روش های بیوتکنولوژی جدید در باکتریوسین: مقاله مروری Novel biotechnological applications of bacteriocins: A review

۱٫ Introduction Lactic acid bacteria (LAB) are a diverse and very useful group of bacteria that, while not adhering to a strict taxonomic group, are gathered on the basis of shared properties (Oguntoyinbo & Narbad, 2012) and have the common trait of producing lactic acid (LA) as a major or sole fermentation product. For these reasons, LAB have historically been associated with the fermentation of foods, and as a result many LAB, like Lactococcus, Oenococcus, Lactobacillus, Leuconostoc, Pedicoccus and Streptococcus sp., are generally recognized as safe (GRAS) and/or probiotics (Mayo et al., 2010). The desirable property of a probiotic strain is the ability to produce antimicrobial substances such as bacteriocins that offer the potential to provide an advantage in competition and colonization of the gastrointestinal tract. Bacteriocins are generally defined as peptides produced by bacteria that inhibit or kill other related and unrelated microorganisms. Bacteriocin was firstly identified by Gratia (1925) as an antimicrobial protein produced by Escherichia coli and named colicin. The interest in bacteriocins produced by GRAS microorganisms has been leading to considerable interest for nisin, being the first bacteriocin to gain widespread commercial application since 1969. As a result, the field has developed increasingly, resulting in the discovery and detailed characterization of a great number of bacteriocins from LAB in the last few decades (Collins, Cotter, Hill, & Ross, 2010). Nowadays, consumers are aware of the health concerns regarding food additives; the health benefits of “natural” and “traditional” foods, processed without any addition of chemical preservatives, are becoming more attractive. Thus, because of recent consumer demand for higher quality and natural foods, as well as of strict government requirements to guarantee food safety, food producers have faced conflicting challenges (Franz, Cho, Holzapfel, & Gálvez, 2010). Chemical additives have generally been used to combat specific microorganisms. The application of bacteriocins as biopreservatives for vegetable food matrices started approximately 25 years ago. In these years, a lot of studies have focused on the inhibition of spoilage and/or human pathogens associated with vegetable foods and beverages by bacteriocins, and their application appeared as a good alternative to chemical compounds and antibiotics. When deliberately added or produced in situ, bacteriocins have been found to play a fundamental role in the control of pathogenic and undesirable flora, as well as in the establishment of beneficial bacterial populations (Collins et al., 2010). Traditionally, new bacteriocins have been identified by screening bacterial isolates for antimicrobial activity followed by purification and identification of the bacteriocin and its genetic determinants. Such a strategy is still fundamental for detection and identification of powerful bacteriocins of various subclasses, and recent examples of this include a) a class IIa bacteriocin named avicin A that was identified from Enterococcus avium strains isolated from faecal samples of healthy human infants from both Ethiopia and Norway (Birri, Brede, Forberg, Holo, & Nes, 2010), b) a circular bacteriocin named garvicin ML produced by a Lactococcus garvieae strain isolated from mallard duck (Borrero et al., 2011), c) a class IIb bacteriocin named enterocin X isolated from an Enterococcus faecium strain from sugar apples (Hu, Malaphan, Zendo, Nakayama, & Sonomoto, 2010) and d) a glycosylated bacteriocin (glycocin F) from Lactobacillus plantarum isolated from fermented corn (Kelly, Asmundson, & Huang, 1996). In the next sections, we will present bacteriocin classification, their mode of action and structure, biotechnological applications in food and pharmaceutical industries and problems associated with resistance and purification. ۲٫ Classification According to Klaenhammer (1993), bacteriocins can be divided into four classes. The class I of lantibiotics, represented by nisin, gathers very low molecular weight (<5 kDa) thermostable peptides characterized by the presence of lanthionine and derivatives. The class II is composed of small thermostable peptides (<10 kDa) divided into three subclasses: IIa (pediocin and enterocin), IIb (lactocin G) and IIc (lactocin B). The class III is represented by high molecular weight (>30 kDa) thermolabile peptides such as the helveticin J, while in the class IV we can find large peptides complexed with carbohydrates or lipids. However, Cleveland, Montville, Nes, and Chikindas (2001) believe that these structures are artifacts of partial purification and not a new class of bacteriocins. Cotter, Hill, and Ross (2005) suggested a new classification where bacteriocins are divided into two categories: lantibiotics (class I) and not containing lanthionine lantibiotics (class II), while high molecular weight thermolabile peptides, which are formally components of the above class III, would be separately designated as “bacteriolysins”. These authors also suggested that the above class IV should be extinguished. Finally, Drider, Fimland, Hechard, Mcmullen, and Prevost (2006) divided bacteriocins into three major classes according to their genetic and biochemical characteristics (Table 1), and we will refer to such a classification in the following.