SHIFTS IN THE BACTERIAL COMMUNITY STRUCTURE AND DIVERSITY IN BRAZILIAN SOILS AMENDED WITH ELEMENTAL SULFUR

Adriano Reis Lucheta (ESALQ/USP); Marcio Rodrigues Lambais (ESALQ/USP)

Depletion of sulfur levels in soil has been observed as a result of agricultural practices and biomass harvesting. Elemental sulfur (S⁰) may be an interesting fertilizer, however it must be oxidized to sulfate in order to be taken up by plants. Biological oxidation of S⁰ is commonly associated with certain bacterial species, such as Acidithiobacillus thiooxidans, although many studies failed to detect them in soils. Recent efforts have shown a great diversity of bacteria able to oxidize reduced forms of sulfur in soil, besides A. thiooxidans. Nevertheless, no information is available for Brazilian soils. The aim of this work was to determine the bacterial communities associated to S⁰ oxidation in Brazilian soils. The bacterial community structure and diversity in three Brazilian soils amended and not with 10 g of S⁰ kg^-1 was compared by partial sequencing of 16S rDNA, after 102 days incubation under microcosm conditions. Metagenomic DNA was extracted from 0,5g of soil using the Fast DNA kit. Fragments of 16S rDNA were amplified by PCR using primers BAC8F and BAC1541R, cloned into the pGEM-T Easy vector and sequenced. Useful 455bp sequences were compared with sequences in the Ribosomal Database Project II. Operational Taxonomic Units (OTUs) were determined using DOTUR, using 97% of similarity to define species. Diversity (Shannon and Simpson’s Reciprocal) and Richness Indices (Chao and ACE) were calculated using SPADE. Neighbor-joining phylogenetic trees were assembled using Kimura-2 evolutionary distance in Mega, and graphically edited at I-tol website. The predominant phyla in the soils analyzed were Acidobacteria, Actinobacteria, Firmicutes and Proteobacteria. Treatment with S⁰ increased the number of bacterial OTUs assigned to Firmicutes in the sand soil, whereas OTUs assigned to Actinobacteria were more abundant in the clay soil. Proteobacteria and Acidobacteria populations were negatively affected by S⁰ treatment. Phylogenetic affiliation of the OTUs unique to the S⁰ treated soils showed high levels of similarity with Actinobacteria subclass Rubrobacteridae and Firmicutes class Bacillales (B. cereus, Paenibacillus sp. and Alicyclobacillus sp.) and Clostridiales. Our data suggest that Actinobactreria and Bacillales may play a role in S⁰ oxidation in the evaluated soils, whereas OTUs related to A. thiooxidans were not detected. Acknowledgement: FAPESP.