Bacteriocin: the avenues of innovation towards applied microbiology

Microbial adhesion and pathogenesis result in serious problems in world. In case of infectious diseases in human being, there is an epidemiological issue, on another hand, if microbes infect poultry and crops, there is a huge economical and nutritional loss. Antibiotics used to control this microbial pathogenesis but the excess use of antibiotics and other chemical compounds in intensive animal production have several side effects and results in increased antibiotic resistance day by day. Antimicrobial resistance becomes a great problem in the world. Scientists are seeking for the product which can be used as alternative to the antibiotic with less side effects. Bacteriocin is such a type of peptide which works when bacteria become resistant to some antibiotic. It is ribosomaly synthesize antimicrobial peptide by gram positive and gram-negative bacteria. Various types of bacteria produce different type of bacteriocins. They have different antimicrobial spectrum. Spectrum of antimicrobial activity varies from bacteria to bacteria. Due to their proteinaceous nature they are harmless to human gastrointestinal tract. Bacteriocins are used to treat many infectious diseases in animals and human beings. It has wide application in food industry to prevent the growth of pathogenic bacteria. Nisin was the first bacteriocin used in the food as the research advances novel bacteriocins introduced which are being used in food industry for the preservation of food. Moreover, it has wide application in pharmaceutical industry. Bacteriocins are gaining attention in the recent era due to their unique mode of antimicrobial action and wide application in various industries.


Review Article
Bacteriocin: the avenues of innovation towards applied microbiology Introduction Food spoilage due to microbial adhesion is a great problem.Due to food spoilage there is not only a nutritional loss but also an economical loss [1].Chemical preservatives are not appropriate due to their hazardous effects on human health.It is very important to resolve this problem to fulfill the food requirement of rising world.In this era, natural and microbiological methods are being used to preserve the food [2].To manage the economic loss, use of bacteriocins as preservative in the food industries is a satisfactory approach.In the recent world, bacteriocins application are gaining interest as they are generally regarded as safe (GRAS) by the food authority and World health organization [3].
Moreover, bacteriocins due to its proteinaceous nature implies a putative degradation in gastrointestinal tract of human beings [4] therefore, these bacteriocins aid colonization in the digestive system [5].Function of peptides can be affected by various factors including proteolytic degradation, non-polar and polar food components and fat contents, sodium chloride concentration and pH [6].Bacteriocins are not only effective against the closely related organisms but also effective against organisms like mycobacterium, viruses and fungi.Its potential applications have been studied specially in food industry as bio preservative from many years [7], [8].Moreover, bacteriocin as an antimicrobial agent has been exploited in various fields as their influence against various pathogen related to veterinary and human disease [9], [10], [11].

Background of bacteriocins
It was first reported in 1925, that the antibacterial substance produced by the E. coli have capacity to inhibit the other strains of same species reported by André Gratia [12].It was thought that the compound produced from bacteria called colicin and are responsible for the inhibitory effect.After that in 1928, it was observed certain Lactococci strains ability to inhibit other LAB strains [13].According to Mattick and Hirsh, studies in 1947 [14], Lactococcus lactis subsp.Lactis produced an inhibitory substance which called as nisin which has inhibitory effect on prokaryotes [15].In 1953, nisin was initially marketed, purified and termed as bacteriocin [16] and regarded as safe Food Additives in 1969 by the Joint / World Health Organization Expert Committee/ Food and Agriculture Organization.In the list of food additives, nisin was added in Europe in 1983 and it was used in processed cheese authorized by the American Food and Drug Administration (FDA) in 1988 [17].Firstly, nisin was approved to be used in food by FDA while as the research advances pediocin have also been used in industrialized foods as preservative obtained from Pediococcus parvulus, Pediococcus acidilactici and Lactobacillus plantarum WHE92 [18].As reported by Yi [19] Lactobacillus crustorum MN047 synthesize a bacteriocin BMP11 which has a rich α-helix confirmation.Bacteriocin was purified through HPLC (high performance liquid chromatography) and ion exchange chromatography and when it tested against food borne pathogen showed minimum inhibitory concentration MIC value of 0.3-38.4μg/ml.Moreover, it was noted that BMP11 had a bactericidal mode of action.Transmission electron microscope and scanning electron microscope (SEM) results showed that BMP11 destroyed the pathogen cell envelop integrity with cell membrane permeability ad cell wall perforation.
Cells envelop integrity destruction further identified through lactic dehydrogenase release and propidium (PI) uptake.Meanwhile, in milk it inhibits the growth of Listeria monocytogen and exhibits the antibiofilm formation activity.Therefore, BMP11 has a potential to act as antimicrobial and used as preservative to control the foodborne pathogen in dairy product

Conclusion
Bacteriocins are the antimicrobial peptides synthesized by bacteria for their survival.These extracellular peptides are very beneficial on industrial scale.They exhibit the ability to inhibit the wide variety of microorganisms.They not only inhibit the growth of closely related bacteria but also have ability to inhibit the growth of viruses and fungus.The ability of bacteria to produce bacteriocin which have inhibitory spectrum might be used for the welfare of human beings and their efficacy in pharmaceutical industries might be exploited by enhancing its production by bacteriocin engineering.However, shifting the antimicrobial spectrum increases potency and stabilization is still a challenging field.Computational approaches to revolutionize the bacteriocin potency through chemical and biological modification are also on way, but more research is needed to explore the behavior and utility of bacteriocin on commercial scale.Future implications of bacteriocins can led to the avenues of innovation for different industries.

