Selection of KYC 3270, a Cellulolytic Myxobacteria of Sorangium cellulosum, against Several Phytopathogens and a Potential Biocontrol Agent against Gray Mold in Stored Fruit

Department of Biomedical Sciences, Sun Moon University, Asan 330-744, Korea (Received on July 18, 2011; Revised on August 19, 2011; Accepted on August 20, 2011)During 2002−2008 in Korea, 455 extracts from myxo-bacteria consisting of 318 cellulolytic and 137 bacterio-lytic myxobacteria were isolated, which were then screen-ed for antifungal activity against the phytopathogensBotrytis cinerea, Colletotrichum acutatum, Penicilliumsp. , Pyricularia grisea, and Phytophthora capsici. 204isolates had antifungal activity, causing both a clearzone due to blocked spore germination and inhibitionof mycelial growth; most (199) were from cellulolytic(Sorangium cellulosum) and only five were from bac-teriolytic myxobacteria. B. cinerea, the best controlledamong the five tested pathogens, had a unique group ofantifungal isolates of myxobacterial extracts comparedto the other pathogens’ groups. Among seventy-ninebioactive myxobacteria, four isolates, KYC 3130, KYC3247, KYC 3248 and KYC 3270, were selected and allwere cellulolytic. Liquid culture filtrates of these fourmyxobacteria were applied to tomato, cherry tomato,strawberry, and kiwi fruits 5 h before inoculation withgray mold conidia; then the treated fruits were placedin an airtight container and the experiment was repeat-ed six to eight times. Incidence (%) of gray mold onfruit of the infected control treatment was 84−98%,whereas it was only 5−21% after the KYC 3270 treat-ment. After KYC 3270 treatment of the four fruits,mold control was 79−95%, which was highest amongthe filtrates and statistically the same as treatment withfludioxonil, a registered chemical against gray mold ofstored fruits. Keywords :antifungal activity, Botrytis cinerea, cellulolyticmyxobacteria, strawberryMyxobacteria have a fruiting body with bacteriolytic orcellulolytic characteristics (Cho, 2001; Dawid, 2000; Kimand Son, 2001; Kim et al., 2003a). The cellulolytic myxo-bacteria are able to degrade cellulose, grow well, and can beisolated in culture medium containing cellulose. So far, twospecies of cellulolytic myxobacteria are known, Sorangiumcellulosum and Byssovorax cruenta (Reichenbach, 2001). S. cellulosum produces more than 30 different bioactivemetabolites, including ambruticin, chivosalzole, disorazole,eliamid, epothilone, etnangien, jerangolid, ratjadon, socein,sorangicin, soraphen, spirodienal, spirangien, and tartrolon,which comprise 48% of the bioactive metabolites of myxo-bacteria (Dawid, 2000; Gerth et al., 2003; Niggemann et al.,2002). Most bioassays for biological activity of myxobacteriahave been with bacteriolytic myxobacteria such as Myxo-coccus spp. (Ahn and Kim, 2002; Bull et al., 2002; Chunget al., 2008; Kim and Yun, 2011; Kim et al., 1998; Kim etal., 2003b; Krug et al., 2008), although the antifungalactivity of S. cellulosum, a cellulolytic myxobacterium,against several phytopathogenic fungi has been examinedin Germany (Reichenbach and Hofle, 1994). Soraphen andepothilone are two natural products of S. cellulosum, andsoraphen in particular is an antifungal compound. In fieldtrials, this compound completely inhibited apple scab fungi(Venturia inaequalis) and also prevented grape gray mold(Botrytis cinerea) (Reichenbach and Hofle, 1994). Accord-ing to the paper disk method for dual culture, Spirodienal C,new metabolites from S. cellulosum, have antifungal activityagainst B. cinerea , Botryosphaeria dothideaand Sclerotiniasclerotiorum (Ahn, 2009). Hence, such a cellulolytic myxo-bacterium has extraordinary ability to produce secondarymetabolites with biological activity (Gerth, 2003); however,more cellulolytic myxobacteria containing similar naturalproducts have yet to be studied. B. cinerea is a phytopathogen on more than 200 speciesunder humid and low temperature conditions during storage(Hang et al., 2005; Kulakiotu et al., 2004; Tian et al., 2002;Williamson et al., 2007). To control B. cinerea in Koreanfields, many fungicides having different modes of actionwere developed, e.g., benzimidazole, dicarboximide, sulf-amide, N-phenylcarbamate, phenylpyrrol, and anilinopyri-midine (Choi et al., 1999, 2009a). However, A B. cinerearesistance to benzimidazole through a change of amino acidresidue in β-tubulin was discovered (Soung and Sung,