Bacteria living in microbial communities use several functions and strategies to survive or coexist with other microorganisms, competing to obtain nutrients and colonize space in their habitat (Hibbing et al. 2010). One of the strategies used by bacteria to guarantee their growth in communities is antagonism, which effectively limits the growth of other microorganisms (Russel et al. 2017). To accomplish antagonism, bacteria must produce inhibitory substances such as antibiotics, organic acids, siderophores, volatile organic compounds, antifungals, and bacteriocins (Riley 2009). In addition to inhibiting the growth of other microorganisms, bacteriocins have different traits that make them attractive for biotechnological applications. For example, while resistance against nisin exists, in general, the bacteriocin mechanism of action less often induces resistance as it happens with conventional antibiotics (Behrens et al. 2017). Furthermore, some bacteriocins are compounds produced by the natural host-associated microbiome; therefore, they are harmless to the host. Bacteriocins also show selective cytotoxicity toward cancer cells compared to normal cells (Kaur and Kaur 2015).
Bacteriocins are antimicrobial peptides synthesized by the ribosome representing the most abundant and diverse group of bacterial defense systems (Silva et al. 2018). Bacteriocins were considered to have a narrow antimicrobial spectrum that could only inhibit bacterial strains closely related to produced bacteria; however, several studies have shown that there are bacteriocins able to kill different genera of bacteria and even certain yeasts, parasites, and cancer cells (Kaur and Kaur 2015; Baindara et al. 2018).
The success of bacteriocins in eliminating multidrug resistant pathogens (MDR) has led to medical applications to treat bacterial infections.
Bacteriocins of Gram-positive bacteria are cationic and amphiphilic molecules whose mass varies from < 5 to more than 30 kDa (Balciunas et al. 2013) (Fig. 1). Many classifications of bacteriocins are available, but their diverse chemical structures and inhibitory activities make their classification into a specific group quite difficult. Class I bacteriocins, also known as lantibiotics, contain in their primary structure uncommon amino acids like lanthionine, β-methyl lanthionine, and dehydroalanine. These unique amino acids formed by post-translational modifications can provide antimicrobial activity and peptide stability. For example, they can create covalent bridges that result in internal rings that give stability to the peptide structure. In addition, internal rings contribute to the formation of a secondary structure in water that favors antimicrobial activity (Almeida and Pokorni 2012). Around 30% of lantibiotics already identified have been purified from lactic acid bacteria, including the well-known nisin, mersacidin, and lacticin 3147 (Stoyanova et al. 2012). The class II bacteriocins are membrane-active and heat-stable peptides known as non-lantibiotics or pediocin-like antibiotics (Balandin et al. 2019). They do not harbor modified amino acids, and their molecular weights are lower than 10 kDa. Prototype bacteriocins of this group are pediocin PA-1, pentocin 31–1, enterocin P, sakacin G, enterocin A, two-peptide components (enterocin DD14, plantaracin E/F), sec-dependent secreted (acidocin B), and other not yet subclassified (bactofencin A peptides) (Liu et al. 2008; Balandin et al. 2019; Ladjouzi et al. 2020). The class III bacteriocins are large (> 30 kDa) heat-labile peptides composed of an N-terminal endopeptidase domain and a C-terminal substrate recognition domain. Bacteriocins of this group can lyse the cell wall of sensitive bacteria, although there are non-lytic bacteriocins in this group too, like helveticin J. Some examples of Class III bacteriocins are helveticin M, zoocin A and enterolysin A (bacteriolysins), and millericin B (murein hydrolase) (Alvarez-Sieiro et al. 2016; Sun et al. 2018). Class IV are complex peptide structures associated with lipid and carbohydrate moiety forming glycoproteins and lipoproteins. These structural characteristics make them sensitive to the action of glycolytic or lipolytic enzymes. Lactocin 27 and leuconocin S are prototype bacteriocins of this group and are recognized to disrupt bacterial cell membranes (Simons et al. 2020). Class V includes cyclic peptide structures like enterocin AS-48, pumilarin, lactocyclicin Q, and plantaricyclin A (Perez et al. 2018; Sánchez-Hidalgo et al. 2011). The circular nature of their structures provides Class V with superior stability against several stresses compared to most linear bacteriocins. Biosynthesis of circular bacteriocins involves cleavage of the leader peptide, circularization, and export to the extracellular space.
