Brözel Lab

To build and maintain populations in soil, bacteria must contend with nutrient limitation in a competitive environment. This is different to clonal populations growing in nutrient-rich laboratory media. In soil, rapid growth to high density can only occur in nutrient hot-spots such as organic substrates exuded by growing roots. Yet hot-spots attract diverse taxa, leading to competition among species.

Rapid growing model species such as Escherichia coli, Bacillus subtilis and Pseudomonas fluorescens shaped our bacterial physiology mindset that bacteria grow exponentially to stationary phase, survive for a while and eventually die. The phenomenon rests on provision of organic compounds such as sugars and amino or organic acids, replenished regularly. Outside of nutrient hot-spots, soil does not receive regular input of organic carbon. For species to maintain populations in nutrient limited soil, they must focus on maintenance rather than growth. Thus, soil bacteria likely evolved to preserve resources for long-term population maintenance.

Successful population maintenance under nutrient limiting, competitive conditions should include the development of both co-operative and competitive mechanisms. Networks of cooperating bacteria may contribute specific functions such as hydrolyzing complex carbohydrates or fixing atmospheric nitrogen. Conversely taxa in competition would exert deleterious factors without expending excessive energy.

To address these questions, we study soil bacteria under soil-mimicking conditions, based at South Dakota State University.