The recently identified causative agent of white-nose syndrome (WNS), Pseudogymnoascus destructans, has been implicated in the mortality of an estimated 5.5 million North American bats since its initial documentation in 2006 (Frick et al. in Science 329:679-682, 2010). In an effort to identify potential biological and chemical control options for WNS, 6 previously described bacterially produced volatile organic compounds (VOCs) were screened for anti-P. destructans activity. The compounds include decanal; 2-ethyl-1-hexanol; nonanal; benzothiazole; benzaldehyde; andN,N-dimethyloctylamine. P. destructans conidia and mycelial plugs were exposed to the VOCs in a closed air space at 15 and 4 °C and then evaluated for growth inhibition. All VOCs inhibited growth from conidia as well as inhibiting radial mycelial extension, with the greatest effect at 4 °C. Studies of the ecology of fungistatic soils and the natural abundance of the fungistatic VOCs present in these environments suggest a synergistic activity of select VOCs may occur. The evaluation of formulations of two or three VOCs at equivalent concentrations was supportive of synergistic activity in several cases. The identification of bacterially produced VOCs with anti-P. destructans activity indicates disease-suppressive and fungistatic soils as a potentially significant reservoir of biological and chemical control options for WNS and provides wildlife management personnel with tools to combat this devastating disease.
BackgroundThe recently-identified causative agent of White-Nose Syndrome (WNS), Pseudogymnoascus destructans, has been responsible for the mortality of an estimated 5.5 million North American bats since its emergence in 2006. A primary focus of the National Response Plan, established by multiple state, federal and tribal agencies in 2011, was the identification of biological control options for WNS. In an effort to identify potential biological control options for WNS, multiply induced cells of Rhodococcus rhodochrous strain DAP96253 was screened for anti-P. destructans activity.ResultsConidia and mycelial plugs of P. destructans were exposed to induced R. rhodochrous in a closed air-space at 15°C, 7°C and 4°C and were evaluated for contact-independent inhibition of conidia germination and mycelial extension with positive results. Additionally, in situ application methods for induced R. rhodochrous, such as fixed-cell catalyst and fermentation cell-paste in non-growth conditions, were screened with positive results. R. rhodochrous was assayed for ex vivo activity via exposure to bat tissue explants inoculated with P. destructans conidia. Induced R. rhodochrous completely inhibited growth from conidia at 15°C and had a strong fungistatic effect at 4°C. Induced R. rhodochrous inhibited P. destructans growth from conidia when cultured in a shared air-space with bat tissue explants inoculated with P. destructans conidia.ConclusionThe identification of inducible biological agents with contact-independent anti- P. destructans activity is a major milestone in the development of viable biological control options for in situ application and provides the first example of contact-independent antagonism of this devastating wildlife pathogen.
Snake fungal disease (SFD), caused by the ascomycete Ophidiomyces ophiodiicola, has been associated with severe morbidity and mortality of numerous species of wild snakes in 15 US states. Accordingly, SFD was added to the horizon scan of global conservation issues in 2014. Due to the itinerant and secluded nature of many snake species, as well as the diversity of species impacted by SFD, estimating SFD-associated mortalities has been challenging. Regardless, the impacts have been shown to be significant in local and regional instances. Currently there is no known therapeutic or prophylactic for SFD. This study evaluated a potential biological treatment option for SFD that has shown promise in managing white-nose syndrome in bats, the bacterium Rhodococcus rhodochrous DAP 96253. R. rhodochrous was evaluated for in vitro contact-independent antagonism of O. ophiodiicola, with positive results. Additionally, synthetic volatile organic compounds (VOCs) associated with fungistatic soils were evaluated individually and in combinations to determine their potential for use as chemical control agents of SFD. In all cases an inhibitory effect was observed and statistically significant (p<0.05) radial growth inhibition was observed in several cases. The results presented in this study provide initial evidence for the in vivo evaluation of the potential of these agents to prevent or reduce the morbidity and mortality associated with SFD.
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