Microbial Community Activity:Communication Among Soil Microbes

In natural environments, bacteria live in communities of multiple species. In addition to signaling other members of the same species e.g. quorum sensing, other forms of interspecies communication are important for the survival of members of these polymicrobial communities. Preliminary experiments have demonstrated a diffusible signal from Pedobacter which induces P. fluorescens to produce an antifungal substance. Genes in P. fluorescens up-regulated in response to the Pedobacter diffusible signal are being examined for their importance in the interaction. Deletion of two such genes eliminated fungal inhibition. In addition to diffusible signal-mediated interaction, we have discovered a contact-dependent interaction between Pedobacter and P. fluorescens which triggers swarming motility on a 2% agar culture medium. In a soil environment, increased motility may enhance survival by facilitating movement into new niches. We are currently screening transposon mutants of Pedobacter for loss of induction of swarming so as to identify the genes involved. Our completed draft of the Pedobacter genome sequence will enhance analysis of the Pedobacter mutants. In addition, we are studying the P. fluorescens transcriptome while in contact with Pedobacter to decipher the response on a genome-wide level. These data will be compared with microarray results of the P. fluorescens response to the Pedobacter diffusible signal, allowing determination of specific responses to the different signaling mechanisms. With these studies we aim to shed light on the molecular basis by which two different kinds of bacteria communicate with each other, resulting in behaviors which may contribute to fitness in soils.