Gram-negative bacteria produce both high molecular weight (> 30 kDa) and low molecular weight (< 10 kDa) bacteriocins (Rebuffat 2016). The first bacteriocin identified from a Gram-negative bacterium was colicin, produced by
Microcin mJ25 produced by
Tailocins are bacteriocins like phage tails and display a rigid or flexible structure, similar to R-type and F-type pyocins. Tailocins with contractile and flexible tail morphologies are designated as myotailocins and siphotailocins, respectively (Yao et al. 2017). These bacteriocins have been described in plant-associated
Lectin-like bacteriocins (LlpAs) represent another type of antimicrobial protein secreted by members of the genus
Bacteriocins exert several mechanisms of action towards Gram-positive and Gram-negative bacteria (Fig. 3). Class I bacteriocins produced by Gram-positive bacteria permeabilize bacterial membranes through pore-formation, leading to ion leakage and cell death. These include bacteriocins produced by
The mechanism of action of Gram-negative bacteriocins, such as colicins, is through recognizing cell surface receptors of a target cell, through the Tol or TonB machinery, as shown in Fig. 3b. Colicins C domain (cytotoxicity domain) is responsible for eliminating other microorganisms through various mechanisms such as membrane permeabilization, nuclease activity, and inhibition of peptidoglycan or lipopolysaccharide O-antigen synthesis (Budič et al. 2011).
The genus
Pyocins have a limited antimicrobial spectrum, mainly inhibiting competitors highly related to the producer strain (Redero et al. 2018). However, some R-type pyocins can inhibit other species such as
LlpAs have a selective mechanism of action, different from other bacteriocins produced by
Bacteria can take up exogenous DNA and incorporate it into their genome through a process termed competence. Competent bacteria can use absorbed DNA as a source of nutrients, DNA reparation, or recombination with the genome. Natural DNA transformation happens when absorbed DNA is integrated into the genome (Veening and Blokesh 2017). This process is considered the primary mode of horizontal gene transfer (HGT) in bacteria, along with conjugation (direct cell to cell transfer of DNA via a specialized conjugal pilus) and phage transduction (DNA transfer mediated by viruses). Naturally competent bacteria couple the DNA-uptake process with other physiological responses, such as growth arrest and synthesis of antimicrobial polypeptides (bacteriocins) (Mignolet et al. 2018). Bacteria secrete bacteriocins upon entry into the competence state to kill surrounding competitors.
The competence pathway in
Bacteriocin applications have been focused primarily on food preservation, either alone or in combination with other compounds. The long shelf life of food products relies on adding chemicals, sugars, salts, and other preservatives allowed by the regulation. The addition of these substances reduces water activity, inhibiting the growth of undesirable pathogenic microorganisms that can spoil food. However, the addition of these chemicals benefits the industry but not the consumer since the continuous consumption of chemical preservatives through packaged foods can affect consumers’ health. There is an association of these additives with chronic degenerative diseases, and the intake of these additives can prompt the development of some types of cancer (Monteiro et al. 2010; Moubarac et al. 2013). A more friendly strategy to preserve food products is the use of bacteriocins beneficial for both the food industry and consumers, helping to reduce the use of chemical preservatives in food (Sarika et al. 2019). The growth of pathogens in food can be controlled by the inoculation of bacteriocin-producing lactic acid bacteria or by the addition of purified bacteriocins (Silva et al. 2018). Bacteriocins have also been added to the coating of food packaging to reduce food spoilage (Salgado et al. 2015; Castellano et al. 2017).
The use of bacteriocins as food preservatives does not affect the organoleptic properties of foods. There are safe bacteriocins for human consumption, such as Enterocin AS-48 (Sánchez-Hidalgo et al. 2011), lacticin 3147 (Mills et al. 2017), and salmocins (Schneider et al. 2018) but only nisin (NisaplinTM, BiosafeTM), pediocin PA-1 (MicrogardTM, Alta 2431), sakacin (BactofermTM B-2, BactofermTM B-FM) and leucocin A (BactofermTM B-SF-43) are commercially used to improve shelf-life of food (Vijay Simha et al. 2012; Daba and Elkhateeb 2020).
