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Studies of Lactococcus lactis Infection by Phage sk1
Date Issued |
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2016 |
Bacteria Lactococcus lactis is one of the most commonly used in the dairy industry lactic acid bacteria [1]. The infection of these bacteria inhibits lactose conversion to lactic acid. Therefore, quality of the product changes, in some cases the production is stopped. L. lactis is usually infected by bacteriophages belonging to the Siphoviridae family. 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 [2], 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 sk1 suspension was heated at 63°C and 90°C for various time periods. It was observed that heating affects the course of infection: the phage remained infective at 63°C but after 30 min. from the start of the incubation at 90°C, phage was completely inactivated. Multiplicity of infection (MOI) has an influence on the course of infection: the increase of MOI 8 times (from 2 to 16) leaves less unlysed virus-resistant cells. It is known [3] that the supplement of a medium with divalent cations, such as calcium, magnesium, or manganese, is required for the productive infection. Our results also indicated that the reproduction of bacteriopages does not occur if the growth medium is not supplemented with these ions, and Mn2+ ions are the most efficient. L. lactis cells are unable to synthesise heme. The bacterial culture grows longer and produces more biomass after the addition of hemin to the medium. Studies of the infection showed that bacterial lysis progress faster in the medium with hemin. However, after examination of the medium aeration effects on infection, it was discovered that the infection progresses worse at high aeration conditions. [...]