The present research aimed to evaluate the antibacterial activity of volatile organic compounds (VOCs) produced by octocoral-associated bacteria Bacillus sp. BO53 and Pseudoalteromonas sp. GA327. The volatilome bioactivity of both bacteria species was evaluated against human pathogenic antibiotic-resistant bacteria, methicillin-resistant Staphylococcus aureus, Acinetobacter baumanni, and Pseudomonas aeruginosa. In this regard, the in vitro tests showed that Bacillus sp. BO53 VOCs inhibited the growth of P. aeruginosa and reduced the growth of S. aureus and A. baumanni. Furthermore, Pseudoalteromonas sp. GA327 strongly inhibited the growth of A. baumanni, and P. aeruginosa. VOCs were analyzed by headspace solid-phase microextraction (HS-SPME) joined to gas chromatography-mass spectrometry (GC-MS) methodology. Nineteen VOCs were identified, where 5-acetyl-2-methylpyridine, 2-butanone, and 2-nonanone were the major compounds identified on Bacillus sp. BO53 VOCs; while 1-pentanol, 2-butanone, and butyl formate were the primary volatile compounds detected in Pseudoalteromonas sp. GA327. We proposed that the observed bioactivity is mainly due to the efficient inhibitory biochemical mechanisms of alcohols and ketones upon antibiotic-resistant bacteria. This is the first report which describes the antibacterial activity of VOCs emitted by octocoral-associated bacteria.
Fungi that are known foliar endophytes have often been isolated from leaf-cutting ant fungal gardens. Recent in vitro growth trials showed that endophytic fungal growth was suppressed by the Lepiotaceous fungi cultivated by leaf-cutting ants. Here we conducted experiments with laboratory ant colonies to assess how long one strain of a common endophytic fungus persisted in the ants' fungal garden after incorporation by worker ants. We observed that after 72 hours our focal strain could no longer be cultured from the incorporated leaf material or surrounding garden tissues. Moreover, we were unable to culture our focal strain from the ants' garbage dumps. The limited persistence of an endophyte in ant fungal gardens may be due to ant hygiene behaviors and/or antagonism from the ants' fungal cultivar.
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