Influence of sustainability and immigration in assembling bacterial populations of known size and function.

The rational assembly of microbial communities to perform desired functions would be of great practical benefit to society. Broadly speaking, there are two major theoretical foundations for microbial community assembly: one based on island biogeography theory and another based on niche theory. In this study, we compared a parameter from each theory (immigration rate and sustainability, respectively) to ascertain which was more influential in establishing a functional bacterial population in phenol degrading activated sludge over a 30-day period. Two bacterial strains originally isolated from activated sludge, but differing in their ability to sustain a population in this environment, were repeatedly added to activated sludge reactors at different doses. The resulting size of each population was monitored by competitive polymerase chain reaction. Large, unexpected, yet reproducible fluctuations in population sizes were observed. Irrespective of this, difference in the ability to sustain a population in this environment, overshadowed the influence of 100-fold differences in immigration rate.