Antimicrobial Activity of Bacillus amyloliquefaciens ANT1 Toward Pathogenic Bacteria and Mold: Effects on Biofilm Formation

Metabolomic Insights of Biosurfactant Activity from Bacillus niabensis against Planktonic Cells and Biofilm of Pseudomonas stutzeri Involved in Marine Biofouling

In marine environments, biofilm can cause negative impacts, including the biofouling process. In the search for new non-toxic formulations that inhibit biofilm, biosurfactants (BS) produced by the genus Bacillus have demonstrated considerable potential. To elucidate the changes that BS from B. niabensis promote in growth inhibition and biofilm formation, this research performed a nuclear magnetic resonance (NMR) metabolomic profile analysis to compare the metabolic differences between planktonic cells and biofilms of Pseudomonas stutzeri, a pioneer fouling bacteria. The multivariate analysis showed a clear separation between groups with a higher concentration of metabolites in the biofilm than in planktonic cells of P. stutzeri. When planktonic and biofilm stages were treated with BS, some differences were found among them. In planktonic cells, the addition of BS had a minor effect on growth inhibition, but at a metabolic level, NADP+, trehalose, acetone, glucose, and betaine were up-regulated in response to osmotic stress. When the biofilm was treated with the BS, a clear inhibition was observed and metabolites such as glucose, acetic acid, histidine, lactic acid, phenylalanine, uracil, and NADP+ were also up-regulated, while trehalose and histamine were down-regulated in response to the antibacterial effect of the BS.

Antimicrobial Bacillus: Metabolites and Their Mode of Action

The agricultural industry utilizes antibiotic growth promoters to promote livestock growth and health. However, the World Health Organization has raised concerns over the ongoing spread of antibiotic resistance transmission in the populace, leading to its subsequent ban in several countries, especially in the European Union. These restrictions have translated into an increase in pathogenic outbreaks in the agricultural industry, highlighting the need for an economically viable, non-toxic, and renewable alternative to antibiotics in livestock. Probiotics inhibit pathogen growth, promote a beneficial microbiota, regulate the immune response of its host, enhance feed conversion to nutrients, and form biofilms that block further infection. Commonly used lactic acid bacteria probiotics are vulnerable to the harsh conditions of the upper gastrointestinal system, leading to novel research using spore-forming bacteria from the genus Bacillus. However, the exact mechanisms behind Bacillus probiotics remain unexplored. This review tackles this issue, by reporting antimicrobial compounds produced from Bacillus strains, their proposed mechanisms of action, and any gaps in the mechanism studies of these compounds. Lastly, this paper explores omics approaches to clarify the mechanisms behind Bacillus probiotics.

Antagonistic Activity of Antimicrobial Metabolites Produced from Seaweed-Associated Bacillus amyloliquefaciens MTCC 10456 Against Malassezia spp

Members of the genus Malassezia are known to be opportunistic pathogens responsible for causing skin disorders such as seborrheic dermatitis or dandruff, pityriasis versicolor, folliculitis, atopic dermatitis, and psoriasis. Due to the side effects caused by prolonged use of current topical antifungal agents, development of an alternative treatment is necessary. Fermentative production of antimicrobial metabolites from Bacillus amyloliquefaciens MTCC 10456 was carried out, and their antagonistic activity against Malassezia furfur and Malassezia globosa was evaluated. The antifungal metabolites were isolated by acid precipitation, and bioassay-guided simultaneous separation of the antimicrobial compounds was done by reversed-phase high-performance liquid chromatography (RP-HPLC). The fraction which demonstrated antifungal activity consisted of bacilysin, homologues of bacillomycin D, and members of the macrolactin family. The presence of bacilysin was detected using specific inhibitor assays and homologues of bacillomycin D, and macrolactins were identified using liquid chromatography/high-resolution electrospray ionization-mass spectrometry (LC/HRESI-MS/MS) analysis. Synergism among the identified compounds was observed which enhanced the antagonistic activity against Malassezia spp. To our knowledge, this is the first study to report the co-production and separation of members of macrolactin antibiotics, lipopeptides such as bacillomycin D and dipeptide antibiotic bacilysin, by any Bacillus strain from marine environment. Activity of individual compounds against Malassezia has been reported which may facilitate their application in the field of dermatology and in cosmetic products.

Bacillaenes: Decomposition Trigger Point and Biofilm Enhancement in Bacillus

Bacillaenes are a class of poly-unsaturated enamines produced by Bacillus strains that are notoriously unstable toward light, oxygen, and normal temperature. Herein, in an in-depth study of this highly unstable chemotype, the stability and biological function of bacillaenes were investigated. The structure change of the bacillaene scaffold was tracked by time-course 1H NMR data analysis coupled with the differential analysis of 2D-NMR spectra method, which was demonstrated to be a "domino" effect triggered by 4',5'-cis (2 and 3) configuration rearranged to trans (2a and 3a). These findings provide the possibility for stabilizing the bacillaene scaffold by chemical modification of its trigger points. In the biofilm assay, compounds 1 and 2 accelerated self-biofilm formation in Bacillus methylotrophicus B-9987 at low concentrations of 1.0 and 0.1 μg/mL. Interestingly, bacillaenes play dual roles as antibiotic and biofilm enhancers in a dose-dependent manner, both of which serve in the self-protection of Bacillus.

