Marine biofilm microbial communities on deep-sea moorings as indicators of a changing environment.

Marine biofilms developed on buoys encasing Acoustic Doppler Current Profilers (ADCPs), deployed on deep-sea moorings for current measurements, were characterized for the first time along the continental slope of the west coast (Off Okha, Goa, Kollam) and east coast (Off Vishakhapatnam - Vizag) of India at a depth of ∼150 m over three years. The biofilm community structure and functions were elucidated using next-generation sequencing. High-throughput sequencing revealed spatio-temporal variations in the biofilm communities with site-specific microbial signatures and metabolic functions. Moreover, biofilms from the Bay of Bengal were significantly different from those in the Arabian Sea. Interestingly, Kollam biofilms were characterized by photoautotrophic carbon cycling and dominated by several cyanobacterial communities and purple non-sulfur bacterium, and is the first report of such taxa in marine biofilms at a depth of 150 m. Functional predictions indicated enhanced expression of stress-related pathways in the Vizag and Goa biofilms. Additionally, biofilms from all sites actively contributed to the degradation of carbon, nitrogen, sulfur, and hydrocarbons, highlighting their importance in marine biogeochemical processes. Notably, certain biofilm-forming genera were consistently present across all 3 years at specific sites, indicating ecological resilience and serving as bioindicators of long-term biofilm dynamics. Moreover, the presence of plastic-associated genera (Amphritea, Crocinitomix, Ulvibacter, and Oleiphilus) across several sites reflects the widespread occurrence of plastics in the surrounding marine environment. Emergence of Desulfobacterota post-lockdown in Okha biofilms suggests anthropogenic influence from increased petroleum activity and their role as markers of hydrocarbon contamination. The detection of sulfur-cycling and corrosion-associated taxa (Sulfurovum, Sedimenticola, Photobacterium, Tenacibaculum) suggests a persistent risk of microbially induced corrosion (MIC), potentially compromising the durability of oceanographic instruments/installations. These findings on deep ocean biofilm-forming bacteria not only provide valuable insights into the ecological and biogeochemical capabilities of microbes but also highlight their relevance as site-specific microbial signatures of marine pollution. This research can also aid in developing effective strategies to mitigate biofouling and bio-corrosion on oceanographic instruments.