Bacterial diversity studied by next-generation sequencing in a mature phototrophic Navicula sp-based biofilm promoted into a shrimp culture system

The bacterial diversity of a phototrophic biofilm used as nutrient-recycler into a shrimp aquaculture system and as direct food-source for shrimp was studied by next-generation sequencing, considering the 16S rDNA and metagenomics sequence classification using exact alignments. Biofilm was promoted by the modification of cabon:nitrogen ratio and by the addition of the diatom Navicula sp. as promoter. Results revealed a wide diversity of bacteria thriving into the biofilm; most of the bacteria detected in the biofilm belonged to the Proteobacteria (47%), Chlamydiae/Verrucomicrobia (11%), Bacteriodetes (8%), Planctomycetes (5%) Phylum. Species involved in the decomposition of organic matter, nitrogenous- and sulfurous metabolites were detected; moreover, filamentous species known as biomass-bulking enhancers and producers of adhesin-like compounds were also detected. Surprising results were also obtained by detecting both, strictly anaerobic and aerobic bacteria involved into the metabolism of nitrogenous compounds. Other species not belonging to the marine environment were also detected, but their role is unclear. Finally, the detection of most of these species may constitute a first case report for a phototrophic biofilm. The results suggest an important role of bacteria in this type of biofilm and a complex microbial-interaction network.