Two strains of airborne Nocardiopsis alba producing different volatile organic compounds (VOCs) as biofungicide for Ganoderma boninense.

Nocardiopsis are actinobacteria which produce active compounds, such as antifungals and volatile compounds. Ganoderma boninense is a pathogenic and aggressive fungus that decreases palm oil yield during production. In this study, we isolated two strains of Nocardia (GME01 and GME22) from airborne contaminants on the actinobacteria culture collection in the laboratory. The aim of this study is to identify two strains of Nocardiopsis and to obtain the antifungal potency of volatile organic compounds (VOCs) against G. boninese. We characterized the morphology using Scanning Electrone Microscope (SEM), molecular properties and whole-cell protein spectra using Matrix Assisted Laser Desorption Ionization Time of Flight Mass Spectrometry (MALDI-TOF MS), antifungal assay on G. boninense and VOCs analysis of Nocardia using solid phase micro extraction/gas chromatography (SPME/GC). The two Nocardiopsis strains had the similar characteristic such as white aerial mycelium and spores, aerobic, grow well on ISP-2, TSA and NA medium without diffusible pigment and had the highest similarity with Nocardiopsis alba DSM 43377 (99.63% and 99.55% similarity for GME01 and GME22, respectively), Different morphological feature was found in aerial mycelium and spores. GME22 has a clearly fragmented mycelium whereas GME01 has none. Other features also showed different on the whole-cell protein spectra, antifungal activity and VOCs profiles. Antifungal activity assay on G. boninense showed that N. alba GME22 has higher antifungal activity than GME01 related with the VOCs abundance in two strains. Almost 38.3% (18 VOCs) of N. alba GME22 and 25.5% (12 VOCs) of N. alba GME01 were found specifically in each strain, and 36.2% (the 17 same VOCs) produced by both. The known volatile antifungal compounds S-methyl ethanethioate, 1,2-dimethyldisulfane, acetic acid, 2-methyl propanoic acid, 3-methyl-butanoic acid, nonan-2-one, undecan-2-one and 2-isopropyl-5-methylcyclohexan-1-ol only produced by N. alba GME22 and 1,3-dimethyltrisulfane only produced by N. alba GME01. A total of two known antifungal compounds 1,2-dimethyldisulfane and 6-methylheptan-2-one were produced by both N. alba. The abundance of antifungal VOCs produced by these bacteria is potentially to be used as biocontrol agent for pathogenic fungi in plants.