Bioactive pyrrole-pyrazine derivative from a novel Bacillus species and review of the literature

Abstract

The rising antibiotic resistance is urging researchers to explore for new forms of antibiotics, notably from soil microorganisms such as Bacillus species. This study aimed to screen Bacillus strains from soil samples in Sudan for antifungal activity and to review relevant compounds from members of the genus in the literature. Out of 10 isolates from soil in Sudan, the strain JS6 (DSM 28831) was found active against representative zygomycete fungi and consequently subjected to thorough identification and chemical analyses of secondary metabolites. Confirmation of the initially identified Bacillus spp. was done using 16S rDNA gene sequence analysis which indicated a novel species (accession MF099872) that is closely related to Bacillus siamensis, Bacillus amyloliquefaciens, and Bacillus nakamurai. The crude culture-free filtrate and both chloroform and ethyl acetate extracts authenticated the initial antifungal activity of this strain, which exceeded that of amphotericin B, a standard antifungal agent. GC-MS results of the extracts revealed 32 compounds which included long-chain fatty acids, fatty acid methyl esters, alkaloids, and alcoholic compounds. Seven biologically active compounds were identified from Bacillus spp. strain JS6 and are equally found in the literature originating from plant or microbial sources. In the literature, these compounds show various activities such as antifungal, antioxidant, hypocholesterolemic, nematicide, pesticide, antiandrogenic, flavour, haemolytic, alpha reductase inhibitor, and other antimicrobial activities. The analysis identified a major unique antifungal peak (rt, 23.142; area, 25.36%) as 5,10-Diethoxy-2,3,7,8-tetrahydro-1H,6Hdipyrrolo[1,2-a:1',2'-d]pyrazine, a heterocyclic aromatic organic compound, that has been previously detected in Lactobacillus casei.