Kocuria Rosea HN01: A Newly Discovered Alkaliphilic Humic-Reducing Bacteria Isolated from Cassava Dregs Composting

The aims were to isolate a humus-reducing microorganism from cassava dregs composting and to investigate the main factors affecting humus reduction rate by the isolate. A halotolerant and alkaliphilic humic-reducing strain, designated as HN01, was successfully isolated. The strain was facultatively anaerobic, Gram-positive, coccus-shaped, and identified as Kocuria rosea with 16S rRNA analysis. Microbial growth was observed at NaCl concentrations below 12% (w/v), pHs of 6–10, and temperatures of 15–30°C under aerobic condition. HN01 was capable of anaerobic reducing humic substance analogs, anthraquinone-2,6-benzene sulfonic acid (AQDS), with glucose, sucrose, methanol, ethanol, or glycerol as an electron donor, and the reduction rates were 46, 42, 40, 41, and 37%, respectively, within 48 h at pH 8.5. Organic substrates such as formate, acetate, propionate, and citrate were not available electron donors with respect to AQDS reduction. The range of pHs and NaCl concentrations for humus reduction by strain HN01 were pH 7–10 and NaCl% (w/v) 1–10%; pH 8.5 and 3% NaCl were the optimum.