Purification and characterization of a peptide from Bacillus licheniformis showing dual antimicrobial and emulsifying activities

Bacillus licheniformis: A Producer of Antimicrobial Substances, including Antimycobacterials, Which Are Feasible for Medical Applications

Bacillus licheniformis produces several classes of antimicrobial substances, including bacteriocins, which are peptides or proteins with different structural composition and molecular mass: ribosomally synthesized by bacteria (1.4-20 kDa), non-ribosomally synthesized peptides and cyclic lipopeptides (0.8-42 kDa) and exopolysaccharides (>1000 kDa). Different bacteriocins act against Gram-positive or Gram-negative bacteria, fungal pathogens and amoeba cells. The main mechanisms of bacteriocin lytic activity include interaction of peptides with membranes of target cells resulting in structural alterations, pore-forming, and inhibition of cell wall biosynthesis. DNase and RNase activity for some bacteriocines are also postulated. Non-ribosomal peptides are synthesized by special non-ribosomal multimodular peptide synthetases and contain unnatural amino acids or fatty acids. Their harmful effect is due to their ability to form pores in biological membranes, destabilize lipid packaging, and disrupt the peptidoglycan layer. Lipopeptides, as biosurfactants, are able to destroy bacterial biofilms. Secreted polysaccharides are high molecular weight compounds, composed of repeated units of sugar moieties attached to a carrier lipid. Their antagonistic action was revealed in relation to bacteria, viruses, and fungi. Exopolysaccharides also inhibit the formation of biofilms by pathogenic bacteria and prevent their colonization on various surfaces. However, mechanism of the harmful effect for many secreted antibacterial substances remains unknown. The antimicrobial activity for most substances has been studied in vitro only, but some substances have been characterized in vivo and they have found practical applications in medicine and veterinary. The cyclic lipopeptides that have surfactant properties are used in some industries. In this review, special attention is paid to the antimycobacterials produced by B. licheniformis as a possible approach to combat multidrug-resistant and latent tuberculosis. In particular, licheniformins and bacitracins have shown strong antimycobacterial activity. However, the medical application of some antibacterials with promising in vitro antimycobacterial activity has been limited by their toxicity to animals and humans. As such, similar to the enhancement in the antimycobacterial activity of natural bacteriocins achieved using genetic engineering, the reduction in toxicity using the same approach appears feasible. The unique capability of B. licheniformis to synthesize and produce a range of different antibacterial compounds means that this organism can act as a natural universal vehicle for antibiotic substances in the form of probiotic cultures and strains to combat various types of pathogens, including mycobacteria.

Mechanisms and the role of probiotic Bacillus in mitigating fish pathogens in aquaculture

Diseases are natural components of the environment, and many have economic implications for aquaculture and fisheries. Aquaculture is a fast-growing industry with the aim to meet the high protein demand of the ever-increasing global population; however, the emergence of diseases is a major setback to the industry. Probiotics emerged as a better solution to curb the disease problem in aquaculture among many alternatives. Probiotic Bacillus has been proven to better combat a wide range of fish pathogens relative to other probiotics in aquaculture; therefore, understanding the various mechanisms used by Bacillus in combating diseases will help improve their mode of action hence yielding better results in their combat against pathogens in the aquaculture industry. Thus, an overview of the mechanisms (production of bacteriocins, suppression of virulence gene expression, competition for adhesion sites, production of lytic enzymes, production of antibiotics, immunostimulation, competition for nutrients and energy, and production of organic acids) used by Bacillus probiotics in mitigating fish pathogens ranging from Aeromonas, Vibrio, Streptococcus, Yersinia, Pseudomonas, Clostridium, Acinetobacter, Edwardsiella, Flavobacterium, white spot syndrome virus, and infectious hypodermal and hematopoietic necrosis virus proven to be mitigated by Bacillus have been provided.

Antibacterial substances produced by pathogen inhibitory gut bacteria in Labeo rohita: Physico-chemical characterization, purification and identification through MALDI-TOF mass spectrometry

