title: Regulatory cascade and biological activity ofBeauveria bassianaoosporein that limits bacterial growth after host death.
abstract: The regulatory network and biological functions of the fungal secondary metabolite oosporein have remained obscure.Beauveria bassianahas evolved the ability to parasitize insects and outcompete microbial challengers for assimilation of host nutrients. A novel zinc finger transcription factor, BbSmr1 (B. bassianasecondary metabolite regulator 1), was identified in a screen for oosporein overproduction. Deletion ofBbsmr1resulted in up-regulation of the oosporein biosynthetic gene cluster (OpSgenes) and constitutive oosporein production. Oosporein production was abolished in double mutants ofBbsmr1and a second transcription factor,OpS3, within the oosporein gene cluster (ΔBbsmr1ΔOpS3), indicating that BbSmr1 acts as a negative regulator ofOpS3expression. Real-time quantitative PCR and a GFP promoter fusion construct ofOpS1, the oosporein polyketide synthase, indicated thatOpS1is expressed mainly in insect cadavers at 24-48 h after death. Bacterial colony analysis inB. bassiana-infected insect hosts revealed increasing counts until host death, with a dramatic decrease (∼90%) after death that correlated with oosporein production. In vitro studies verified the inhibitory activity of oosporein against bacteria derived from insect cadavers. These results suggest that oosporein acts as an antimicrobial compound to limit microbial competition onB. bassiana-killed hosts, allowing the fungus to maximally use host nutrients to grow and sporulate on infected cadavers.
authors.affiliation: Biotechnology Research Center, Southwest University, Chongqing 400715, China; fyh@swu.edu.cn.
authors.forename: Yanhua
authors.initials: Y
authors.lastname: Fan
authors.affiliation: Biotechnology Research Center, Southwest University, Chongqing 400715, China.
authors.forename: Xi
authors.initials: X
authors.lastname: Liu
authors.affiliation: Department of Microbiology and Cell Science, University of Florida, Gainesville, FL 32611.
authors.forename: Nemat O
authors.initials: NO
authors.lastname: Keyhani
authors.affiliation: Biotechnology Research Center, Southwest University, Chongqing 400715, China.
authors.forename: Guirong
authors.initials: G
authors.lastname: Tang
authors.affiliation: Biotechnology Research Center, Southwest University, Chongqing 400715, China.
authors.forename: Yan
authors.initials: Y
authors.lastname: Pei
authors.affiliation: Biotechnology Research Center, Southwest University, Chongqing 400715, China.
authors.forename: Wenwen
authors.initials: W
authors.lastname: Zhang
authors.affiliation: Biotechnology Research Center, Southwest University, Chongqing 400715, China.
authors.forename: Sheng
authors.initials: S
authors.lastname: Tong
mesh_terms: D000818:Animals; D052982:Beauveria / Q000235:genetics / Q000378:metabolism*; D016227:Benzoquinones / Q000378:metabolism*; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D015966:Gene Expression Regulation, Fungal / Q000235:genetics; D053263:Gene Regulatory Networks / Q000235:genetics; D007313:Insecta / Q000382:microbiology; D005810:Multigene Family / Q000235:genetics; D048630:Polyketide Synthases / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D015854:Up-Regulation / Q000235:genetics; D014774:Virulence / Q000235:genetics
chemical_list: D016227:Benzoquinones; D005656:Fungal Proteins; D014157:Transcription Factors; C008706:oosporein; D048630:Polyketide Synthases
keywords: Beauveria bassiana; biological role; fungal–bacterial competition; oosporein; transcription factor