Testing the efficiency of a bacterial community-based index (microgAMBI) to assess distinct impact sources in six locations around the world

MicrogAMBI is a bacterial community-based index, recently developed to assess the ecological status of marine systems. The easy access to High Throughput Sequencing (HTS) technologies, allowing microgAMBI the quick taxonomic identification of bacterial assemblages, providing an early warning signal to assess impacts. MicrogAMBI was developed, applied to human pressures (organic and metal pollution), and validated, in estuaries and coasts of the Basque Country (northern Spain). Here, to test the efficiency of the index, six case studies have been selected, including different substrata and environments (sediment, water column, coral, and a sludge reactor), from polar to temperate and tropical locations. The pressures include a polluted sludge reactor, underground discharges, diffuse pollution, sedimentation, sewage outfalls and eutrophication, as well as two pristine areas, in some cases with spatial and temporal gradients. To calculate the index, the new taxa list includes 693 taxa. The list, being public, will allow to achieve a consensus in the assignation of taxa to ecological groups. This would facilitate the assessment of multiple human pressures, based upon bacteria composition. The study has demonstrated that microgAMBI has the potential to work reasonably well under very different environments and pressures. The index provides a single, clear and efficient way to establish the ecological status, based upon bacteria community composition, along spatial and temporal pressure gradients.