Application of antibiotics to combat bacterial diseases in fish has been criticized due to likely emergence of drug resistance. Therefore, investigation of new bioactive compounds from natural sources has been taken into account. This study was designed to purify and characterize the bioactive compound in the cell free supernatant (CFSs) of autochthonous gut bacteria (Bacillus methylotrophicus KU556164, B. amyloliquefaciens KU556165, Pseudomonas fluorescens KU556166 and B. licheniformis KU556167) isolated from rohu, Labeo rohita. CFSs were antagonistic to fish pathogenic Aeromonas spp., moderately thermo-tolerant and active in wide range of pH (5-11). Antibacterial activity of the CFSs was reduced by the action of proteases (e.g., Proteinase K and Trypsin), indicating proteinaceous nature of the bioactive compound like the bacteriocins. Three-step purification procedure resulted in recovery of 16.97%, 18.04%, 33.33% and 6.38% activity of the antimicrobial protein produced by B. methylotrophicus, B. amyloliquefaciens, P. fluorescens and B. licheniformis, respectively. Purification at each step revealed decrease in protein content with gradual increase in the specific activity of the antimicrobial protein. The purified antibacterial compound ranged between 18.2 and 25.6 kDa. Identification through MALDI-TOF MS/MS and database search through Mascot search engine predicted that the bactericidal compound belonged to either alkaline proteases, or, transcriptional regulator and some hypothetical proteins. Apart from potential technological application of the antibacterial compound, the present study might show promise for application of gut-associated bacteriocinogenic bacteria to control diseases in fish caused by pathogenic bacteria.

Glycin-rich antimicrobial peptide YD1 from B. amyloliquefaciens, induced morphological alteration in and showed affinity for plasmid DNA of E. coli

Antimicrobial peptides (AMPs), low-molecular-weight proteins with broad-spectrum antimicrobial activity, are the most promising candidates for the development of novel antimicrobials. A powerful cationic glycine-rich AMP YD1 (MW ~ 1.0 kDa) was purified from Bacillus amyloliquefaciens CBSYD1 isolated from traditional Korean fermented food kimchi, for the treatment of multidrug-resistant (MDR) bacteria. Strain CBSYD1 was identified 99.79% similar to Bacillus amyloliquefaciens subsp. plantarum FZB42(T) by 16S rRNA sequence analysis. The amino acid sequence residues of YD1 were determined to be Ala-Pro-Lys-Gly-Val-Gln-Gly-Pro-Asn-Gly by Edman degradation method. After the analysis and comparison of YD1 peptide sequence using several bioinformatic servers, peptide sequence has been considered to be unique. YD1 displayed antimicrobial activity against gram-positive and gram-negative bacteria. The minimal inhibitory concentrations (MIC) of YD1 for Escherichia coli KCTC1923 (E. coli), methicillin-resistant Staphylococcus aureus B15 (MRSA), and vancomycin-resistant enterococci (VRE) ranged from 8 to 64 µg/mL, representing greater potency than commercial reference antibiotics. The antimicrobial mechanism of YD1 was determined to involve cell-penetrating translocation inside the cell and interaction with the DNA leading ultimately to bacterial cell death. Analogously, Gly-Pro-Asn-Gly is the likely expected cell-penetrating motif for YD1. YD1 could be a promising antimicrobial agent for the clinical application.

Investigation of the Antimicrobial Activity of Bacillus licheniformis Strains Isolated from Retail Powdered Infant Milk Formulae

This study investigated the potential antimicrobial activity of ten Bacillus licheniformis strains isolated from retail infant milk formulae against a range of indicator (Lactococcus lactis, Lactobacillus bulgaricus and Listeria innocua) and clinically relevant (Listeria monocytogenes, Staphylococcus aureus, Streptococcus agalactiae, Salmonella Typhimurium and Escherichia coli) microorganisms. Deferred antagonism assays confirmed that all B. licheniformis isolates show antimicrobial activity against the Gram-positive target organisms. PCR and matrix-assisted laser desorption ionization time-of-flight mass spectrometry analyses indicated that four of the B. licheniformis isolates produce the bacteriocin lichenicidin. The remaining six isolates demonstrated a higher antimicrobial potency than lichenicidin-producing strains. Further analyses identified a peptide of ~1,422 Da as the most likely bioactive responsible for the antibacterial activity of these six isolates. N-terminal sequencing of the ~1,422 Da peptide from one strain identified it as ILPEITXIFHD. This peptide shows a high homology to the non-ribosomal peptides bacitracin and subpeptin, known to be produced by Bacillus spp. Subsequent PCR analyses demonstrated that the six B. licheniformis isolates may harbor the genetic machinery needed for the synthesis of a non-ribosomal peptide synthetase similar to those involved in production of subpeptin and bacitracin, which suggests that the ~1,422 Da peptide might be a variant of subpeptin and bacitracin.

Physical chemical and biological characterization of a new bacteriocin produced by Bacillus cereus NS02

OBJECTIVE

To screen the bacteriocinogenic isolate from buffalo milk and to characterize it on physical, chemical and biological aspects for the application in biopreservation.

