Shiro Nagai

Use of photosynthetic bacteria for the production of SCP and chemicals from organic wastes

Photosynthetic bacteria are anoxygenic phototrophs distributed widely in nature in such habitats as fields, lakes, ponds, rivers and oceans. Bacteria have the capability to utilize sulfate, thiosulfate and hydrogen as electron donors as well as various organic compounds, and are able to fix carbon dioxide and molecular nitrogen under anaerobic-light conditions (Pfenning, 1978; Hoshino and Kitamura, 1984; Truper and Pfenning, 1989; Sasaki et a1., 1995a). Hence, the bacteria play an important role in the circulation of sulfur and nitrogen in the acquatic environment (Kobayashi, 1984).

SCP Production by Mixed Culture of Rhodocyclus gelatinosus and Rhodobacter sphaeroides from Cassava Waste

Abstract The amylolytic enzymes produced by Rhodocyclus gelatinosus hydrolyzed cassava starch mainly to maltose and a small amount of glucose. The organism utilized maltose at the specific growth rate of 0.15 l/h, but in the presence of glucose, maltose consumption rate was retarded. Therefore, a series of mixed cultures was conducted with Rhodobacter sphaeroides P47, which showed a high growth rate of 0.2 l/h on glucose and contained 29.5 μg/g cell of vitamin B12 and 0.49 mg/g cell of carotenoid compared with the 18.4 μg/g cell and 0.23 mg/g cell respectively of Rc. gelatinosus. Mixed cultures with three different inoculum ratios of the two organisms based on cell number all gave higher growth yields and contents of vitamin B12 and carotenoid in the total cell mass than single cultures. When the inoculum ration of Rc. gelatinosus to Rb. sphaeroides P47 was over 1.0, the culture time was shortened due to the synergistic effect of sugar consumption. Therefore, it was suggested that the mixed culture of these two organisms would be practically profitable for more nutritive SCP production from cassava waste.

SCP production of Rhodopseudomonas sphaeroides on pineapple wastes

Abstract Rhodopseudomonas sphaeroides P47, a purple non-sulfur photosynthetic bacterium was isolated from fresh water in the Bangkok area. The organism was selected for SCP production from Pineapple peep waste (total sugar about 100 g/l) based on its high growth rate (0.3 l/h), the capability of reduing high COD waste from 110.3 to 16.3 g/l, i.e. 85.3% COD reduction, and the usefulness for feed supplement due to the high contents of vitamin B12 (75 μg/g cell) and photopigments (carotenoid, 0.8; chlorophyll, 3.2 mg/g cell). The pineapple waste solutiong (1 l) mainly contained 40.1 g sucrose, 23.6 g glucose, and 14.0 g fructose. A medium was prepared by the addition of (NH4)2HPO4, 3 g; (NH4)2 SO4, 13 g; nicotinic acid, 4 mg; thiamine-HCl, 8 mg; and biotin, 0.06 mg per liter waste solution. During the cultivation under aerobic, dark conditions (37°C, pH 7), glucose and fructose were preferentially consumed during the inductive state of sucrose consumption, which was completely used up to the end of cultivation (60 h). The cell mass produced was 26.5 g dry cell/l from 100 g total sugar/l indicating that a growth yield from total sugar of 0.45 g cell/g sugar consumed. R. sphaeroides P47 might be useful for SCP production from pineapple waste since 2.5 tons dry cell/day would be recovered from 150 tons of peel waste/day discharging from a medium sized pineapple cannery in Thailand.