Environmental factors for phage-induced fermentation problems: replication and adsorption of the Lactococcus lactis phage P008 as influenced by temperature and pH.

The lactococcal phage P008 was investigated for its growth characteristics under certain environmental conditions. Phage growth was characterized by the latency period, the average burst size (determined in one-step growth experiments) and by the percentage of adsorption to the host cells after 1, 5, 10 and 15 min (determined in modified one-step growth experiments). The incubation conditions studied were temperatures from 20 to 40 degrees C and pH values of 4.8 and 6.4. The growth medium was ultrafiltration permeate of skim milk, which forms the water phase of milk. Both, the temperature and the pH influenced the growth parameters: Increased temperature as well as low pH led to a faster latency along with a higher average burst size. The percentage of adsorption was at maximum when the standard conditions of 30 degrees C and pH 6.4 were applied. Below pH 5, adsorption was reduced to below 10%. A decrease of temperature slightly reduced phage multiplication. Data were incorporated into a model to simulate phage multiplication under certain conditions, taking the percentage adsorption into account. The cell destruction of the host culture was calculated accordingly. The simulation (extrapolation) was validated by experimental growth curves of phages and phage-infected host cultures.