Nisin, lactic acid bacteria production

Modern methods of livestock production are intensive and the environmental conditions stress the animals. The use of antibiotics promotes growth and protects the animals from otherwise certain infection under these conditions. Antibiotic-like compounds formed in lactic acid fermentations prevent proliferation of spoilage and pathogenic microorganisms and increase the shelf life of the products. Nisin is a antimicrobial produced by a lactic acid bacterium and is used in some countries as a food preservative. Some lactic acid bacteria are capable of favorably influencing the fecal flora in man and animals. 

The mechanism(s) by which lactic acid bacteria inhibit or inactivate other bacteria is not totally clear. Daly et al. (1972), Speck (1972), and Gilliland and Speck (1972) have cited evidence which suggests that the following may be involved (1) production of antibiotics such as nisin, diplococcin, acidophilin, lactocidin, lactolin, and perhaps others (2) production of hydrogen peroxide by some lactic acid bacteria (3) depletion of nutrients by lactic acid bacteria, which makes growth of pathogens difficult or impossible (4) production of volatile acids (5) production of acid and reduction in pH (6) production of D-leucine and (7) lowering the oxidation-reduction potential of the substrate. 

In the current industrial process, nisin is manufactured by fermentation of L. lactis subsp. lactis in a milk-based medium. Biosynthesis of nisin is coupled with the growth of lactic acid bacteria and the production of a significant amount of lactic acid (7). Lactic acid is an important chemical for food processing. It can also be used as a raw material in the production of the biodegradable polymer poly(lactic) acid (12). Unfortunately, lactic acid is not recovered in the current nisin process. 

Radler, F. (1990b). Possible use of nisin in winemaking. 11. Experiments to control lactic acid bacteria in the production of wine. Am. J. Enol. Vitic., 41, 7-11. 

The first report of the production of a bacteriocin produced by lactic acid bacteria was made in 1928 [24]. The substance was determined as a polypeptide [25] and subsequently named nisin [26,27]. Since that time the bacteriocin field has expanded exponentially, and now bacteriocins produced by all genera of the lactic acid bacteria have been reported [1,21]. 

Lactic acid bacteria have been proposed as cell factories in a number of applications targeting either in vitro production and subsequent purification of biomolecules, or in vivo delivery of biomolecules in hosts by the LAB itself (Hugenholtz et al. 2002 LeBlanc et al. 2005 Morello et al. 2008). The bacteriocin nisin, whose industrial use as additive has been approved in a number of countries worldwide (Cleveland et al. 2001), is produced by some L. lactis strains. Attempts to boost nisin production using L. lactis biofilm reactors allowed both a ca. 2-fold increase in nisin production compared to the level obtained in a suspended-cell reactor and a drastic reduction in the lag phase of nisin production (Pongtharangkul and Demirci 2006). 

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