Factors affecting the response of marine and estuarine bacterial communities to trace metal enrichment
Studies of the effects of trace metal perturbation on microbial communities have, to date, concentrated on contaminated environments, single phylotypes or single metals. The effects of trace metals on bacterial communities in estuarine and marine environments have been largely overlooked. The aim of this research was to advance the scientific knowledge in this area by the implementation of incubation experiments. Experiments were designed to determine the effects of trace metal enrichment and aggregate formation on the structure and function of bacterial communities. Environmental samples included bacterioplankton from a pristine estuary (Erme, Devon), a moderately contaminated estuary (Tamar, Devon), a contaminated estuary (Fal, Cornwall), a coastal station (M1) and a truly marine station off the continental shelf (M2). Key factors influencing the response of bacterial communities to trace metal enrichment were identified. In marine communities the most influential factors were; environmental parameters, such as type and concentration of organic matter; initial community composition and ambient concentration of zinc. The addition of trace metals resulted in a decrease in diversity in the bacterial community from the Tamar Estuary, however, bacterial association with aggregates appeared to reduce this effect. Community dynamics of bacteria from a pristine estuary (Erme) demonstrated remarkable bacterial resilience under trace metal stress, particularly in samples dominated by bacteria from the Rhodobacteraceae. Some metals were shown to have a more profound effect on community dynamics than others, resulting in the division of trace metals into Type 1 and Type 2 categories as a function of bacterial response. RNA derived community fingerprints were more different between incubation conditions than DNA derived fingerprints, and were thus a more sensitive indication of response to trace metal enrichment. The wider implications of the effects of trace metals on bacterial communities in estuarine and marine environments are discussed, along with possible future research directions. Recommendations are made for future investigations of the effects of metal contamination in light of the results presented here.