Influence of environmental conditions on Lactococcus Lactis infection with C2 and Sk1 phages

Abstract

Lactococcus lactis is one of the most commonly used in the dairy industry lactic acid bacteria [1]. Virus infection of these bacteria inhibits lactose conversion to lactic acid. Therefore, quality of the product changes, in some cases the production is stopped. Usually L. lactis is infected by phages belonging to the Siphoviridae family. The aim of this study was to determine the influence of phage c2 and sk1 infection on energetical metabolism of L. lactis cells. It is usual in the dairy industry to inactivate bacteriophages by heat [2], but higher the temperature is, more taste and presentation of the final product is affected. In order to explore the phage inactivation by heat, phage c2 and sk1 suspensions were incubated at 63°C and 90°C for various time periods. The heating considerably affected the courses of infections: after 30 min incubation at 63 °C phage sk1 remained infective, but after 30 min at 90 °C this phage was completely inactivated. The infectivity of phage c2 decreases more than 7 times after 15 min of incubation at 90 °C, and after 60 min the phage c2 was completely inactivated. Also our results shows that these phages do not infect heated L. lactis cells. It is known [3] that the supplement of a medium with divalent cations, such as Ca2+, Mg2+, Mn2+ or Sr2+, is rather often required for the productive infection. Our results indicated that the reproduction of phages c2 and sk1 also does not occur if the growth medium is not supplemented with these ions. Also our results have shown that these phages weakly adsorb on L. lactis cells without Ca2+ supplement. Examination of the respiration process have shown that if cells are uninfected, they actively respire and use all the oxygen from the medium. Once the phages c2 or sk1 begins to disrupt cells, the dissolved oxygen concentration in medium gradually increases. Usually L. lactis starter cultures are freeze-dried or spray-dried.[...]