Antifungal activity of bacteria isolated from Japanese frog skin against plant pathogenic fungi

Abstract

Frogs carry bacterial communities on their skin (Harris et al., 2009) that benefit the host frogs by preventing harmful pathogen infections. Our study aimed to collect culturable bacteria from the skin of wild frogs sampled in Japan and evaluate the antagonistic activity of the bacteria toward plant pathogenic fungi. A collection of 106 bacterial isolates was obtained from three species of frogs, namely Hyla japonica, Pelophylax porosus porosus and Buergeria burgeri. Using a dual-culture method, three isolates, HjD52, HjD92 and B341, were selected based on their ability to significantly inhibit the growth of Colletotrichum orbiculare, the causal fungus of cucumber anthracnose disease. These three bacterial isolates also showed a broad-spectrum of antagonistic activity against plant pathogenic fungi. Furthermore, spray treatment with the bacterial suspensions (109 cfu/ml) effectively reduced the number of anthracnose lesions in greenhouse-grown, potted cucumber plants. Based on the 16S rDNA sequence analysis and similarity search, isolates HjD57, HjD92 and B341 were identified as Paenibacillus sp., Raoultella sp. and Citrobacter sp., respectively. This is the first report showing the potential of Paenibacillus sp., Raoultella sp. and Citrobacter sp. from frog skin to serve as potent biocontrol agents against plant diseases.