Microbiomes and potential metabolic pathways of pristine and anthropized Brazilian mangroves

Although microorganisms play key roles in mangrove food webs, the global knowledge of their diversity and function in these ecosystems is still scarce. Therefore, this study aimed to describe the microbiomes of pristine (TIM) and anthropized (JAG, PAC and COC) mangroves from a semiarid region of Brazil, and also to compare microbiomes from Southeast (SE) and Northeast (NE) mangroves, aiming to detect patterns related to geographic location. Pyrosequencing of four metagenomes showed that 90% of total classified sequences were assigned to Bacteria with a greater abundance of Proteobacteria (53%-60%), Bacteroidetes (7%-10%), Actinobacteria, Chloroflexi, Firmicutes and Planctomycetes (4%-7%), followed by Acidobacteria, Cyanobacteria and Verrucomicrobia (1.5%-4%) and phyla with relative abundances under 1%. The dominant proteobacterial classes were Deltaproteobacteria, Alphaproteobacteria and Gammaproteobacteria in the pristine (TIM) and in the less anthropized mangroves (JAG and PAC). Interestingly, in COC it was observed a decrease in Gammaproteobacteria with an increase in Betaproteobacteria, possibly related to its eutrophic condition. Our datasets also revealed some previously non-detected phyla in mangroves, comprising rare groups and several candidate divisions, which were previously reported for harsh environments, suggesting the involvement of these groups with the resilience of mangroves in semiarid regions. Comparative in silico analysis of SE and NE microbiomes showed similarities, but it was possible to detect a homogeneous group formed by Northeast mangroves (TIM, JAG and PAC), whereas the eutrophic mangrove (COC) clustered together to the urbanized Southeast mangrove. These results suggest that the semiarid climate might select peculiar bacterial communities and highlight the risk of microbial diversity homogenization due to anthropic actions on mangroves. Despite the detected changes in microbial composition, in general the potential metabolic pathways from these mangroves did not significantly differ. The observed functional redundancy explains the known resilience of these environments.