Screening of urease production by Aspergillus niger strains

In this study, urease production was investigated among thirteen strains of Aspergillus niger; seven strains isolated from soils of Semnan province in Iran and six strains obtained from Persian Type Culture Collection [PTCC]. The enzyme production was screened in two submerged media quantitatively. The registered PTCC 5011 and the native S31 strains showed more urease production than the other eleven strains. The maximum enzyme productions by PTCC 5011 and S31 strains were 106 and 109 U.g-1dry mass in submerged culture, respectively. Also, we used two solid media for screening all of the strains for urease production semi quantitatively. Due to the acceptable correlations between the two methods, the latter can be used as an ancillary method to mass screening of urease production by filamentous fungi

Comparison of lactic acid isomers produced by fungal and bacterial strains

Many organisms produce lactic acid by fermentation, but most industrially important strains are from the genus Lactobacillus and Rhizopus oryzae. L[+]-Lactic acid is the only optical isomer for use in pharmaceutical and food industries because human body is only adapted to assimilate this form. In this research, six strains of Lactobacillus and four strains of R. oryzae [known as high producer] were examined for optical isomers of lactic acid. The production of lactic acid was improved and lactic acid produced in submerged media on rotary shaker incubator. The optical isomers of lactic acid were examined by L[+] and D[-] lactate dehydrogenase kit. All the R. oryzae strains tested produced only L[+] isomer of lactic acid. The highest fungal and bacterial producer strains were R. oryzae PTCC 5263, Lactobacillus plantarum PTCC 1058, L. Bulgaricus PTCC 1332 and L. delbruekii subsp delbruekii PTCC 1333. Lactobacilli strains produced combination of both optical isomers of lactic acid. Among them, L. casei subsp. Casei produced the low amount of D[-]-lactic acid [2%]. The optimum concentration of glucose for lactic acid production by R. oryzae and Lactobacillus strains were 180 g/l and 80-120 g/l, respectively