Fusaricidin B

A bacterial strain showing strong antifungal activity was isolated from yellow loess and was identified as Paenibacillus kribbensis CU01. Insoluble mucoidal polymers were separated from M9 culture medium via low-speed centrifugation. Most antifungal activity was associated with substances in the insoluble precipitate, which was purified by reverse phase high performance liquid chromatography. Purified fractions were analyzed using matrix-assisted laser desorption/ionization time-of-flight/time-of-flight mass spectrometry. Two major ion peaks with mass-to-charge ratio values (m/z) at 883.6 and 897.6 were revealed. After alkaline hydrolysis and sequence analysis, two cyclic depsipeptides were identified as, fusaricidin A and fusaricidin B. Their production was significantly increased by the addition of glucose, Fe2+ , and Mn2+ to M9 medium. Maximum concentrations of produced fusaricidin A and fusaricidin B at flask-scale comprised 460 mg L-1 and 118 mg L-1 , respectively: the highest production concentrations yet reported in the literature. This demonstrates that P. kribbensis CU01 has enormous commercial potential for the mass production of fusaricidin.

Fusaricidins B, C and D, new depsipeptide antibiotics, have been isolated as minor components from the culture broth of Bacillus polymyxa KT-8 which was obtained from the rhizosphere of garlic suffering from the basal rot caused by Fusarium oxysporum. The structure of fusaricidin B has been elucidated mainly by various NMR experiments coupled with amino acid analysis in relation to fusaricidin A, the main component of the complex, whose structure was reported previously. The fraction consisting of fusaricidins C and D was unsuccessfully separated, giving roughly a 4:1 mixture of the two, respectively. The structures of fusaricidins C and D have been determined within the mixture by detailed analyses of the 2D NMR spectra. Fusaricidins B, C and D are active against fungi and Gram-positive bacteria almost as well as fusaricidin A.

The discovery of antibiotics heralded an era of improved health care. However, the over-prescription and misuse of antibiotics resulted in the development of resistant strains of various pathogens. Since then, there has been an incessant search for discovering novel compounds from bacteria at various locations with extreme conditions. The soil is one of the most explored locations for bioprospecting. In recent times, hypersaline environments and symbiotic associations have been investigated for novel antimicrobial compounds. Among the extreme environments, hot springs are comparatively less explored. Many researchers have reported the presence of microbial life and secretion of antimicrobial compounds by microorganisms in hot springs. A pioneering research in the corresponding author's laboratory resulted in the identification of the antibiotic Fusaricidin B isolated from a hot spring derived eubacteria, Paenibacillus polymyxa, which has been assigned a new application for its anti-tubercular properties. The corresponding author has also reported anti-MRSA and anti-VRE activity of 73 bacterial isolates from hot springs in India.