Studies of Lactococcus lactis infection by phage C2

Abstract

Bacteria Lactococcus lactis is one of the most commonly used lactic acid bacteria in the dairy industry [1]. It is used in the production of cheese, sour cream, yogurt, buttermilk, and other dairy products. L. lactis is usually infected by bacteriophages belonging to the Siphoviridae family and are divided into three main groups: 936, c2, and P335. Due to bacteriophage-caused infections the dairy industry experiences substantial loss of income [2]. The infection inhibits lactose fermentation to lactic acid. Therefore, quality of the product changes, in some cases the production is stopped. The aim of this study was to determine the influence of incubation conditions on L. lactis viral infection. It is usual in the dairy industry to inactivate bacteriophages by heat [3], but higher the temperature is, more taste and presentation of the final product is affected. In order to explore the bacteriophage inactivation by heat, not the infected bacterial culture but the bacteriophage suspension was heated. Bacteriophage c2 suspension was heated at 63°C for various time periods. It was observed that heating affects the course of infection: the phage remained infective, but the infection process took longer. Multiplicity of infection (MOI) examination has shown that MOI has a significant influence on the course of infection: the increase of MOI 10 times (from 5 to 50) leaves less unlysed virus-resistant cells. It is known [4] that the supplement of a medium with calcium ions is required for a efficient infection. Our results also indicated that the productive infection did not occur if the growth medium was not supplemented with calcium ions. L. lactis bacteria are unable to synthesise heme. The bacterial culture grows longer and produces more biomass afer the addition of hemin to the medium Studies of the infection have shown that bacterial lysis progress faster in the medium with hemin. [...]