Cotransformation of lactococcin-producing, 2.0-mega dalton and erythromycin-resistant pGB 301 plasmids toLactococcus lactis subsp.lactis protoplast

A coelectroporation method for the isolation of cryptic plasmids from Lactococcus lactis

AIMS

A coelectroporation method using a marker plasmid for indirect selection of lactococcal plasmids with unassigned functions was evaluated.

METHODS AND RESULTS

Cryptic plasmids were mixed with an erythromycin resistance (Eryr) marker plasmid and introduced into a recipient strain by electroporation, followed by plasmid extraction of erythromycin-resistant transformants. By optimizing the ratio between the marker plasmid and the cryptic plasmids, an average of 20% cotransformants was obtained, including combinations of more than one cryptic plasmid. The marker plasmid pSA3 was easily eliminated from the cotransformed cells by subculture without selective pressure.

CONCLUSION

This cotransformation approach reduces the number of colonies that must be screened to find transformants harbouring cryptic plasmids.

SIGNIFICANCE AND IMPACT OF THE STUDY

The method facilitates the isolation of cryptic plasmids, helps in assigning functions to unknown plasmids and allows construction of food-grade lactococcal strains with new combinations of wild-type plasmids.

Antifungal attributes of lactic acid bacteria--a review

Molds constitute a very important contaminating flora of dairy products. Contamination with undesirable molds has been a serious and frequently disturbing problem in the dairy industry that results in huge losses due to spoilage of cheese and other fermented foods incriminated by a variety of mycoflora such as Aspergillus, Penicillium, Fusarium, Rhizopus, and Mucor. The considerable drop in pH caused by the growth of lactic acid bacteria (LAB) in fermented milk makes such foods a breeding ground for the highly opportunistic fungi to proliferate and thrive, spoiling the products and effecting cost and its commensurate accessories. The major antimicrobial substances isolated from the LAB are found effective against bacteria only and their inhibition toward the growth of contaminating bacteria has been explored in detail. However, studies on the fungistatic properties of LAB are relatively rare. This article reviews the investigative studies on the antifungal aspects of different lactic acid bacteria and the prospects of this exceptional trait as a potential food biopreservative.