Bacteriocins: Biosynthesis, Production, Purification, and Its Potential Applications in Food and Human Health

ABSTRACT

Bacteriocins are antimicrobial compounds produced naturally by bacteria. While antibiotics are antimicrobial compounds with broad-spectrum activity, bacteriocins are effective only against related species of the producer strain. The lactic acid bacteria (LAB) are employed as bio-preservatives in the food industiy as they are the main producers of bacteriocins. Some bacteriocins are extracted and purified while some are used in crude fonn. Currently, there is a wide interest in the isolation of novel extracellular bacteriocins. Some of the important production parameters affecting the production of bacteriocins include pH, temperature, agitation, inoculums level, incubation time, sources of carbon and nitrogen, and its content. Agro-industrial by-product such as whey, com steep liquor, potato starch liquor, deoiled rice bran, molasss, pea pod, soya okra, and kiimow peel have been studied to be used as a substrate for its production. Recovery and purification strategies such as ultrafiltration, salting out, ion- exchange, Sodium Dodecyl Sulfate Polyacrilamide Gel Electrophoresis (SDS PAGE), solvent extraction, adsorption-desorption, size exclusion chromatography, and reverse-phase high performance liquid chromatography (RP-HPLC) have studied so far. Nisin is a bacteriocin used commercially with great success. Besides the food industiy, they have a great potential in veterinary medicine. These can also be used for enhancing the shelf life of processed foods and as animal growth promoter. This chapter aims to put together comprehensive information on the recent advances associated with biosynthesis of bacteriocins and its production and application in human welfare.

INTRODUCTION

Bacteria (gram-positive, gram-negative and some archaea), during their primary phase of growth, produce antimicrobial substances which are proteinaceous in nature. These naturally produced substances are known as bacteriocins. These ribosomally synthesized antibacterial peptides affect genetically related species or across genera of bacteriocin producers (Todorov et al., 2011). They contain lysyl and arginyl residues in excess, making them cationic and amphipathic in nature. These are secondaiy metabolites of low molecular weight (LMW) of approximately 10 kDa. Like other proteins, bacteriocins also undergo post-translational modification. Proteolytic enzymes like protease of mammalian gastrointestinal tract can easily degrade them. This makes it fit for human consumption. Bacteriocins are among the best-studied microbial defense systems. Bacteriocins, like chemical mediators, also help in quorum sensing as well as in communication within bacterial consortia (Mantovani et ah, 2011).

Bacteriocin producers are found in different ecosystems like soil, human gastrointestinal tract as its natural microflora and animals, as the normal microbiota of vegetables, fruits, food products like fermented meat products, fermented vegetables, and fermented fruits (Todorov et al., 2010). They survive in different ecological niches and form communities because of the production of anti-competitor compounds (Balakrishnan et al., 2002; Kerr et al., 2002; Bukard et al., 2007). They belong to different systematic groups.

In the food industry, the main source for bacteriocins is lactic acid bacteria (LAB). Some of the most important bacteriocin producers are Lactobacillus, Bifidobacterium, Lactococcus, Pediococcus, Enterococcus, Oenococcus, Streptococcus, Tetragenococcus, Carnobacterium, Vagococcus, Propi- ouibacterium, and Leuconostoc. Bacteriocins are divided into four major classes. Lantibiotics are called class I bacteriocins and Nisin belongs to this group. Class II includes bacteriocins which are less than 10 kDa in mass and are thermostable. They have antilisterial property and have potential as a food preservative. This group also includes circular bacteriocins and they affect the membrane integrity and cell wall formation of target cells. Class

III bacteriocins are thermolabile with the mass of 30 kDa or more. Class

IV bacteriocins are glycoproteins or lipoproteins in nature and are hydro- phobic and heat-stable (Mortvedt et al., 1991; Nes and Holo, 2000; Alpay et al., 2003). Gram-negative bacteriocin producing bacteria belong to the family Enterobacteriaceae. Examples are colicins and microcins produced by Escherichia coli. Some members of archaea produce archaeocins called halocins and sulfolobicins. Halocins are produced by members of family Halobacteriaceae and sulfolobicins by Sulfolobales (Atanasova et al., 2013).

The aim of the chapter entitled “Bacteriocins: Biosynthesis, production, purification, and applications” focuses on recent advances associated with biosynthesis of bacteriocins and its production and application in preservation of foods and modulating the starter cultures in the fermented foods.

 
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