Diversity and Novel Strains of Sulfur Compounds Degrading Bacteria in the Swinery Sludge

Abstract

A study on the diversity and novel strains of sulfur compounds degrading bacteria was performed as the ultimate aim for the removal of harmful sulfur compounds from a swinery in Jeju. Sulfur-oxidizing bacteria were isolated using sulfur-oxidizing bacteria (SOB) medium from swinery sludge, and bacterial distribution was studied by phylogenetic analysis of the partial 16S rRNA gene. The soxB genes essential for sulfur-oxidizing were successfully amplified from some of the isolates and characterized. The characteristics of thiosulfate oxidation were investigated. As results, the distribution of bacterial populations in the sludge collected from 5 swineries was analyzed by 16S rRNA gene sequence analysis. A total of 351 strains of sulfur-oxidizing bacteria were isolated through the enrichment culture from swinery sludge and classified into 6 groups of phyla/class Alpha-, Beta-, Gamma-proteobacteria, Actinobacteria, Bacteriodetes and Firmicute. They were tentatively placed into 16 orders or suborders, 23 families and 48 genera by 16S rRNA sequence analysis. The sulfur oxidizers of the Proteobacteria cluster, Comamonas, Paracoccus and Pseudomonas in the swinery sludge were the evolutionary cousins of widespread swinery sludge bacteria of the same group. The soxB genes were found in 13 strains, which reveal the presence of sulfur-oxidizing bacteria in the swinery sludge. Among these were 16S rRNA sequences, 7 genera, including Acinetobacter, Alicycliphilus, Comamonas, Hydrogenophaga, Paracoccus, Pseudomonas and Rhodobacter, represented the new sulfur oxidizers in swinery sludge. Phylogeny based on the amino acids sequences of soxB gene was created using 9 strains of Beta-proteobacteria and 4 strains of Alpha-proteobacteia. The BLAST search showed the thiosulfate-oxidizing bacteria isolated from swine sludge fell into four different genera, Comamonas, Methylibium, Paracoccus and Thiobacillus with 80-81 % sequence similarities. The sulfate assay using a modified standard turbidimetric method revealed that strains BB11 and BB12 produced the highest amount of sulfate accumulation 175.5 and 128.2 μg/mL, respectively. Among the isolated strains, 5 strains were considered as candidates for novel genera or novel species according to combined genotypic and phenotypic characterization. Based on the differential phenotypic and chemotaxonomic properties, together with their phylogenetic and genetic distinctiveness, strain KBB12T was considered to be a novel genus and species of the family Comamonadaceae, for which the name Thiobacterium jejuense gen. nov., sp. nov. is proposed, and strain BA15T was also considered a novel genus and species of the family Rhodobacteraceae, for which the name Caenirhodobacter jejuensis gen. nov. was proposed. Strains KBB4T and KBB8T should be considered novel species in the genus Comamonas, for which the name Comamonas jejuensis sp. nov. and Comamonas caeni were proposed, and strain KBB11T should be considered novel species in the genus Hydrogenophaga, for which the name Hydrogenophaga thiooxydans sp. nov. was proposed. The results of this study could be used as the basic data for current issues in the livestock industry, especially in excrement treatment in Jeju. Since SOB reduce pollutants in livestock manure, they could be used in swineries to clean and improve the environment quality in Jeju. Future studies should focus on the isolation of such powerful SOB from swinery sludge or other sources. The study aimed to characterize the metabolism of sulfur by SOB to sulfide or other inorganic reduced forms of sulfur and determine the role of these bacteria on the degradation of sulfur compounds for the improving environmental conditions.