Efficacy of amorphous TiOx-coated surfaces against micro- and macrofouling through laboratory microcosms and field studies.

In this study, Soda Lime Glass (SLG) and Stainless Steel (SS316L) substrata coated with Titanium oxide (TiOx) were tested for their efficacy in the laboratory microcosms and in field against micro- and macrofouling. Laboratory microcosm studies were conducted for five days using natural biofilms, single-species diatom (Navicula sp.), and bacterial biofilms, whereas field observations were conducted for 30 days. The TiOx-coating induced change in the mean contact angle of the substratum and rendered SS316L more hydrophilic and SLG hydrophobic, which influenced the Navicula sp. biofilm, and bacterial community structure of the biofilm. Overall, the TiOx-coated SS316L showed minimal microfouling, whereas non-coated SLG exhibited greater efficacy in deterring/preventing macrofouling organisms. Moreover, the reduction in macrofouling could be attributed to high abundance of Actinobacteria. Unraveling the mechanism of action needs future studies emphasizing biochemical processes and pathways.

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.

Influence of Darkness and Aging on Marine and Freshwater Biofilm Microbial Communities Using Microcosm Experiments.

Ballast tank biofilms pose an additional risk of microbial invasion if sloughed off during ballasting operations, yet their significance and invasion biology is poorly understood. In this study, biofilms developed in marine and freshwater locations were exposed to prolonged darkness and aging by mimicking ballast water conditions in the laboratory. Upon prolonged darkness, the decay of phytoplankton, as indicated by the decrease in chlorophyll a in marine biofilms, led to remineralization and enhanced bacterial and protist populations. However, the same trend was not observed in the case of freshwater biofilms wherein the microbial parameters (i.e., bacteria, protists) and chlorophyll a decreased drastically. The bacterial community structure in such conditions was evaluated by real-time quantitative PCR (qPCR), and results showed that the biofilm bacterial communities changed significantly over a period of time. α-Proteobacteria was the most stable taxonomic group in the marine biofilms under dark conditions. However, ß-proteobacteria dominated the freshwater biofilms and seemed to play an important role in organic matter remineralization. γ-Proteobacteria, which includes most of the pathogenic genera, were affected significantly and decreased in both the types of biofilms. This study revealed that marine biofilm communities were able to adapt better to the dark conditions while freshwater biofilm communities collapsed. Adaptation of tolerant bacterial communities, regeneration of nutrients via cell lysis, and presence of grazers appeared to be key factors for survival upon prolonged darkness. However, the fate of biofilm communities upon discharge in the new environment and their invasion potential is an important topic for future investigation.