RESUMO
L-Lysine is an essential amino acid that is required in the diet of humans and animals. It is utilized in human medicine, cosmetics and pharmaceutical industry. ’The influence of agitation rates, pH and calcium carbonate on L-lysine production by Bacillus subtilis using agricultural products as carbon and nitrogen sources was studied. The L-lysine-producing bacteria had already been isolated from Nigerian soil. They were purified and Identified as B. subtilis PR13 and B. subtilis PR9, using cultural, biochemical and molecular characteristics. Optimization of some parameters which included agitation rates, pH values and CaCO3 concentrations, on L-lysine production by the Bacillus species was carried out. The L-lysine was produced in 250 ml flasks containing fermentation media (FM1 and FM2). The findings revealed that, enhanced L-lysine yield of 2.10 and 1.33 mg/ml was observed at agitation rate of 180 rpm for B. subtilis PR13 and PR9 respectively. There was a positive correlation between agitation rates and L- lysine production by B. subtilis PR13 and PR9 (r = 0.96 and 0.83 respectively). The pH of 7.5, stimulated optimum L- lysine yield of 2.27 mg/ml for PR13 and 1.38 mg/ml for PR9. There was a positive correlation between pH values and L-lysine production by B. subtilis PR13 and PR 9 (r = 0.63 and 0.50 respectively). The supplementation of 40g/l of CaCO3, enhanced optimum L-lysine yield of 2.18 mg/ml for B. subtilis PR 13 and 1.30 mg/ml for B. subtilis PR9. There was a positive correlation between varying concentrations of calcium carbonate and L-lysine production by the B. subtilis PR13 (r =0.35), while negative correlation was observed for B. subtilis PR 9 (r = -0.10). The results obtained in the study illustrated that the optimization of process parameters could increase the L-lysine yield from agricultural products by B. subtilis PR13 and B. subtilis PR9.
RESUMO
Proteases are one of the most industrially important enzymes, which account for about 60% of total enzyme market. Protease production by submerged fermentation in shake flasks using Bacillus sp. isolated from the soil was studied. Soil samples were collected from different locations within Chukwuemeka Odumegwu Ojukwu University, Uli, Anambra state. The soil samples were serially diluted and inoculated on sterilized skim milk agar plates. The plates were incubated at 30oC for 72 h. A clear zone around the colonies gave an indication of protease-producing bacteria isolates. The selected protease producers were subsequently used for shake flask fermentation in 50 ml sterile medium. Optimization study was conducted to determine the effect of carbon sources, nitrogen sources, trace elements, agitation rates and pH. Twenty one bacteria isolates were found to be active protease producers and isolates RS-5 and OS-9 had the highest zone of clearance of 13.5 and 12.1 mm respectively. The result of submerged production of protease by the bacteria isolates revealed that the isolates RS-5 and OS-9 accumulated maximum protease yield of 3.23 and 2.71 U/ml respectively. The isolates were Gram positive and endospore formers, and were identified as Bacillus sp. RS-5 and OS-9.The addition of Starch and maltose stimulated optimum protease production of 3.47 and 2.77 U/ml by Bacillus sp. RS-5 and OS-9 respectively. Beef extract enhanced maximum enzyme yield of 3.35 and 2.90 U/ml for Bacillus sp. RS-5 and OS-9 respectively. Maximum protease yield of 3.28 U/ml for Bacillus sp. RS-5 and 2.85 U/ml for Bacillus sp. OS-9 was obtained by the supplementation of 0.4 g/l of FeS04 respectively. The maximum protease yield was observed at agitation rate of 200 rpm for Bacillus sp. RS-5 and 170 rpm for Bacillus sp. OS-9. At pH8, protease accumulation was highest for Bacillus sp. RS-5 and OS-9. The study revealed that the soil harbours some protease-producing bacteria strains and protease production can be greatly enhanced through optimization of process parameters.