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While environmental drivers regulate the structure of mangrove microbial communities, their exact nature and the extent of their influence require further elucidation. By means of 16S rRNA gene-based sequencing, we determined the microbial taxonomic profiles of mangroves in the subtropical Paranaguá Bay, Brazil, considering as potential drivers: salinity, as represented by two sectors in the extremes of a salinity gradient (<5 PSU and >30 PSU); proximity to/absence of the prevailing plants, Avicennia schaueriana, Laguncularia racemosa, Rhizophora mangle, and Spartina alterniflora ; and the chemical composition of the sediments. Salinity levels within the estuary had the strongest influence on microbial structure, and pH was important to separate two communities within the high salinity environment. About one fourth of the total variation in community structure resulted from covariation of salinity and the overall chemical composition, which might indicate that the chemical profile was also related to salinity. The most prevalent bacterial phyla associated with the mangrove soils analyzed included Proteobacteria , Actinobacteria , Chloroflexi , Bacteroidetes , Acidobacteria, and Cyanobacteria. Taxonomic and functional comparisons of our results for whole-genome sequencing with available data from other biomes showed that the studied microbiomes cluster first according to biome type, then to matrix type and salinity status. Metabolic functions were more conserved than organisms within mangroves and across all biomes, indicating that core functions are preserved in any of the given conditions regardless of the specific organisms harboring them. Unlabelled Image • Metataxonomics revealed three microbial communities in subtropical bay mangroves. • Microbiota structure was mainly driven by salinity and pH gradients. • Metagenomics showed that microbiota and functions from saline sediments are similar. • Salinity also has a role in discriminating microbiomes from a more diverse nature. • Functions are more conserved than microorganisms across different biomes. [ABSTRACT FROM AUTHOR]

Abstract The Pampa biome is a rich and fertile area of grassland in Brazil, South America, which has been considered ecologically important owing to its enriched biodiversity. However, this landscape has undergone serious fragmentation, with half of its original vegetation being removed due to continuous agricultural activities and its widespread use for livestock production. The excessive cattle farming has generated a significant grazing load on the area, which is reflected in the diminishing soil microbial diversity. With an aim to study the impact of increasing grazing load on microbial diversity of soil of pampas, the present study compared the bacterial communities of grassland-controlled soils of the Pampa biome under different grazing pressures: high (HG), moderate (MG), low (LG), and a control area (CG) in a long-term experiment using high-throughput sequencing. The soil microbial community was not significantly affected by the presence or absence of bacterial taxonomic groups; however, significant changes were detected in each different grazing pasture sample. This observation was especially notable in MG pressure that, when compared to other grazing pressures and control grazing (CG), was found to be associated with an increased prevalence of some specific groups of microorganisms. These include those belonging to the following families: Nitrospirae , DA052, Syntrophobacteraceae , Methylocystaceae , Syntrophaceae , Mycobacteriaceae , and Koribacteraceae. Moreover, the grazing pressure disturbance created by MG was believed to enhance the diversity of a bacterial community, thereby maintaining the stability of soil and indicating that stressed bio-systems might be more stable than those not experiencing stress. Thus, the results of the current study imply that quantitative and qualitative changes in the composition of the soil bacterial community could serve as an important indicator of both short- and long-term changes in soil health. Graphical abstract Unlabelled Image Highlights • Effect of different grazing pressures loads on the soil bacterial community assessed. • Statistically significant changes were observed in different grazing pastures samples. • Moderate grazing pressure differed in relation to the other grazing pressures. • Moderate grazing pressure disturbance adds diversity to a bacterial community - Intermediate Disturbance Hypothesis. [ABSTRACT FROM AUTHOR]