The Food and Agriculture Organization (FAO) support the use of probiotics in food systems, since probiotics offer health benefits, especially for the gastrointestinal tract. Probiotics play an important role in modifying some metabolic pathways that, in turn, regulate cell proliferation, apoptosis, differentiation, angiogenesis, inflammation, and metastasis, which are relevant aspects to prevent the development of cancer (Bermudez-Brito et al. 2012).
Bacteriocins have shown cytotoxic activity against cancer cells, and therefore they could be considered tools to develop new anticancer drugs (Baindara et al. 2018). The charge of normal cell membranes is neutral, while cancer cells have a negative charge due to the high content of anionic phosphatidylserine, o-glycosylated mucins, sialylated gangliosides, and heparin sulfates. Bacteriocins, being cationic peptides, can preferentially bind to the negatively charged membrane of cancer cells compared to normal cells. Some bacteriocins with anticancer activities are colicins, which have shown cytotoxic activity against various human tumor cell lines such as breast cancer, colon cancer, and bone cancer (Kaur and Kaur 2015). Some examples of the potential applications of bacteriocins are shown in Table I.
Bacteriocins with potential application as therapeutic and food preservatives.
Bacteriocin | Producer bacteria | Target microorganism | Use | Reference |
---|---|---|---|---|
AMA-K, Leucocin K7 | Amasi, fermented milk product | (Todorov 2008) | ||
Aureocin A70 | Dairy product | (Carlin Fagundes et al. 2016) | ||
Bacteriocin 32Y | Pork and beef | (Gálvez et al. 2007) | ||
Bacteriocin GP1 | Fish | (Sarika et al. 2019) | ||
Bovicin HC5 + Nisin | Fresh cheese | (Pimentel-Filho et al. 2014) | ||
Divergicin M35 | Smoked fish | (Benabbou et al. 2020) | ||
Enterocin | Feta cheese | (Sarantinopoulos et al. 2002) | ||
Enterocin 416K1 | Cottage cheese | (Iseppi et al. 2008) | ||
Enterocin AS-48 | Cheese, vegetable, purees, and soups | (Gálvez et al. 2007) | ||
H1, H2, H3, H4 | Antimicrobial used in fish | (Feliatra et al. 2018) | ||
Lacticin 3147 | Matured and cottage cheese | (Mills et al. 2017) | ||
Lacticin NK24 | Seafood | (Lee and Paik 2001) | ||
Leucocin K7 | L. mesenteroides K7 | Dairy product | (Shi et al. 2016) | |
Mecedocin | Kasseri cheese | (Anastasiou et al. 2009) | ||
NE | Semi-mature cheese | (Bogovič Matijašić et al. 2007) | ||
Nisin | Dairy products, meat, seafood | (Juturu and Wu 2018) | ||
Pediocin PA1 | Dairy products, meat | (Liu et al. 2008) | ||
Plant-made salmocins | Red meat | (Schneider et al. 2018) | ||
Plant-made colicins (GRN 676, GRN 593) | Meat, fruits, or vegetables | (Hahn-Löbmann et al. 2019) | ||
Psicolin 126, carnocyclin A | Ready-to-eat meat products | (Liu et al. 2014) | ||
Reuterin | Food preservation | (Helal et al. 2016) | ||
Sakacin P | Beef and Salmon | (Teneva-Angelova et al. 2018) | ||
Thuricin | B. thuringiensis | Food preservation and disease associate to | (Huang et al. 2016) | |
ABP118 | Antimicrobial agent | (Riboulet-Bisson et al. 2012) | ||
Colicins Js and Z | Gastrointestinal infections | Bosák et al. 2021 | ||
Divercin V41 | Antimicrobial agent | (Rihakova et al. 2010) | ||
Duramycin | Antimicrobial, anti-viral, immunomodulation, ion channel modulation, treatment of atherosclerosis and cystic fibrosis | (Huo et al. 2017) | ||
Enterocin CRL35 | Gastrointestinal infections | (Salvucci et al. 2012) | ||
