Isolation, Characterization, and Applicability of Helveticin 34.9, A Class Iii Bacteriocin Produced By Lactobacillus Helveticus 34.9

Abstract

Traditionally fermented foods and beverages are still produced and consumed at a large scale in Romania. They are rich sources for novel lactic acid bacteria with functional properties and with potential application in food industry or health. Lactobacillus helveticus 34.9, isolated from a home-made fermented milk is able to inhibit the growth of other bacteria, such as other lactic acid bacteria, but also strains of Bacillus subtilis, Bacillus cereus, Staphylococcus aureus, and Halobacillus hunanensis, a halobacterium isolated from the degraded wall of a Romanian monastery. L. helveticus 34.9 produces a large bacteriocin (35 KDa), active in a wide pH range, but inactivated by heat and proteinase K treatment. Bacteriocin production was enhanced under stress conditions, especially when combined stresses were applied. Its mode of action and degree of inhibition depended on the indicator strain and on the concentration of bacteriocin that was used. L. delbrueckii subsp. bulgaricus LMG 6901T cells from a suspension were killed within 8 h, but the viability of H. hunanensis 5Hum cells was only reduced to 60%. However, the bacteriocin was able to prevent the bacterial growth of both indicator strains when added to the medium prior inoculation. Scanning electron microscopy images revealed morphological changes induced by the bacteriocin treatment in both sensitive strains, but more severe in the case of L. delbrueckii subsp. bulgaricus. This class III bacteriocin, with inhibitory activity against various bacterial species, may find application in food and non-food related fields, including in the restoration of historical buildings.