redox cues. Thus, these two ArcB orthologs sense distinct signals and their regulatory mechanism rely on different molecular events. Our findings reveal divergent evolutionary trajectories of these ArcB homologs, despite the overall conservation of protein components, providing an example of how evolution has shaped different sensing strategies in bacteria.

Environmental adaptation and diversification of bacterial two-component systems

Bacterial two-component systems (TCS) are versatile signaling mechanisms that govern cellular responses to diverse environmental cues. These systems rely on phosphoryl-group transfers between histidine- and aspartate-containing modules of sensor histidine kinase and response regulator proteins. TCS diversity is shaped by the ecological niche of the bacterium, resulting in significant population-level variations. Consequently, orthologous TCSs can display considerable divergence throughout the signaling process. Here, we venture into the mechanisms governing the emergence of TCS variation, and explore the adaptation of orthologous TCS in bacteria with dissimilar lifestyles. The peculiar features of the bacterial adaptive response A/ultraviolet light repair Y (BarA/UvrY) and anoxic redox control B/anoxic redox control A (ArcB/ArcA) and their ortholog TCSs illustrate the remarkable capacity of TCSs to evolve and finely tune their signaling mechanisms, effectively addressing specific environmental challenges.

The ArcAB Two-Component System: Function in Metabolism, Redox Control, and Infection

ArcAB, also known as the Arc system, is a member of the two-component system family of bacterial transcriptional regulators and is composed of sensor kinase ArcB and response regulator ArcA. In this review, we describe the structure and function of these proteins and assess the state of the literature regarding ArcAB as a sensor of oxygen consumption. The bacterial quinone pool is the primary modulator of ArcAB activity, but questions remain for how this regulation occurs. This review highlights the role of quinones and their oxidation state in activating and deactivating ArcB and compares competing models of the regulatory mechanism. The cellular processes linked to ArcAB regulation of central metabolic pathways and potential interactions of the Arc system with other regulatory systems are also reviewed. Recent evidence for the function of ArcAB under aerobic conditions is challenging the long-standing characterization of this system as strictly an anaerobic global regulator, and the support for additional ArcAB functionality in this context is explored. Lastly, ArcAB-controlled cellular processes with relevance to infection are assessed.

The CpxRA two-component system is involved in the maintenance of the integrity of the cell envelope in the rumen bacterium Mannheimia succiniciproducens

In this study, we characterized the CpxRA two-component signal transduction system of the rumen bacterium Mannheimia succiniciproducens. The truncated form of the CpxA sensor kinase protein without its transmembrane domain was able to autophosphorylate and transphosphorylate the CpxR response regulator protein in vitro. We identified 152 putative target genes for the Cpx system in M. succiniciproducens, which were differentially expressed by more than twofold upon overexpression of the CpxR protein. Genes of a putative 16-gene operon related to the cell wall and lipopolysaccharide biosynthesis were induced strongly upon CpxR overexpression. The promoter region of the first gene of this operon, wecC encoding UDP-N-acetyl-D-mannosaminuronate dehydrogenase, was analyzed and found to contain a sequence homologous to the CpxR box of Escherichia coli. An electrophoretic mobility shift assay showed that the phosphorylated CpxR proteins were able to bind specifically to PCR-amplified DNA fragments containing the promoter sequence of wecC. Furthermore, a cpxR-disrupted mutant strain exhibited increased envelope permeability compared with a wild-type strain. These results suggest that the Cpx system of M. succiniciproducens is involved in the maintenance of the integrity of the cell envelope.