Microbial indicators and Quality Ratio index for risk assessment in oil contaminated sediments of tropical coast
Résumé
Due to anthropogenic activities, coastal sediments are prone to hydrocarbon contamination,
which can be reflected in the microbial community structure and diversity. In order to determine
the impact of oil contamination on the microbial assemblages inhabiting the sediment of several
stations located around the Sepetiba Bay (Brazil), highly impacted by human activities, several
approaches were combined. Chemical contamination factor (CF, n-alkanes [CFn-alkanes] and
16PAHs [CF16PAHs]) and Quality Ratio (QR) index for ecological risk assessment were combined
with microbial community characterization (16S rRNA gene sequencing). Oil pollution (CFn-alkanes
and CF16PAHs) present a general decreasing trend from the internal to the external sector. The
QR, a function of the microbial term (dehydrogenase/esterase enzymatic activities) and the
geochemical term (TOC × CF16PAHs/fine-grained content), ranked most of the internal sector
stations as moderate and high risk to the local biota. The canonical correspondence analysis,
explaining 55% of the microbial community composition variation (ASV level), exhibited the
CF16PAHs as the main factor driving the microbial community structure. Phylogenetic analysis
revealed predominance of Proteobacteria (54%) phylum with a high abundance of the gammadelta-
and alpha-proteobacterial classes (29%, 21%, and 3% respectively), among which diverse
members have been described as capable of degrading hydrocarbons. Among the potential
hydrocarbon-degrading bacterial taxa, the most prevalent genera were Vibrio (12%),
Desulfatiglans (11%), and Bacillus (8%). The cluster correlation analysis revealed prokaryotic
taxa resistant in the internal sector, which mainly present anaerobic metabolisms linked to
sulfate-reduction, methanogenesis, and hydrocarbon-degradation. The Linear discriminant
analysis effect size revealed habitat-specific bioindicators according to the QR risk classification:
(a) JTB255 marine benthic group (low risk); (b) Bacillus (moderate risk); and (c) sulfatereduction
bacteria (high risk). Overall, the microbiota structure validated the QR risk
classification, revealing both useful and efficient for monitoring the sediment quality status and
risk of coastal sediments.