Authors' contributions
[19].Classes of bacteriocins The heterogenous group which are peptides synthesized ribosomally [3] mainly divided into three classes, I II and III [20] but advanced studies further categories them into further classes and subclasses.They are classified on the basis of their structural and physiochemical properties.Recently bacteriocins have been divided into four categories.Class I bacteriocins, the lentibiotics [21] are broad spectrum peptides like nisin; inhibit the growth of gram-positive spoilage microbes and food borne pathogens.Class II bacteriocins are the small heat stable non lantibiotics which have narrow antimicrobial spectrum.Garviecin LG34 is a class II bacteriocin consisting of 46 amino acid residues which exhibit inhibitory activity against gram negative and grampositive bacteria.Enterocin CRL35 is another class II bacteriocin with anti-Listerial activity [6], [22].Class III bacteriocins are large heat labile, break down the cell wall of bacteria in an enzymatic manner and are usually endopeptidase.Class IV bacteriocins are composed of lipids, carbohydrates and an undefined mixture of protein [21].Class IV bacteriocins are complex bacteriocins and are sensitive to lipolytic and glycolytic enzymes like leuconocin S and plantaricin S. Mode of action of bacterial bacteriocins Antimicrobial peptides produced by prokaryotes that kills or inhibit phylogenetic related microorganisms are called bacteriocins [23].The action of bacteriocins may be as antimicrobial, colonizing or signaling peptides [24].They mostly form pores on the cell membrane of pathogen whereas their proteinaceous nature let them degrade efficiently and rapidly.Thus, the chance of developing resistance like antibiotics become minimized [22].Lactic Acid Bacteria (LAB) are studied extensively due to their potential in bio-preservation by producing bacteriocins [8, 24].It has been predicted that∼99% of all bacteria synthesize at least one bacteriocin, with a length of minimum10 amino acids or as long as 688 residues [25].However, due to multidrug resistance of bacterial clinical strains, the use and application of bacteriocins is gaining more interest [23].Since the past decade, the reported bacteriocin number has been increased significantly.The high potential of these antimicrobial peptides has expended uses in the pharmaceutical and food industries, in apiculture and agriculture [23, 26].In recent years, attention is given towards these antimicrobial compounds as they are significant as bio-preservative and substituted for chemical preservatives used in food.They have potential to improve the shelf life of food as well.The equilibrium is attained by their inhibitory activity upon pathogenic bacteria [21].Different types of bacteria produce different types of bacteriocins that make them distinct from other species of bacteria.Bacteriocins synthesized by LAB (Lactic Acid Bacteria) have variable spectrum of activities.Many bacteriocins are small sized molecules with high isoelectronic points and amphipathic characteristics [27].The cell produces bacteriocins have specific immunity proteins due to which they are resistant to these antimicrobial peptides [24, 27-29].LAB (Lactic acid bacteria) are very crucial as they prevent the growth of pathogenic [30] as well as spoilage microbes in food product through the production of acids and antimicrobial agent thus improve the quality and safety of fermented foods [7, 31, 32].Two LAB species Lactobacillus sakei and Lactobacillus curvatus plays significant role in the accelerated maturation of fermented meat products and improve flavor.These two species are present in a variety of fermented meat products as their microbiota.The action of bacteriocin is similar that they replace the structural protein or by bacteriocin antagonistic competition for the receptor [7, 33].A recent study revealed that the bacteriocin receptor altered with the bacterial membrane structural modifications [34].Moreover, it was noticed that the additive used with bacteriocin significantly increases it activity [35].Various classes of bacteriocins have different mode of actions and functions.Functions of class I bacteriocins are to disrupt the membrane of the target (pathogens) by interaction of the peptide with the chiral receptor [36], they are ribosomally produced and post translational peptides (RiPPs), during their biosynthesis they undergo enzymatic modification [3].In case of class II, cleave the peptide tab.or membrane translocation is facilitated by accessory proteins.

68]. Bacteriocins: A natural way to combat with pathogens
Bateriocins are the peptides which interfere with the structural proteins of the target pathogen.The interaction of various classes of bacteriocins with its target is diverse.However, the conjugation of bacteriocins with the incorporation of drug delivery system is recently expanding field [69].Bacteriocin is considered as "designer's drugs" that means they attack on specific pathogen [70].Bacteriocins have ability to tolerate acidic condition in acidic environment of gastrointestinal tract GIT.It can be applied to control the growth of lethal microorganisms like L. monocytogen.However, in Amado study [71] it was reported that the use of bacteriocin (pediocin SA-1) have ability to inhibit the growth of L.

Table 1 . Bacterial species producing bacteriocins against pathogen Pathogen reported Bacterial species producing bacteriocin Reference
Now a days, bacteriocins are also used to preserve the grains [115] and also used to control pest in the field.As reported by Tsuda [116] lactic acid producing bacteria Lactobacillus plantarum strain BY reduced the soft rot disease in Chinese cabbage.This strain is also used to control disease in potato, tomato and onion.After the spray of Lactobacillus plantarum strain BY on Chinese cabbage leave it persisted on wound and inhibit the growth of pathogens while it also proliferates in the host tissue [116].The results indicated the application of Lactic Acid Bacteria as a biological control as well as biofertilizer in agriculture.They directly promote the seed germination or plant growth and alleviate numerous abiotic stresses [117].