Cold shock proteins of Lactococcus lactis MG1363 are involved in cryoprotection and in the production of cold-induced proteins

Members of the group of 7-kDa cold-shock proteins (CSPs) are the proteins w ith the highest level of induction upon cold shock in the lactic acid bacte rium Lactococcus lactis MG1363. By using double-crossover recombination, tw o L. lactis strains were generated in which genes encoding CSPs are disrupt ed: L. lactis NZ9000 Delta AB lacks the tandemly orientated cspA and cspB g enes, and NZ9000 Delta ABE lacks cspA, cspB, and cspE. Both strains showed no differences in growth at normal and at low temperatures compared to that of the wild-type strain, L. lactis NZ9000. Two-dimensional gel electrophor esis showed that upon disruption of the cspAB genes, the production of rema ining CspE at low temperature increased, and upon disruption of cspA, cspB, and cspE, the production of CspD at normal growth temperatures increased. Northern blot analysis showed that control is most likely at the transcript ional level. Furthermore, it was established by a proteomics approach that some (non-7-kDa) cold-induced proteins (CIPs) are not cold induced in the c sp-lacking strains, among others the histon-like protein HsIA and the signa l transduction protein LIrC. This supports earlier observations (J. A. Wout ers, M. Mailhes, F. M. Rombouts, W. M. De Vos, O. P. Kuipers, and T. Abee, Appl. Environ. Microbiol. 66:3756-3763, 2000). that the CSPs of L. lactis m ight be directly involved in the production of some CIPs upon low-temperatu re exposure. Remarkably, the adaptive response to freezing by prior exposur e to 10 degreesC was significantly reduced in strain NZ9000 Delta AB but no t in strain NZ9000 Delta AB compared to results with wild-type strain NZ900 0, indicating a notable involvement of CspE in cryoprotection.