Abstract
Myxococcus xanthus is a gram-negative, soil-dwelling bacterium that undergoes development in response to depletion of nutrients. Whereas most cells aggregate into multicellular mounds in which they differentiate into spores, 10 to 20% of the developing cells remain outside fruiting bodies as peripheral rods. We used two-dimensional polyacrylamide gel electrophoresis to analyze the global expression of polypeptides in cells taken from six stages in the life cycle: vegetatively growing cells, cells 15 h after the induction of development, peripheral rods, prespores (sonication-sensitive, aggregated cells), fruiting-body spores (sonication-resistant, aggregated cells) 96 h after the induction of development, and glycerol-induced spores 15 h after induction. Seven hundred sixty-one discrete sample spots (SSPs) were identified among the six gels. Comparisons among the samples revealed that each sample had some unique SSPs, ranging from 0.3% of the 15-h developing cell SSPs to 17.9% of 96-h peripheral rod SSPs. Sixty-eight SSPs were ubiquitously distributed, but the relative amounts of these SSPs varied among the samples. Statistical analyses of the distribution and relative quantities of the SSPs indicate that, within a confidence level of greater than 99.99%, peripheral rods are significantly different from vegetatively growing cells, 15-h developing cells, prespores, fruiting-body spores, and glycerol-induced spores. In fact, among the six samples studied, only 15-h developing cells and glycerol-induced spores were similar to each other within a confidence level of P greater than or equal to 0.05. These results are consistent with the description of peripheral rods as a distinct developmental cell type.