Summary Social (S)-motility inMyxococcus xanthus is a flagellum-independent gliding motility system that allows bacteria to move in groups on solid surfaces. S-motility has been shown to require type IV pili (TFP), exopolysaccharide (EPS; a component of fibrils) and lipopolysaccharide (LPS). Previously, information concerning EPS biogenesis in M. xanthus was lacking. In this study, we screened 5000 randomly mutagenized colonies for defects in S-motility and EPS and identified two genetic regions essential for EPS biogenesis: the EPS synthesis ( eps ) region and the EPS -associated ( eas ) region. Mutants with insertions in the eps and eas regions were defective in Smotility and fruiting body formation. These mutants failed to bind the dye calcofluor white, indicating that they lacked EPS; however, they retained normal TFP and LPS. Analysis of the eps locus showed several open reading frames (ORFs) that encode homologues to glycosyltransferases, glucanases and EPS transporters as well as regulatory proteins; the eas locus contains two ORFs: one exhibits homology to hypothetical proteins with a conserved domain of unknown function and the other displays no apparent homology to other proteins in the database. Further genetic mutagenesis analysis indicates that the whole eps region is involved in the biosynthesis of fibrils and fibril EPS. The operon at the proximal end of the eps region was analysed by generating in-frame deletion mutations. These mutants showed varying degrees of defects in the bacterium's ability to produce EPS or perform EPS-related functions, confirming the involvement of these genes in M. xanthus EPS biogenesis.

The fruiting body development of Myxococcus xanthus consists of two separate but interacting pathways: one for aggregation of many cells to form raised mounds and the other for sporulation of individual cells into myxospores. Sporulation of individual cells normally occurs after mound formation, and is delayed at least 30 h after starvation under our laboratory conditions. This suggests that M. xanthus has a mechanism that monitors progress towards aggregation prior to triggering sporulation. A null mutation in a newly identified gene, espA (early sporulation), causes sporulation to occur much earlier compared with the wild type (16 h earlier). In contrast, a null mutation in an adjacent gene, espB, delays sporulation by about 16 h compared with the wild type. Interestingly, it appears that the espA mutant does not require raised mounds for sporulation. Many mutant cells sporulate outside the fruiting bodies. In addition, the mutant can sporulate, without aggregation into raised mounds, under some conditions in which cells normally do not form fruiting bodies. Based on these observations, it is hypothesized that EspA functions as an inhibitor of sporulation during early fruiting body development while cells are aggregating into raised mounds. The aggregation‐independent sporulation of the espA mutant still requires starvation and high cell density. The espA and espB genes are expressed as an operon and their translations appear to be coupled. Expression occurs only under developmental conditions and does not occur during vegetative growth or during glycerol‐induced sporulation. Sequence analysis of EspA indicates that it is a histidine protein kinase with a fork head‐associated (FHA) domain at the N‐terminus and a receiver domain at the C‐terminus. This suggests that EspA is part of a two‐component signal transduction system that regulates the timing of sporulation initiation.

Two new potent anti-Gram negative compounds, coralmycins A (1) and B (2), were isolated from cultures of the myxobacteria Corallococcus coralloides M23, together with another derivative (3) that was identified as the very recently reported cystobactamid 919-2. Their structures including the relative stereochemistry were elucidated by interpretation of spectroscopic, optical rotation, and CD data. The relative stereochemistry of 3 was revised to "S*R*" by NMR analysis. The antibacterial activity of 1 was most potent against Gram-negative pathogens, including Escherichia coli, Pseudomonas aeruginosa, Acinetobacter baumanii, and Klebsiella pneumoniae, with MICs of 0.1-4 μg/mL; these MICs were 4-10 and 40-100 times stronger than the antibacterial activities of 3 and 2, respectively. Thus, these data indicated that the β-methoxyasparagine unit and the hydroxy group of the benzoic acid unit were critical for antibacterial activity.

The Agrobacterium tumefaciens putA gene, which encodes proline dehydrogenase, is transcriptionally induced by exogenous proline. In contrast to the putA genes of enteric bacteria, the A. tumefaciens putA gene is not regulated by the PutA protein, as the putA promoter remained strongly proline inducible in strains lacking PutA. A putA null mutation increased the expression of the putA promoter under a variety of conditions. However, this mutation is predicted to increase the cytoplasmic concentration of proline, and this alone probably accounts for its effects on putA expression. The putA promoter was also strongly induced by valine, and the putA genotype did not affect expression by this gratuitous inducer. An open reading frame (ORF) encoding an Lrp-like protein was found transcribed divergently from putA. Disruption of this ORF, designated putR, abolished induction of the putA promoter by proline or valine. In addition to activating putA, PutR also repressed its own transcription, and this autorepression was only slightly affected by exogenous proline. The transcription start sites for the putA and putR genes are separated by 64 nucleotides, suggesting that PutR could regulate both promoters by binding to a single operator.

Myxococcus xanthus has a complex life cycle that includes fruiting body formation. One of the first stages in development has been called A‐signalling. The asg (A‐signalling) mutants have been proposed to be deficient in producing A‐signal, resulting in development arresting at an early stage. In this paper, we report the identification of a new asg locus asgD. This locus appears to be involved in both environmental sensing and intercellular signalling. Expression of asgD was undetected during vegetative growth, but increased dramatically within 1 h of starvation. The AsgD protein is predicted to contain 773 amino acids and to be part of a two‐component regulatory system because it has a receiver domain located at the N‐terminus and a histidine protein kinase at the C‐terminus. An asgD null mutant was defective in fruiting body formation and sporulation on CF medium. However, the defects of the mutant were complemented extracellularly when cells were mixed with wild‐type strains or with bsgA, csgA, dsgA or esgA mutants, but were not complemented extracellularly by asgA, asgB or asgC mutants. In addition, the mutant was rescued by a subset of A‐factor amino acids. Surprisingly, when the mutant was plated on stringent starvation medium rather than CF, cells were able to form fruiting bodies. Thus, it appears that AsgD is directly or indirectly involved in sensing nutritionally limiting conditions. The discovery of the asgD locus provides an important sensory transduction component of early development in M. xanthus.