Sugar citrate cometabolism in Leuconostoc mesenteroides

Bacteria from the genus Leuconostoc play roles in the dairy industry. The m ost important functions of this bacteria are their ability to produce CO2 a nd flavour compounds through lactose heterofermentation and citrate utiliza tion. Although the biotechnological role of the citrate metabolism is very important and widely appreciated, little is known about the genetic propert ies of Leuconostoc spp. In our laboratory, we cloned the genes responsible for citrate metabolism (clyR mae citCDEFGOP cluster), for D-lactate dehydro genase (ldhD) and for phosphotransacetylase (pta). In addition we have plan ned to construct new vectors and we have tried to improve a method to intro duce recombinant DNA molecules into Leuconostoc as well. Characterization o f the plasmid involved in this study is still in progress. The nucleotide s equence analysis of p22R revealed the presence of C5 cytosine methylase gen e typical of type II restriction/modification system. The low transformatio n efficiency of some strains of Leuconostoc may be due to the presence of t hat plasmid. The construction of the defective strain for restriction activ ity could be very useful to genetic manipulations of Leuconostoc in the fut ure.