Mehmet Sait Ekinci

Expression of fungal cellulase gene in Lactococcus lactis to construct novel recombinant silage inoculants.

The facultative anaerobic bacterium Lactococcus lactis has been used as a host for expression of a gene isolated from the anaerobic rumen fungus Neocallimastix sp. The coding region of the cellulase gene was obtained from the fungus with the aid of polymerase chain reaction amplification. The gene was then transformed into pCT vector system and the constructed recombinant plasmid was introduced into two L. lactis strains (IL403 and MG1363) by electroporation. The gene encoding the fungal originated cellulase was expressed in both strains successfully although the expression level was relatively lower in comparison with the original enzyme activity. Genetically modified L. lactis strains were used as silage inoculants for pre-biodegradation of the plant biomass during ensiling. That treatment resulted in a notable reduction of the acid detergent fiber (ADF) and neutral detergent fiber (NDF) contents of the plant biomass used as silage material. Inoculation with recombinant strain IL1043 resulted in 4.8 and 9.7 % decrease in NDF and ADF contents, respectively while the inoculation of silage with strain MG1363 decreased the ADF content by >5 %.

Molecular study on cloned endoglucanase gene from rumen bacterium.

An endoglucanase gene was subcloned from anaerobic rumen bacterium Ruminococcus flavefaciens strain 17. To express endoglucanase gene in Escherichia coli and Streptococcus bovis JB1, an endoglucanase gene fragment was inserted into pVA838-based shuttle vectors. Removal of endoglucanase gene promoter and expression of endoglucanase by promoter of S. bovis JB1 α-amylase gene (pACMCS) was also achieved. Survival of constructs pVACMCI, pTACMC and pACMCS, which carry endoglucanase gene, and stability of endoglucanase gene in S. bovis JB1, were observed. Maximal endoglucanase activities from S. bovis JB1/pVACMCI were 2- to 3-fold higher than from E. coli/pVACMCI. Specific cell activity of E. coli/pACMCS was found to be approximately 2- to -3 fold higher than the both E. coli/pVACMCI and E. coli/pTACMC. Specific cell activity of S. bovis JB1/pACMCS was also found to be approximately 2-fold higher than the both S. bovis/pVACMCI and S. bovis JB1/pTACMC.

Regulation of the acid induciblercfB promoter inLactococcus lactis subsp.lactis

Although Lactococcus is one of the most extensively studied lactic acid bacteria, little information is available on the regulation of the catabolite receptor protein (CRP) and acid induced gene expression. ThercfB gene, encoding RcfB protein which has unknown function in Lactococcus lactis IL1403, was analysed. Promoter region contains consensus CRP binding site and acid inducible sequence at upstream of start site. A 402 bprcfB promoter was fused to upstream of b-galactosidase gene by cloning into promoterless pAK80 plasmid. Promoter activity corresponding to b-galactosidase was measured from Lactococcus lactis IL1403 transformant grown in medium M17 containing different carbon sources. We have found that thercfB promoter expression was highly induced by acidity and carbohydrate sources used in medium and growth phase of the culture.