Abstract
Despite the threat of Fusarium dieback posed due to ambrosia fungi cultured by ambrosia beetles such as Euwallacea spp., the wood-degradation mechanisms utilized by ambrosia fungi are not fully understood. In this study, we analyzed the 16S rRNA and 18S rRNA genes of the microbial community from the Ficus tree tunnel excavated by Euwallacea interjectus and isolated the cellulose-degrading fungus, Fusarium spp. strain EI, by enrichment culture with carboxymethyl cellulose as the sole carbon source. The cellulolytic enzyme secreted by the fungus was identified and expressed in Pichia pastoris, and its enzymatic properties were characterized. The cellulolytic enzyme, termed FsXEG12A, could hydrolyze carboxymethyl cellulose, microcrystalline cellulose, xyloglucan, lichenan, and glucomannan, indicating that the broad substrate specificity of FsXEG12A could be beneficial for degrading complex wood components such as cellulose, xyloglucan, and galactoglucomannan in angiosperms. Inhibition of FsXEG12A function is, thus, an effective target for Fusarium dieback caused by Euwallacea spp.
Highlights
Euwallacea spp. is a genus of ambrosia beetles distributed over Asia into Israel, Central America, and in at least five different locations within the United States
Isolation of fungi from E. interjectus (Fig. 1a) was performed, and only Fusarium spp. strain EI was isolated using MM liquid medium containing carboxymethyl cellulose (CMC). These results suggested that Fusarium spp. strain EI was a cellulose-degrading symbiotic fungus found in E. interjectus
A protein band of approximately 25-kDa with cellulolytic activity was identified as EMT67806.1 by peptide mass fingerprinting and MS/MS spectrum analysis using MALDI-TOF/TOF–MS (Fig. 3b and Additional file 1: Table S1). These results indicate that Fusarium spp. strain EI predominantly secretes a cellulolytic enzyme with high similarity to EMT67806.1 in liquid MM medium containing 1.0% CMC
Summary
Euwallacea spp. is a genus of ambrosia beetles distributed over Asia into Israel, Central America, and in at least five different locations within the United States. These beetles penetrate wood packaging and plant material (Haack 2006; Kirkendall and Ødegaard 2007; O’Donnell et al 2015; Ploetz et al 2016; Wingfield et al 2010). Ambrosia beetles including Euwallacea spp. carry fungi in specialized structures on their integument called mycangia. Symbiotic fungi (consistent associates) often include only two to three partners per ambrosia beetle species. Fusarium spp., termed AF 1–12, were identified, and the dominant fungal symbiont of Euwallacea interjectus was a specialized ambrosia fungus, Fusarium sp. Fusarium spp., termed AF 1–12, were identified, and the dominant fungal symbiont of Euwallacea interjectus was a specialized ambrosia fungus, Fusarium sp. strain AF-3 (O’Donnell et al 2015)
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