METHODS

Bacillus cereus (B. cereus) was isolated and assessed for its baceteriocinogenic activity. Bacteriocin was produced and purified by ammonium sulphate precipitation, dialysis and gel filtration chromatography. Purified bacteriocin was used to check its antimicrobial activity against food borne bacteria. Effect and stability of bacteriocin was determined with the respect to temperature, pH, enzymes, organic solvents and chemicals. Bacteriocin was also subjected to SDS PAGE analysis to determine its molecular weight. In addition, functional groups exist in the bacteriocin was determined by FTIR analysis.

RESULTS

B. cereus was identified by 16S rRNA sequence analysis. Bacteriocin showed increased activity against all the bacteria used and its activity unit was found to be 51, 200 AU/mL. It was stable to high temperature (100 °C) and wide range of pH (3-10), sensitive to proteolytic enzymes and resistant to nonproteolytic enzymes. It was low molecular weight (3.5 - 6 KDa) protein and FTIR study revealed the presence of amide group and NH stretching.

CONCLUSIONS

Bacteriocin produced in this study possesses the highest antimicrobial activity against both gram positive and gram negative bacteria thereby it has immense application as biopreservative agent. FTIR proved its peptide nature.

Characterization of an antimicrobial peptide produced by Bacillus subtilis subsp. spizezinii showing inhibitory activity towards Haemophilus parasuis

Haemophilus parasuis is the pathogen that causes Glässer's disease, a major illness affecting young pigs. The aim of this work was to investigate the antagonistic activity of antimicrobial substances produced by Bacillus species against H. parasuis. Among the tested strains, only Bacillus subtilis ATCC 6633 inhibited H. parasuis growth. The antibacterial substance was purified by ammonium sulfate precipitation, gel filtration chromatography on Sephadex G-50 and ion-exchange chromatography on DEAE-cellulose. The purification was about 100-fold with a yield of 0.33 %. The purified substance was resistant up to 80 °C and pH ranging 3-7, but the substance lost its activity when it was treated with proteases. The peptide had a molecular mass of 1083 Da and its sequence was determined by MS as NRWCFAGDD, which showed no homology with other known antimicrobial peptides. The complete inhibition of H. parasuis growth was observed at 20 µg peptide ml(-1) after 20 min of exposure. The peptide obtained by chemical synthesis also showed antimicrobial activity on H. parasuis. The identification of antimicrobial substances that can be effective against H. parasuis is very relevant to combat this pathogen that causes important losses in swine production.

A novel thermotolerant and acidotolerant peptide produced by a Bacillus strain newly isolated from a fermented food (kimchi) shows activity against multidrug-resistant bacteria

In an attempt to isolate effective antimicrobial peptides (AMPs) from a microbial source for the treatment of multidrug-resistant (MDR) bacteria, BCP61 was purified from Bacillus sp. CS61 newly isolated from the traditional fermented food kimchi. BCP61 (ca. 1100 Da) was purified to homogeneity using sequential chromatographic steps. It was found to be stable at pH 2.0-10.0 and up to 80 °C. BCP61 displayed antimicrobial activity against MDR bacteria such as meticillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant S. aureus (VRSA) and vancomycin-resistant enterococci (VRE). Minimal inhibitory concentrations of BCP61 for MRSA, VRSA and VRE were in the range 0.625-20μg/mL. The N-terminal amino acid sequence of BCP61 was A-I-N-X-D-A-A-Y-L, which differed from reported AMPs. The fourth unidentified amino acid was replaced and several peptides were synthesised. Among them, only cysteine replacement displayed antimicrobial activity. BCP61 from a food-borne strain may be useful in therapeutic applications.

Investigation of the cytotoxicity of antimicrobial peptide P40 on eukaryotic cells

The in vitro cytotoxicity of the antimicrobial peptide P40 was investigated. The food grade bacteriocin nisin was also analyzed for comparison. VERO cells were treated with different concentrations (0.02-2.5 microg ml(-1)) of nisin and P40, and cell viability and plasma membrane integrity were checked by MTT, neutral red uptake (NRU), and lactate dehydrogenase (LDH) assays. In MTT and NRU assays the EC(50) to the purified peptide P40 were 0.30 and 0.51 microg ml(-1), while values found to nisin were 0.35 and 0.79 microg ml(-1), respectively. In the LDH assay, the EC(50) was 0.57 and 0.62 microg ml(-1) for P40 and nisin, respectively. The peptide P40 revealed higher hemolytical activity (19%) when compared to nisin (4.9%) at the highest concentration tested (2.5 microg ml(-1)). Relatively few studies about the cytotoxicity of antimicrobial peptides are available. The determination of the cytotoxicity of antimicrobial peptides is an essential step to warrant their safe use.