Synergistic Inhibitory Activity of Bacillomycin D, Surfactin and Nisin against Thermoascus crustaceus, Neosartorya hiratsukae and Bacillus subtilis, Responsible for Cardboard Spoilage

Corrugated cardboard boxes are one of the largest paper-based packaging forms used for shipping and handling of wide variety of products in different end-use industries due to low cost, low weight and recyclability. Due to its organic composition, they are highly susceptible to spoilage from heat-resistant microbial spores, leading to economic losses and health risks. In this study, the efficacy of lipopeptides produced from Bacillus amyloliquefaciens MTCC 10456 against thermotolerant Thermoascus crustaceus, Neosartorya hiratsukae and Bacillus subtilis, isolated from spoiled cardboard boxes, was investigated. Lipopeptides were isolated by salt-precipitation of fermentation broth and activity-guided Reverse Phase-High Performance Liquid Chromatography (RP-HPLC). Inhibitory fractions consisted of bacillomycin D and surfactin, which were identified using liquid chromatography-electrospray ionization mass spectrometry (LC-ESI-MS/MS) analysis. Mixture of lipopeptides with nisin (3:2 w/w) asserted significant synergistic effect on the tested pathogens which reduced the minimum inhibitory concentrations (MIC) values and increased their inhibition spectra. Preservative coating containing lipopeptides and nisin was applied on the corrugated cardboard surfaces by mixing with starch-based additive by spread-coating method. It demonstrated biopreservative efficacy against the targeted microorganisms at during the observational period of 180 days. Reduction in microbial count of 4 log cycles was observed in 20 days and showed controlled release of coated peptides which indicate its suitability for packaging purposes. Findings from this study suggests an effective and scalable strategy to prevent microbial spoilage thereby extending the storage period of cardboard boxes.

Effects of CGA-N12 on the membrane structure of Candida tropicalis cells

The antimicrobial peptide CGA-N12 (NH2-ALQGAKERAHQQ-COOH) is an active peptide derived from chromogranin A (CGA) and consists of the 65th to 76th amino acids of the N-terminus. The results of our previous studies showed that CGA-N12 exerts anti-Candida activity by inducing apoptosis without destroying the integrity of cell membranes. In this study, the effect of CGA-N12 on the cell membrane structure of Candida tropicalis was investigated. CGA-N12 resulted in the dissipation of the membrane potential, the increase in membrane fluidity, and the outflow of potassium ions in C. tropicalis without significantly changing the ergosterol level. Fluorescence quenching was applied to evaluate the membrane channel characteristics induced by CGA-N12 through detection of the following: membrane permeability of hydrated Cl− (ϕ ≈ 0.66 nm) using the membrane-impermeable halogen anion-selective fluorescent dye lucigenin, passage of the membrane-impermeable dye carboxyfluorescein (CF) (ϕ ≈ 1 nm) through the membrane, and membrane permeation of H3O+ based on the membrane non-permeable pH-sensitive fluorescent dye 8-hydroxypyrene-1,3,6-trisulfonic acid, trisodium salt (HPTS). In conclusion, CGA-N12 can induce the formation of non-selective ion channels <1 nm in diameter in the membranes of C. tropicalis, resulting in the leakage of potassium ions, chloride ions, and protons, among others, leading to dissipation of the membrane potential. As a result, the fluidity of membranes is increased without destroying the synthesis of ergosterol is not affected.

The lipopeptide 6-2 produced by Bacillus amyloliquefaciens anti-CA has potent activity against the biofilm-forming organisms

Both the whole cells and protoplasts of Pseudomonas aeruginosa PAO1 and Bacillus cereus, two biofilm-forming bacteria, were disrupted by the lipopeptide 6-2 produced by Bacillus amyloliquefaciens anti-CA. The lipopeptide 6-2 could also effectively inhibit the formation of biofilms and disperse pre-formed biofilms. Live/dead staining of the biofilms grown in the absence or presence of the lipopeptide 6-2 showed that more dead bacterial cells in the presence of the lipopeptide than those in the absence of the lipopeptide and biofilm formation was greatly reduced by the lipopeptide 6-2. Expression of the PslC gene related to exopolysaccharides in P. aeruginosa PAO1 was also inhibited. All these results demonstrated that the lipopeptide 6-2 produced by B. amyloliquefaciens anti-CA had a high activity against biofilm-forming bacteria. The lipopeptide 6-2 also killed the larvae of Balanus amphitrite and inhibit the germination of Laminaria japonica spore and growth of protozoa, all of which were the fouling organisms in marine environments.