Database of raw 16s rRNA sequences from an ultra-small bacterial community able to degrade microcystin from Jacarepaguá Lagoon, Rio de Janeiro, Brazil. Ultra-small bacterial community from Jacarepaguá Lagoon, Rio de Janeiro, Brazil

Cyanobacterial blooms affect biotic interactions in aquatic ecosystems, including those in the microbial community, but the complexity of these interactions are still little explored. Besides that, there is a possibility of a chemical compound exchange such as metabolites and/or signaling-molecules produced by them. Among these, the biodegradation of cyanotoxins by some heterotrophic bacteria can be studied for ecological and technological purposes, especially to the cyclic peptide microcystin (MC), due to its widespread occurrence in freshwater. In this study, we investigated MC-biodegradation by bacterial community from a coastal lagoon historically contaminated by this toxin, emphasizing in an ultra-small bacterial community (USBc) activity. Surface water was sampled in different dates from Jacarepaguá lagoon (Rio de Janeiro, Brazil). Microbial communities were recovered by centrifugation and separated according size fractions by filtration (<0.45 μm and <0.22 μm bacteria size). Each fraction was incubated with a natural and relevant concentration of MC-LR (~20 ng.mL-1) for 7 days at 25 ºC. MC-LR concentrations were determined by LC-MS/MS and the toxin was degraded in all cases. The bacterial communities at days 0 and 7 were characterized by 16s rRNA sequencing and transmission electron microscopy. To recognize the MC-LR effect on the community, we evaluated both fractions maintained over 7 days without toxin. Microscopy revealed a few bacteria in each fraction at time 0 and uncommon morphologies into <0.22 μm fraction. In addition, a morphological diversity was observed in each fraction with larger cells and in a higher abundance after 7 days MC-LR-incubation. Sequencing revealed a change in bacterial community composition exposed to MC-LR and led to an enrichment of certain taxa, especially Methylophilales order. The same taxa were present in both size fractions. To our knowledge, this is the first study exploring the biodegradation of MCs by USBc.