# The Role of Microorganisms and Their Antibacterial Compounds in Food Biopreservation
## 3 Antimicrobial Compounds Produced by Bacteria
### Bacteriocins  
Bacterial metabolites, i.e., purified or semi-purified bacteriocins can also be employed to counteract undesired spoilage or pathogenic bacteria. Bacteriocins are small polypeptide molecules ribosomally synthesized by many species of Gram-positive and Gram-negative bacteria and archaea. Bacteriocin synthesis is encoded in transferable bacteria elements such as plasmids and transposons [28; 29]. Bacteriocins are harmful to competing microorganisms of ecological niches. Cytotoxicity can be very specific, dependent on its concentration and the nature of the targeted cell. The spectrum of antibacterial activity is narrow. Generally, the most sensitive species of bacteria are those related to bacteriocin strains. Bacteriocins were discovered by [PERSON] in 1925. The first isolated bacteriocin was colicin derived from Gram-negative bacteria _Escherichia coli_[30]. To capture the diversity of many bacteriocins, a few attempts at classification systems were proposed. The first bacteriocin classification was introduced by [PERSON] in 1993 [28]. The classification proposed by [PERSON] et al. captures all the bacteriocin isolated from the Gram-positive bacteria [31]. Another classification introduced by [PERSON] et al. divided bacteriocins from Gram-positive and Gram-negative bacteria into two large groups: class I of molecular mass <5 kDa including lanthipeptides, sactiepeptides, circular peptides, and glycocins, and class II of molecular mass 6-10 kDa. Bacteriocins of class I compared to class II are more stable to physicochemical factors such as high temperatures and extreme pHs, and more resistant to proteolytic enzymes [32]. Bacterios are a diverse and growing group of antimicrobial peptides produced by a wide range of bacteria. Therefore, to assemble available information and better categorize them, open-access databases were created (Table 1). The primary target for bacteriocins is the cell membrane. Cell membrane disruption is a major antimicrobial mechanism of bacteriocins. They attack bacterial membrane surface charge and membrane fluidity binding by anionic lipids. Cell permeabilization and pore formation cause the efflux of cytoplasm and, in turn, lead to cell death--a bactericidal effect [42; 43; 44; 45]. The bacteriostatic activity of bacteriocins is due to the interaction with DNA gyrase, RNA polymerase, and other essential cellular macromolecules. Bacteriogenic bacteria are equipped with a protection mechanism against bacteriocins. This protection is ensured by a combined system of efflux pumps transporting bacteriocins outside the cell and by immunity proteins [46; 47]. According to the crucial issue that is food safety, the most valuable in the food industry bacteriocin species are those which effectively reduce the occurrence of spoilage microorganisms and foodborne pathogens. However, they can also be harmful to the beneficial microbiota. Therefore, the selection of bacteriocins should consider that the beneficial microorganism naturally present in various foods (i.e., fermented food) or added as an adjunct culture (i.e., probiotics) ought to be unaffected [47]. On the other hand, the level of bacteriocin or producing bacteriocin strains should remain at the appropriate level in food to ensure the antimicrobial effect. The antimicrobial activity of bacteriocins can be diminished by physicochemical stresses occurring at different steps of food processing. However, some of them were shown to be stable at low pH and high temperatures, and tolerate a wide spectrum of salt concentrations [48]. Bacteriocins can also be destroyed by proteolytic enzymes synthesized by competitive microorganisms [49]. According to [PERSON] et al.