Epidermin and mersacidin-like peptides | Acne, folliculitis. | (Gillor et al. 2008) | ||
Gallidermin/epidermin | Skin infections or associated with implants and prostheses | (Bengtsson et al. 2018; Bonelli et al. 2006) | ||
Gassericin E | Pathogens associated with vaginosis | Vaginal infections | (Maldonado-Barragán et al. 2016) | |
Haemocin type B | Respiratory infections | (Latham et al. 2017) | ||
Lactocin 160 | Urogenital tract infections, bacterial vaginosis | (Turovskiy et al. 2009) | ||
Laterosporulin10 | Human microbial pathogens | (Baindara et al. 2016) | ||
Mersacidin | Methicillin-resistant | Skin infection | (Kruszewska et al. 2004) | |
Microcin J25 (lasso-peptide) | Gastrointestinal infections | (Dobson et al. 2012) | ||
Nisin A, Nisin Z, Nisaplin | Gastrointestinal, respiratory, and skin infections, oral health | (Shin et al. 2016) | ||
Oralpeace TM (encapsulated nisin) | Dental caries, gingivitis | (Perez et al. 2014) | ||
Piscicolin 126 | Antimicrobial agent | (Miller and McMullen 2014) | ||
Plantaricin 423 | Antimicrobial agent | (Guralp et al. 2013) | ||
PLNC8 αβ | Antimicrobial agent | (Bengtsson et al. 2020) | ||
R-pyocins | Antimicrobial agent | (Redero et al. 2018) | ||
TOMM Streptolysin S (SLS) | Hemolytic and cytotoxic activity against macrophages and neutrophils | (Molloy et al. 2015) | ||
Cancer cell lines | ||||
Azurin | MCF-7, UISO-Mel-2, osteosarcoma (U2OS) | (Nguyen and Nguyen 2016) | ||
Bovicin HC5 | MCF-7, HepG2 | (Rodrigues et al. 2019) | ||
Colicin E3 | P388, HeLa, HS913T | (Kohoutova et al. 2014 | ||
Duramycin | AsPC-1, Caco-2, Colo320, CT116, JJN3, Lovo, MCF-7, MDA-B-231, MIA PaCa-2 | (Rodrigues et al. 2019) | ||
Enterocin LNS18 | HepG2 | (Al-Madboly et al. 2020) | ||
Laterosporulin LS10 | HeLa, MCF-7, H1299, HEK293T, HT1080 | (Baindara et al. 2016) | ||
M2163, M2386 | SW480 | (Rodrigues et al. 2019) | ||
Microcin E492 | HeLa, Burkitt lymphoma variant (RJ2.25) | (Kaur and Kaur 2015) | ||
Nisin A | Head and neck squamous cell carcinoma (HNSCC) | (Shin et al. 2016) | ||
Pediocin K2a2-3 | HT2a, HeLa | (Villarante et al. 2011) | ||
Pediocin CP2 | HeLa, MCF-7, HepG2, murine myeloma (Sp2/0-Ag 14) | (Kumar et al. 2012) | ||
Pep27anal2 | Jurkat, HL-60, AML-2, MCF-7, SNU-601 | (Rodrigues et al. 2019) | ||
Plantaricin A | GH4, Reh, Jurkat, PC12, N2A | (Sand et al. 2013) | ||
Plantaricin P1053 | E705 | (De Giani et al. 2019) | ||
Pyocin S2 | HepG2, Im9, murine tumor (mKS-A TU-7), human fetal foreskin fibroblast (HFFF) | (Abdi-Ali et al. 2004) | ||
Sungsanpin | A549 | (Um et al. 2013) | ||
Smegmatocin | HeLa, AS-II, HGC-27, mKS-A TU-7 | (Kaur and Kaur 2015) |
NE – non specified
The potential therapeutic uses of bacteriocins produced by lactic acid bacteria have increased over time. López-Cuellar et al. (2016) found that 37% of the investigations on bacteriocins were focused on medical applications including cancer, systemic infections, stomatology, skincare, and contraceptives. 29% of studies focused on food preservation, 25% on bio-nanomaterials, and 9% within veterinary. The number of patents on bacteriocins has also increased. From 2004 to 2015, 245 bacteriocin patents were issued, 31% related to the biomedical field, 29% to food preservation, 5% to veterinary medicine, 13% to production and purification process, and 16% to molecular modifications in producer strains. The smallest proportion concerns bio-nanomaterials and industrial applications.
