Role of the Nla6S and Nla28S histidine kinases in fruiting body development of \u3ci\u3eMyxococcus xanthus\u3c/i\u3e

The complex life cycle of Myxococcus xanthus makes it a model organism for studying multicellular developmental processes in bacteria. In response to adverse environmental conditions, M. xanthus aggregates and forms multicellular structures known as fruiting bodies. Two component signal transduction systems (TCS) are widely used by bacteria to detect and respond to environmental cues by regulating large-scale changes in gene expression. They contain a histidine kinase sensor that detects environmental cues and a response regulator that modulates cellular processes. Two key regulators of the early stages of fruiting body development are the Nla6S/Nla6 and Nla28S/Nla28 TCSs. The response regulators of these TCSs, Nla6 and Nla28, are important for the successful completion of fruiting body formation. However, the histidine kinase sensors that modulate the activity of these key response regulators were previously unknown. Here we report the identification and characterization of the Nla6S and Nla28S histidine kinases. Analysis of Nla6S reveals that it represents a new family of bacterial histidine kinases. Furthermore, it plays an important role in the M. xanthus life cycle. Analysis of Nla28S shows that this is an important sensor of early developmental events. Our data suggests that Nla28S is involved in sensing the two important events of early development, nutrient depletion and cell density. In response to these signals Nla28S regulates sporulation of M. xanthus. Characterization of Nla6S and Nla28S expands our knowledge of the signaling networks that regulate initiation of the multicellular developmental process of M. xanthus

GcsR, a TyrR-Like Enhancer-Binding Protein, Regulates Expression of the Glycine Cleavage System in Pseudomonas aeruginosa PAO1

ABSTRACT Glycine serves as a major source of single carbon units for biochemical reactions within bacterial cells. Utilization of glycine is tightly regulated and revolves around a key group of proteins known as the glycine cleavage system (GCS). Our lab previously identified the transcriptional regulator GcsR (PA2449) as being required for catabolism of glycine in the opportunistic pathogen Pseudomonas aeruginosa PAO1. In an effort to clarify and have an overall better understanding of the role of GcsR in glycine metabolism, a combination of transcriptome sequencing and electrophoretic mobility shift assays was used to identify target genes of this transcriptional regulator. It was found that GcsR binds to an 18-bp consensus sequence (TGTAACG-N4-CGTTCCG) upstream of the gcs2 operon, consisting of the gcvH2, gcvP2, glyA2, sdaA, and gcvT2 genes. The proteins encoded by these genes, namely, the GCS (GcvH2-GcvP2-GcvT2), serine hydroxymethyltransferase (GlyA2), and serine dehydratase (SdaA), form a metabolic pathway for the conversion of glycine into pyruvate, which can enter the central metabolism. GcsR activates transcription of the gcs2 operon in response to glycine. Interestingly, GcsR belongs to a family of transcriptional regulators known as TyrR-like enhancer-binding proteins (EBPs). Until this study, TyrR-like EBPs were only known to function in regulating aromatic amino acid metabolism. GcsR is the founding member of a new class of TyrR-like EBPs that function in the regulation of glycine metabolism. Indeed, homologs of GcsR and its target genes are present in almost all sequenced genomes of the Pseudomonadales order, suggesting that this genetic regulatory mechanism is a common theme for pseudomonads. IMPORTANCE Glycine is required for various cellular functions, including cell wall synthesis, protein synthesis, and the biosynthesis of several important metabolites. Regulating levels of glycine metabolism allows P. aeruginosa to maintain the metabolic flux of glycine through several pathways, including the metabolism of glycine to produce other amino acids, entry into the trichloroacetic acid cycle, and the production of virulence factors such as hydrogen cyanide. In this study, we characterized GcsR, a transcriptional regulator that activates the expression of genes involved in P. aeruginosa PAO1 glycine metabolism. Our work reveals that GcsR is the founding member of a novel class of TyrR-like EBPs that likely regulate glycine metabolism in Pseudomonadales

Cloning and heterologous expression of a novel subgroup of class IV polyhydroxyalkanoate synthase genes from the genus <i>Bacillus</i>

<p>Many microorganisms harbor genes necessary to synthesize biodegradable plastics known as polyhydroxyalkanoates (PHAs). We surveyed a genomic database and discovered a new cluster of class IV PHA synthase genes (<i>phaRC</i>). These genes are different in sequence and operon structure from any previously reported PHA synthase. The newly discovered PhaRC synthase was demonstrated to produce PHAs in recombinant <i>Escherichia coli</i>.</p