Broad spectrum antimicrobial activities from spore-forming bacteria isolated from the Vietnam Sea

Heterologously expressed SacP23, a novel bacteriocin from Paenibacillus polymyxa #23, is active against methicillin resistant Staphylococcus aureus

Antimicrobial peptides have the potential to be used in a range of applications, including as an alternative to conventional antibiotics for the treatment of bacterial infections of humans and animals. Therefore, there is interest in identifying novel bacteriocins which have desirable physico-chemical properties or antimicrobial activities. Paenibacillus polymyxa #23, isolated from a marine sponge, has wide spectrum antimicrobial activity against Gram-negative and Gram-positive bacteria. To explore the basis of this antimicrobial activity, the complete genome sequence of the strain was examined. Multiple genes predicted to encode antimicrobial peptides were identified. One gene was predicted to encode a novel sactipeptide bacteriocin, named SacP23. To confirm that SacP23 does have antimicrobial activity and to explore the antimicrobial spectrum of the peptide it was heterologously expressed in Bacillus subtilis. A cluster of eight genes, encoding a full complement of accessory genes as well as the structural gene expressed from the native promoter, was cloned into B. subtilis BS54A. The recombinant strain displayed antimicrobial activity against several Gram-positive bacteria, including multi-drug resistant Staphylococcus aureus. Heterologous expression of a whole gene cluster offers a powerful way to interrogate and resolve the various antimicrobial activities expressed by native strains that encode multiple compounds of interest.

Identification of a New Compound (4-Fluoro-2-Trifluoromethyl Imidazole) Extracted from a New Halophilic Bacillus aquimaris Strain Persiangulf TA2 Isolated from the Northern Persian Gulf with Broad-Spectrum Antimicrobial Effect

Background

The unique ecosystem of the Persian Gulf has made it a rich source of natural antimicrobial compounds produced by various microorganisms, especially bacteria, which can be used in the treatment of infectious diseases, especially those of drug-resistant microbes.

Objectives

This study aimed to identify antimicrobial compounds in the bacteria isolated from the northern region of the Persian Gulf in Abadan (Chavibdeh port), Iran, for the first time.

Materials and Methods

Sampling was performed in the fall on November 15, 2019, from 10 different stations (water and sediment samples). The secondary metabolites of all isolates were extracted, and their antimicrobial effects were investigated. 16S ribosomal ribonucleic acid sequencing was used for the identification of the strains that showed the best inhibition against selected pathogens, and growth conditions were optimized for them. A fermentation medium in a volume of 5000 mL was prepared to produce the antimicrobial compound by the superior strain. The extracted antimicrobial compounds were identified using the gas chromatography-mass spectrometry technique. Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were determined for the superior strain. The effects of salinity, pH, and temperature on the production of antimicrobial compounds were determined by measuring the inhibitory region (mm) of methicillin-resistant Staphylococcus aureus (MRSA).

Results

Four new strains with antimicrobial properties (i.e., Halomonas sp. strain Persiangulf TA1, Bacillus aquimaris strain Persiangulf TA2, Salinicoccus roseus strain Persiangulf TA4, and Exiguobacterium profundum strain Persiangulf TA9) were identified. The optimum growth temperatures were determined at 37-30, 37, and 40 °C for TA1 and TA2, TA4, and TA9 strains, respectively. The optimum pH values for the four strains were 7, 6-7, 7.5, and 6.5-7.5, respectively. The optimal salt concentrations for the four strains were 15%, 2.5-5%, 7.5%, and 5%, respectively. The ethyl acetate extract of strain Persiangulf TA2 showed extensive antimicrobial activity against human pathogens (75%) and MRSA. The most abundant compound identified in TA2 extract was the new compound 4-fluoro-2-trifluoromethyl imidazole. The MBC and MIC for the ethyl acetate extract of strain TA2 were 20 and 5 mg. mL-1 (Staphylococcus aureus), 40 and 20 mg. mL-1 (MRSA, Escherichia coli, and Enterococcus faecalis), 40 and 10 mg. mL-1 Acinetobacter baumannii), and 80 and 40 mg. mL-1 (Staphylococcus epidermidis, Shigella sp., Bacillus cereus, and Klebsiella pneumoniae), respectively. The optimal conditions for antibiotic production by TA2 strain were 5% salt concentration, pH of 7, and temperature of 35 °C.

Conclusion

Newly detected natural compounds in TA2 strain due to superior antimicrobial activity even against MRSA strain can be clinically valuable in pharmacy and treatment.

Molecular Identification and Characterization of Probiotic Bacillus Species with the Ability to Control Vibrio spp. in Wild Fish Intestines and Sponges from the Vietnam Sea

Vibriosis in farmed animals is a serious threat to aquaculture worldwide. Using probiotics and anti-Vibrio antimicrobial substances in aquaculture systems can be a means of preventing Vibrio infections. Therefore, we aimed to characterize and compare 16 potential anti-Vibrio probiotics (Vi+) isolated from marine sponges and fish intestines collected from the Vietnam Sea, as well as an anti-Vibrio bacteriocin to fully explore their application potentials. 16S rRNA sequencing confirmed all Vi+ to be Bacillus species with different strain variants across two sample types. An obvious antimicrobial spectrum toward Gram-negative bacteria was observed from intestinal Vi+ compared to sponge-associated Vi+. The reason was the higher gene frequency of two antimicrobial compounds, non-ribosomal peptides (NRPS) and polyketide type-I (PKS-I) from intestinal Vi+ (66.7%) than sponge-associated Vi+ (14.3% and 0%, respectively). Additionally, a three-step procedure was performed to purify an anti-Vibrio bacteriocin produced by B. methylotrophicus NTBD1, including (i) solvent extraction of bacteriocin from cells, (ii) hydrophobic interaction chromatography, and (iii) reverse-phase HPLC. The bacteriocin had a molecular weight of ~2-5 kDa, was sensitive to proteolysis and thermally stable, and showed a broad antimicrobial spectrum, all of which are essential properties for promising feed additives. This study provides necessary information of the potential of probiotic Bacillus species with anti-Vibrio antimicrobial properties to study their further use in sustainable aquaculture.