Ecological Impacts of Aged Freshwater Biofilms on Estuarine Microbial Communities Elucidated Through Microcosm Experiments: A Microbial Invasion Perspective

Inadvertent introductions of alien species via biofilms as a vector released through ballast water are of environmental importance, yet their consequences are not much known. In the present study, biofilm communities developed in an inland freshwater port under in situ and dark conditions were subjected to long-term dark incubations. Subsequently, the impact of these aged biofilms as vectors on estuarine water column communities were evaluated using microcosm experiments in the laboratory. Variations in biofilm and planktonic microbial communities were quantified using quantitative PCR.Upon prolonged dark incubation, a shift in bacterial diversity with an increase in tolerant bacterial communities better adapted to stress was observed. Actinobacteria were the dominant taxa in both aged biofilms upon dark incubations. The laboratory studies indicated that on exposure of these biofilms to estuarine water, resuscitation of Vibrio alginolyticus, V. parahaemolyticus, and V. cholerae from a dormant state existing in these biofilms to culturable form was observed. Moreover, the results revealed that both the biofilm types can pose a threat to the environment, but the degree of risk can be attributed to the imbalance caused by significant changes in the surrounding estuarine microbial communities. Consequently, this may result in either proliferation or decline of some genera with different metabolic potential and resuscitation of pathogenic forms not present earlier, thereby influencing the ecology of the environment. Quantifying these effects in the field using biofilm metagenomes with an emphasis on virulent species and understanding traits that enable them to adapt to changing environments is a way forward.