Successional Changes in Bacterial Assemblage Structure during Epilithic Biofilm Development

Abstract

Although bacteria are often treated as one entity in ecological studies, bacterial assemblages are composed of individual species populations. Bacterial assemblages can have their own richness and structure, analogous to communities of plants and animals, although few studies have attempted to describe spatial or temporal patterns in their structure. In this study, we examined successional changes in the structure of bacterial assemblages using denaturing gradient gel electrophoresis (DGGE) analysis of polymerase chain reaction amplified 16S rDNA fragments. Bacterial biofilm assemblages developing on glass slides in a mesocosm and a small lake showed an initial increase in richness over the first week, followed by a slight decrease and a subsequent increase after two to three months. Functional changes in the bacterial community were examined using most probable number estimates and revealed decreases in the abundance of glucose- and cellulose-degraders during biofilm development, whereas benzoate-degraders became more abundant in the lake biofilms. The banding patterns observed on DGGE gels were used to derive rank-abundance profiles for each stage of biofilm development. These profiles resembled those observed for communities of macroorganisms and could usually be described by geometric series models. These models suggested greater equitability in bacterial community structure as the biofilms developed. A comparison of two successional series of biofilms separated by 30 d revealed that neither successional stage nor time of sampling was the major factor influencing bacterial assemblage structure. Our results allowed us to suggest a general model for the development of bacterial biofilm assemblages that emphasizes the interaction of species and resource diversity. This model suggests that, at least in biofilms, bacterial assemblages may not be structured by the resource competition or niche-driven patterns typical of communities of macroorganisms.