Interactions between proteolytic and non-proteolytic Pseudomonas fluorescens affect protein degradation in a model community

The metabolic interactions between proteinase-producing bacteria and other members of bacterial communities are poorly investigated, although they are important for the understanding of structure-function relationships in com plex ecosystems. We constructed simple model communities consisting of prot eolytic and non-proteolytic Pseudomonas fluorescens strains to identify rel evant interactions and to assess their specific significance during the mob ilization of protein for growth. The proteolytic or non-proteolytic model c ommunities were established by co-inoculating proteolytic or proteinase-def icient Tn5-mutants of P. fluorescens strain ON2 with the non-proteolytic re porter strain DF57-N3 that expresses bioluminescence in response to nitroge n limitation. The growth medium was composed such that growth would be nitr ogen limited in the absence of proteolytic activity. In the proteolytic com munities data on growth and nitrogen availability showed that the protein h ydrolysates were available to both the proteolytic and the non-proteolytic strain. Competition between these strains profoundly affected both growth a nd proteinase production. Hence, the mobilization of protein was closely co upled to the competitive success of the proteolytic strain. These findings provide new insight into the metabolic interactions that occur when protein is degraded in mixed bacterial communities. (C) 2000 Federation of Europea n Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.