Sentinel bacteria identification on mangrove sediments polluted with heavy metals in the Northwest Coast of South America.

Mangrove ecosystems have been exposed to heavy metals for several decades, a disturbance that affect negatively the biota inhabiting this highly productive environment. However, bacterial members inhabiting this disturbed mangrove sediments have shown the ability to adapt and proliferate in these harsh environmental conditions. Mangroves in the Northwest Coast of South America have been heavily impacted by untreated wastewater discharges from several industries that surrounded pristine and unevaluable mangrove ecosystems. Heavy metals levels (Ag, Cd. Co, Cu, Mn, Mo, Ni, Pb, Se, Sn and Zn) and analysis of the V4 region of the 16S rRNA gene of both polluted and pristine mangrove reveal marked differences in the metal concentration and bacterial composition between them.Core mangrove sediments bacteria include 8,648 OTUs, mostly associated to Proteobacteria, Firmicutes, and Bacteroidetes phyla. At lower taxonomic levels, as class (i.e. Deltaproteobacteria, Anaerolineae) and genera (i.e. Clostridiisalibacter), there are marked differences between the sites analyzed. However, several specific OTUs were associated to either elevated concentrations of heavy metals, such as Desulfobacteraceae (Proteobacteria) and Anaaerolineacea (Chloroflexi), or low heavy metal concentration, such as Clostridiisalibacter sp. (Clostridia), Rhodobacteraceae (Proteobacteria) and Bacillaceae (Firmicutes). This positive correlation between metal concentration and abundance of these OTUs, make these bacterial taxa good sentinel candidates for ecological restoration programs on contaminated mangrove sediments.Keywords: sentinel bacteria, mangrove sediments, heavy metals pollution, environmental monitoring, 16S rRNA gene high throughput sequencing