The indiscriminate use of agrochemicals has caused severe damage to human health and the environment. This problem aims to find alternatives to fight pests and diseases in a more environmentally friendly way. Bacteria that produce inhibitory substances have been used as inoculants to indirectly stimulate the growth of crops, fighting the phytopathogens. Plant growth-promoting rhizobacteria (PGPR) are generally marketed in the form of mono or multi-inoculants that include bacteria such as
Some examples of bacteriocins applied to agriculture are agrocin 84 and thuricin 17. Agrocin 84 is produced by
Biocontrol potential of bacteriocin-producing microorganisms in agriculture.
Bacteriocin | Producer bacterium | Phytopathogen | Reference |
---|---|---|---|
Amylocyclin | (Scholz et al. 2014) | ||
Bacteriocin 32Y | (Sindhu et al. 2016) | ||
Carocin D | (Grinter et al. 2012; Roh et al. 2010) | ||
Enterocin UNAD 046 | (David and Onifade, 2018) | ||
Fluoricin BC8 | (Sindhu et al. 2016) | ||
Gluconacin | (Oliveira et al. 2018) | ||
LlpA | (Parret et al. 2005) | ||
Morricin 269, Kurstacin 287, Kenyacin 404, Entomocin 420, Tolworthcin 524 | (De La Fuente-Salcido et al. 2008; Salazar-Marroquín et al. 2016) | ||
NE | (Lavermicocca et al. 2002) | ||
BLIS RC-2 | (Abriouel et al. 2011) | ||
NE | (Marín-Cevada et al. 2012) | ||
BL8 | (Subramanian and Smith 2015) | ||
Plantazolicin | (Chowdhury et al. 2015) | ||
Putidacin L1 | (Rooney et al. 2020) | ||
Rhizobiocin | (Kaur Maan and Garcha 2018) | ||
SF4c tailocins | (Príncipe et al. 2018) | ||
Syringacin M | (Li et al. 2020) |
NE – non specified
The autochthonous bacteria that colonize the entire human gastrointestinal tract, from the mouth to the colon, confer various physiologic benefits to the host. The prokaryotic symbiont population in humans ranges from 103–105 CFU/ml in the jejunal lumen) of healthy individuals to 1011–1012 CFU/ml in the colon, gut microbiota, prevents pathogen growth in the gastrointestinal tract (Sundin et al. 2017). This regulation is given through various microbial mechanisms, one of them is the release of bacteriocins, which prevent dysbiosis and consolidate the homeostasis of the gastrointestinal microbiota. The homeostatic balance in the human gut microbiota has become a significant public health problem due to changes in eating habits, type of diet, and administration of broad-spectrum antibiotics (Cotter et al. 2013). Ultra-processed food intake has increased saturated fats, omega-6 fatty acids, trans-fatty acids, and simple carbohydrates in the human diet while it has decreased the intake of omega-3 fatty acids, fiber, and complex carbohydrates. This diet high in fat and carbohydrates and low in micronutrients can disturb the human microbiota with concomitant metabolic disorders (Miclotte and Van de Wiele 2020).
