Induction of beta-lactamase influences the course of development in Myxococcus xanthus

Myxococcus xanthus is a gram-negative bacterium that develops in response t o starvation on a solid surface. The cells assemble into multicellular aggr egates in which they differentiate from rod-shaped cells into spherical, en vironmentally resistant spores. Previously, we have shown that the inductio n of beta-lactamase is associated with starvation-independent sporulation i n liquid culture (K. A. O'Connor and D. R. Zusman, Mel. Microbiol, 24:839-8 50, 1997), In this paper, we show that the chromosomally encoded beta-lacta mase of M. xanthus is autogenously induced during development. The specific activity of the enzyme begins to increase during aggregation, before spore s are detectable. The addition of inducers of beta-lactamase in M. xanthus, such as ampicillin, D-cycloserine, and phosphomycin, accelerates the onset of aggregation and sporulation in developing populations of cells. In addi tion, the exogenous induction of beta-lactamase allows M. xanthus to fruit on media containing concentrations of nutrients that are normally too high to support development. We propose that the induction of beta-lactamase is an integral step in the development of M, xanthus and that this induction i s likely to play a role in aggregation and in the restructuring of peptidog lycan which occurs during the differentiation of spores. In support of this hypothesis, we show that exogenous induction of beta-lactamase can rescue aggregation and sporulation of certain mutants. Fruiting body spores from a rescued mutant are indistinguishable from wild-type fruiting body spores w hen examined by transmission electron microscopy, These results show that t he signal transduction pathway leading to the induction of beta-lactamase p lays an important role in aggregation and sporulation in M. xanthus.