Characterization of two antimicrobial peptides produced by a halotolerant Bacillus subtilis strain SK.DU.4 isolated from a rhizosphere soil sample

Abstract

A bacterial strain producing two antimicrobial peptides was isolated from a rhizosphere soil sample and identified as Bacillus subtilis based on both phenotypic and 16S rRNA gene sequence phylogenetic analysis. It grew optimally up to 14% NaCl and produced antimicrobial peptide within 24 h of growth. The peptides were purified using a combination of chemical extraction and chromatographic techniques. The MALDI-TOF analysis of HPLC purified fractions revealed that the strain SK.DU.4 secreted a bacteriocin-like peptide with molecular mass of 5323.9 Da and a surface-active lipopeptide (m/z 1056 Da). The peptide mass fingerprinting of low-molecular-weight bacteriocin exhibited significant similarity with stretches of secreted lipoprotein of Methylomicrobium album BG8 and displayed 70% sequence coverage. MALDI MS/MS analysis elucidated the lipopeptide as a cyclic lipopeptide with a β-hydroxy fatty acid linked to Ser of a peptide with seven α-amino acids (Asp-Tyr-Asn-Gln-Pro-Asn-Ser) and assigned it to iturin-like group of antimicrobial biosurfactants. However, it differed in amino acid composition with other members of the iturin family. Both peptides were active against Gram-positive bacteria, suggesting that they had an additive effect.

Isolation, screening and growth optimization of antagonistic Bacillus subtilis MS21 from Thengapattanam estuary against plant fungal pathogens

“…In the present study 1% NaCl supported maximum growth of B. subtilis MS21 (Fig.7), whereas Baindara et al, 2013 observed 14% NaCl as the optimum for the growth of halotolerant Bacillus subtilis strain SK.DU.4 isolated from a rhizosphere soil. Salinity requirement seemed to be based on the environment from which the strain was originated.…”

Laterosporulin10: a novel defensin like Class IId bacteriocin from Brevibacillus sp. strain SKDU10 with inhibitory activity against microbial pathogens

“…Peptide quantified between 0-16 µM concentration was used for further studies, including determination of minimum inhibitory concentration (MIC), molecular mass and N-terminal sequencing as mentioned below. This peptide was also used for an in-gel activity assay against S. aureus MTCC 1430 as described above (Baindara et al, 2013).…”

Characterization of the Antimicrobial Peptide Penisin, a Class Ia Novel Lantibiotic from Paenibacillus sp. Strain A3

“…However, the concentration was confirmed based on the extinction coefficient, once we obtained the amino acid sequence of the peptide. Test strains were grown to logarithmic phase (between 0.3 to 0.4 optical density units) under optimal conditions and used for assays performed in triplicate, as described earlier (27).…”