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Open Access Highly Accessed Original article

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

Piyush Baindara1, Santi M Mandal2, Niharika Chawla1, Pradip Kumar Singh1, Anil Kumar Pinnaka1 and Suresh Korpole1*

Author Affiliations

1 MTCC and Gene Bank, CSIR-Institute of Microbial Technology, Sector 39A, Chandigarh, 160036, India

2 Central Research Facility, Indian Institute of Technology Kharagpur, Kharagpur, West Bengal, 721302, India

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AMB Express 2013, 3:2  doi:10.1186/2191-0855-3-2

Published: 5 January 2013

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.

Keywords:
Bacillus; Antimicrobial peptide; Lipopeptide; Chromatography; RP-HPLC; MALDI