Soil fertility impact on recruitment and diversity of the soil microbiome in sub-humid tropical pastures in Northeastern Brazil.

Soil fertility is key point to pastures systems and drives the microbial communities and their functionality. Therefore, an understanding of the interaction between soil fertility and microbial communities can increase our ability to manage pasturelands and maintain their soil functioning and productivity. This study probed the influence of soil fertility on microbial communities in tropical pastures in Brazil. Soil samples, gathered from the top 20 cm of twelve distinct areas with diverse fertility levels, were analyzed via 16S rRNA sequencing. The soils were subsequently classified into two categories, namely high fertility (HF) and low fertility (LF), using the K-Means clustering. The random forest analysis revealed that high fertility (HF) soils had more bacterial diversity, predominantly Proteobacteria, Nitrospira, Chloroflexi, and Bacteroidetes, while Acidobacteria increased in low fertility (LF) soils. High fertility (HF) soils exhibited more complex network interactions and an enrichment of nitrogen-cycling bacterial groups. Additionally, functional annotation based on 16S rRNA varied between clusters. Microbial groups in HF soil demonstrated enhanced functions such as nitrate reduction, aerobic ammonia oxidation, and aromatic compound degradation. In contrast, in the LF soil, the predominant processes were ureolysis, cellulolysis, methanol oxidation, and methanotrophy. Our findings expand our knowledge about how soil fertility drives bacterial communities in pastures.

Metagenome assembled-genomes reveal similar functional profiles of CPR/Patescibacteria phyla in soils.

Soil microbiome is one of the most heterogeneous biological systems. State-of-the-art molecular approaches such as those based on single-amplified genomes (SAGs) and metagenome assembled-genomes (MAGs) are now improving our capacity for disentailing soil microbial-mediated processes. Here, we analysed publicly available datasets of soil microbial genomes and MAG's reconstructed from the Amazon's tropical soil (primary forest and pasture) and active layer of permafrost, aiming to evaluate their genome size. Our results suggest that the Candidate Phyla Radiation (CPR)/Patescibacteria phyla have genomes with an average size fourfold smaller than the mean identified in the RefSoil database, which lacks any representative of this phylum. Also, by analysing the potential metabolism of 888 soil microbial genomes, we show that CPR/Patescibacteria representatives share similar functional profiles, but different from other microbial phyla and are frequently neglected in the soil microbial surveys. Finally, we argue that the use of MAGs may be a better choice over SAGs to expand the soil microbial databases, like RefSoil.