Probiotics can colonize, at least temporally, the human gastrointestinal tract due to the efficient competition mediate by bacteriocin production. Thus, the intake of
In some cases, the growth rate of a resistant population can be higher than that of the bacteriocin-producing population (P), which generally possess a plasmid with genes encoding the bacteriocin and bacteriocin-specific immunity protein that make the bacteriocin-producing population immune to its bacteriocin. Still, at the same time, the resistant population (R) has a slower growth rate than that of the sensitive population (S). The susceptible population has an advantage over the resistant population because sensitive bacteria have a higher growth rate. The resistant population has an advantage over the bacteriocin-producing population because of its higher growth rate. And the bacteriocin-producing population can displace susceptible populations because bacteriocin-producing bacteria can kill sensitive bacteria making the three types of bacterial populations coexist in a balance of subpopulations preserving the diversity of the community (Kerr et al. 2002).
The bioinformatic analysis of bacteriocins encoded within 317 microbial genomes found in the human intestine revealed 175 bacteriocins in Firmicutes (which includes LAB), 79 in Proteobacteria, 34 in Bacteroidetes, and 25 in Actinobacteria (Drissi et al. 2015). The analysis showed that bacteriocins produced by the intestinal bacteria display wide differences, in the size and amino acid composition, compared to other bacteriocins. These bacteriocins contain less aspartic acid, leucine, arginine, and glutamic acid but more lysine and methionine. Depending on their α-helical structure, charge, and hydrophobicity, they may have a broader spectrum of activity (Zelezetsky and Tossi 2006) but, in turn, lower antimicrobial activity and, therefore, they can better modulate microbial populations (Drissi et al. 2015). The microbial community that inhabits the human gut appears to impart specific functions to human metabolism and health by interconnecting signals from the brain, the immune system, the endocrine system, and the gut microbiota itself (Vivarelli et al. 2019). So, depending on the type of bacteria colonizing the gastrointestinal tract will determine the type of signaling molecules released and, therefore, the impact on host health and disease. That is why the microbial diversity of microbiota is tightly regulated. An example of this type of regulation exerted by bacteriocins is the effect of plantaricin P1053 produced by
A multidrug-resistant
According to the World Intellectual Property Organization (WIPO), over the last 30 years, more than 800 patent applications with the term “bacteriocin” in title or abstract were published, while Espacenet website reports more than 8900. Fig. 4 shows the patents published between January 1, 2000, and August 7, 2020, using the Patent Inspiration search engine with the term “bacteriocin”. Over the last 20 years, China has published 234 patents, followed by the United States with 132, while Mexico only published 17 patents (Fig. 4). Among these patents, 312 (36.4%) are associated with nisin and lactic acid bacteria.
Bacteriocins have fascinating properties concerning their size, structure, mechanism of action, inhibitory spectrum, and immunity mechanisms that endorse them with market potential. However, just four bacteriocin formulations are commercially available: nisin (NisaplinTM, BiosafeTM, OralpeaceTM), pediocin PA-1 (MicrogardTM, Alta 2341), sakacin (BactofermTM B-2, BactofermTM B-FM) and leucocin A (BactofermTM B-SF-43) are mainly used as food preservatives in the United States and Canada (Daba and Elkhateeb 2020; Radaic et al. 2020). Other FDA-approved bacteriocins, with the intended use as an antibacterial for food, are colicins, salmocins, and
Bacteriocin formulations can be used as nutritional supplementation. Few
Compared to the food industry, the medical field could represent a higher profit for the use of bacteriocins. However, to exploit the full potential of bacteriocins in the medical industry, they must overcome some drawbacks such as sensitivity to proteases, immunogenicity issues, and the development of bacteriocin resistance by pathogenic bacteria. In this regard, advanced chemical approaches can be used to make disulfide bridges, head-to-tail macrocyclization, N-terminus formylation, amino acid substitutions, and other modifications; to make bacteriocins more potent and stable, enabling them to surpass their current drawbacks (Bédard and Biron 2018). Another factor that prevents the commercial use of bacteriocins in medical applications might be attributed to the low approval of the regulatory process. Over the last decade, the number of
Bacteriocins have become an attractive tool to preserve food and improve human health. Bacteriocins can eliminate specific pathogen microorganisms while favoring the preservation of other populations. Since the impact of bacteriocins on each microbial community is not well understood yet, there are limitations to exploit all their potential. It is necessary to continue performing rigorous research focused on developing antimicrobials, anticancer agents, and microbiota modulators before bacteriocins can be available to consumers.