A simple culture technique of Rhodobacter azotoformans EBN-7 for public use: application to NH4+-N removal in shrimp aquaculture water

Abstract

Photosynthetic bacteria (PSB) attract considerable interest as useful microorganisms; nevertheless, a generalized culture technique has not been previously reported owing to difficulty in their cultivation. Therefore, a simple culture technique suitable for public use was investigated. Among the PSB tested, the strain Rhodobacter azotoformans EBN-7 was the most suitable for scaleup production because it showed the highest specific growth rate (0.20 h−1) on basal medium. In scale-up cultivation (500 L), R. azotoformans EBN-7 showed 4.50 × 1010 colony-forming units mL−1 (number of viable cells), dry cell weight of 26.8 g/L, and a specific growth rate of 0.15 h−1. Cultivation using this final culture broth (as seed culture) in a 15 L simple reactor was successful, with maintenance of cell activity evident. For use as seed culture, the maximum allowable preservation period of R. azotoformans EBN-7 at 4°C was 3 months. When R. azotoformans EBN-7 cultivated in a simple technique was applied to shrimp aquaculture water, NH4+-N was reduced from 0.61 mg/L to 0.24 mg/L (by 60.7%) in 4 days in comparison with the control. Thus, this simple culture technique using R. azotoformans EBN-7 has the potential for a good removal efficiency of NH4+-N, making seed culture easier and suitable for public use.