RESUMO
Mangroves are complex land-sea transition ecosystems whose microbiota are essential for their nutrient recycling and conservation. Brazil is the third-largest estuarine area in the world and "Baía de Todos os Santos" (BTS) is one of the largest bays of the country, with wide anthropogenic exploration. Using a metagenomic approach, we investigated composition and functional adaptability as signatures of the microbiome of pristine and anthropized areas of BTS, including those under petroleum refinery influence. The taxonomic analysis showed dominance of sulfate-reducing Desulfobacteraceae, Rhodobacteraceae, and Flavobacteriaceae. Taxa were significantly diverse between pristine and disturbed areas. Disturbed mangroves showed a notary increase in abundance of halophilic, sulfur-related, and hydrocarbon-degrading genera and a decrease in diatoms compared to pristine area. The metabolic profile of BTS mangroves was correlated with the differentially abundant microbiota. Two ecological scenarios were observed: one marked by functions of central metabolism associated with biomass degradation and another by mechanisms of microbial adaptability to pollution conditions and environmental degradation. Part of the microbiome was distinct and not abundant in Brazilian estuarine soils. The microbiome signature observed in each BTS mangrove reflects how human actions impact the diversity of these ecosystems and also emphasize their role in attempting to restore disturbed mangroves. The microbiome may act as a potential biological indicator of the preservation status of these soils, despite the limitation of soil property conditions. Additionally, our data pointed to metagenomics as an additional tool for environmental assessment and reinforced the need for protective measures for the mangroves under study.
RESUMO
Mangroves are ecosystems of economic and ecological importance. Laguncularia racemosa (Combretaceae), popularly known as white mangrove, is a species that greatly contributes to the community structure of neotropical and West African mangrove forests. Despite the significance of these ecosystems, they have been destroyed by oil spills that can cause yellowing of leaves, increased sensitivity to other stresses and death of trees. However, the molecular response of plants to oil stress is poorly known. In this work, Illumina reads were de novo assembled into 46,944 transcripts of L. racemosa roots and leaves, including putative isoform variants. In addition to improving the genomic information available for mangroves, the L. racemosa assembled transcriptome allowed us to identify reference genes to normalize quantitative real-time PCR (qPCR) expression data from oil-stressed mangrove plants, which were used in RNASeq validation. The analysis of expression changes induced by the oil exposure revealed 310 and 286 responsive transcripts of leaves and roots, respectively, mainly up-regulated. Enriched GO categories related to chloroplasts and photosynthesis were found among both leaf and root oil-responsive transcripts, while "response to heat" and "response to hypoxia" were exclusively enriched in leaves and roots, respectively. The comparison of L. racemosa 12-h-oil-stressed leaf expression profile to previous Arabidopsis heat-stress studies and co-expression evidence also pointed to similarities between the heat and oil responses, in which the HSP-coding genes seem to play a key role. A subset of the L. racemosa oil-responsive root genes exhibited similar up-regulation profiles to their Arabidopsis homologs involved in hypoxia responses, including the HRA1 and LBD41 TF-coding genes. Genes linked to the ethylene pathway such as those coding for ERF TFs were also modulated during the L. racemosa root response to oil stress. Taken together, these results show that oil contamination affects photosynthesis, protein metabolism, hypoxia response and the ethylene pathway in L. racemosa 12-h-oil-exposed leaves and roots.
