Simultaneous lactic acidification and coagulation by using recombinant Lactococcus lactis strain

AIMS

This study was an attempt to create a novel milk clotting procedure using a recombinant bacterium capable of milk coagulation.

METHODS AND RESULTS

The Rhizomucor pusillus proteinase (RPP) gene was sub-cloned into a pALF expression vector. The recombinant pALF-RPP vector was then electro-transferred into Lactococcus lactis. Finally, the milk coagulation ability of recombinant L. lactis carrying a RPP gene was evaluated. Nucleotide sequencing of DNA insertion from the clone revealed that the RPP activity corresponded to an open reading frame consisting of 1218 bp coding for a 43·45 kDa RPP protein. The RPP protein assay results indicated that the highest RPP enzyme expression with 870 Soxhlet units (SU) per ml and 7914 SU/OD were obtained for cultures which were incubated at pH 5·5 and 30°C. Interestingly, milk coagulation was observed after 205 min of inoculating milk with recombinant L. lactis carrying the RPP gene.

CONCLUSION

The recombinant L. lactis carrying RPP gene has the ability to function as a starter culture for acidifying and subsequently coagulating milk by producing RPP as a milk coagulant agent.

SIGNIFICANCE AND IMPACT OF THE STUDY

Creating a recombinant starter culture bacterium that is able to coagulate milk. It is significant because the recombinant L. lactis has the ability to work as a starter culture and milk coagulation agent.

Metabolic engineering of Lactococcus lactis influence of the overproduction of lipase enzyme

The dairy industry uses lipase extensively for hydrolysis of milk fat. Lipase is used in the modification of the fatty acid chain length, to enhance the flavours of various chesses. Therefore finding the unlimited source of lipase is a concern of dairy industry. Due to the importance of lipase, this study was an attempt to express the lipase from Burkholderia cepacia in Lactococcus lactis. To achieve this, a gene associated with lipase transport was amplified and subcloned in inducible pNZ8148 vector, and subsequently transformed into Lc. lactis NZ9000. The enzyme assay as well as SDS-PAGE and western blotting were carried out to analysis the recombinant lipase expression. Nucleotide sequencing of the DNA insert from the clone revealed that the lipase activity corresponded to an open reading frame consisting of 1092 bp coding for a 37·5-kDa size protein. Blue colour colonies on nile blue sulphate agar and sharp band on 37·5-kD size on SDS-PAGE and western blotting results confirm the successful expression of lipase by Lc. lactis. The protein assay also showed high expression, approximately 152·2 μg/ml.h, of lipase by recombinant Lc. lactis. The results indicate that Lc. lactis has high potential to overproduce the recombinant lipase which can be used commercially for industrially purposes.