Assesing different diversity metrics to express Archaeal and Bacterial assemblage structure

Abstract

Molecular methods developed over the last years have given a boost to the study of prokaryotic diversity. Both Archaeal and Bacterial assemblages were taken into consideration in the present study, in order to investigate diversity patterns within same habitat and among different environments. Data were provided from previous studies of fresh water, thermal springs and mud volcano environments. A number of 26 metrics including diversity, evenness, and dominance indices were assessed in order to select the most efficient to express microbial assemblage structure. Relative Abundance Distributions (RADs) were additionally employed to explore the structure and diversity of different assemblages. Overall, Bacterial diversity was higher than Archaeal diversity with respect to species richness, diversity, and evenness. This trend was best reflected by the Brillouin diversity, the Evenness E2, and the McNaughton dominance indices. This trend was visualized using RADs, which clearly showed that Bacterial assemblages presented more smooth and “speciose” species-abundance curves, compared to Archaeal assemblages that were characterized by steep, species-poor distributions. Moreover, marked differences were observed for Bacteria among contrasting environments. Although Archaea did not present significant differences among different environments, their diversity was higher in thermal springs, where Bacterial diversity was found to be significantly lower. It is hypothesized that those differences are due to the more efficient and flexible way Bacteria exploit available energy for growth, whereas the increased Archaeal diversity of thermal springs could be due to their capacity to survive under chronic stress.