Dataset Information

Regulatory cascade and biological activity of Beauveria bassiana oosporein that limits bacterial growth after host death.

ABSTRACT: The regulatory network and biological functions of the fungal secondary metabolite oosporein have remained obscure. Beauveria bassiana has evolved the ability to parasitize insects and outcompete microbial challengers for assimilation of host nutrients. A novel zinc finger transcription factor, BbSmr1 (B. bassiana secondary metabolite regulator 1), was identified in a screen for oosporein overproduction. Deletion of Bbsmr1 resulted in up-regulation of the oosporein biosynthetic gene cluster (OpS genes) and constitutive oosporein production. Oosporein production was abolished in double mutants of Bbsmr1 and a second transcription factor, OpS3, within the oosporein gene cluster (?Bbsmr1?OpS3), indicating that BbSmr1 acts as a negative regulator of OpS3 expression. Real-time quantitative PCR and a GFP promoter fusion construct of OpS1, the oosporein polyketide synthase, indicated that OpS1 is expressed mainly in insect cadavers at 24-48 h after death. Bacterial colony analysis in B. 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 on B. bassiana-killed hosts, allowing the fungus to maximally use host nutrients to grow and sporulate on infected cadavers.

SUBMITTER: Fan Y

PROVIDER: S-EPMC5338512 | biostudies-literature | 2017 Feb

REPOSITORIES: biostudies-literature

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Regulatory cascade and biological activity of Beauveria bassiana oosporein that limits bacterial growth after host death.

Fan Yanhua Y Liu Xi X Keyhani Nemat O NO Tang Guirong G Pei Yan Y Zhang Wenwen W Tong Sheng S

Proceedings of the National Academy of Sciences of the United States of America 20170213 9

The regulatory network and biological functions of the fungal secondary metabolite oosporein have remained obscure. Beauveria bassiana has evolved the ability to parasitize insects and outcompete microbial challengers for assimilation of host nutrients. A novel zinc finger transcription factor, BbSmr1 (B. bassiana secondary metabolite regulator 1), was identified in a screen for oosporein overproduction. Deletion of Bbsmr1 resulted in up-regulation of the oosporein biosynthe ...[more]

PMID: 28193896

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Project description:The entomopathogenic fungus Beauveria bassiana can produce the secondary metabolite oosporein under alkaline conditions or in fungus-killed cadavers. However, the regulatory mechanism of oosporein synthesis is not fully understood. In thisstudy, we found that the pH signaling transcription factor BbPacC is involved in the regulation of oosporein production. Overexpression of BbPacC promotes oosporein production in B. bassiana at pH 6.0 or under alkaline conditions (pH 8.0), but deletion of this gene abolished oosporein production. Under acidic conditions (pH 4.0), no oosporein production was observed in the wild-type and BbPacC overexpression strains. Yeast one-hybrid assays and electrophoretic mobility shift assay (EMSA) confirmed the binding ability of BbPacC with 4 putative PacC-binding sites in the promoter region of BbOpS3, a transcription factor located in the oosporein synthetic gene cluster regulating the expression of oosporein synthetic genes. Overexpression of Bbmsn2, a previously reported negative regulator of oosporein synthesis, in OEPacC or wild-type strains abolished oosporein production in all tested conditions. However, deletion of Bbmsn2 in the BbPacC overexpression strain significantly improved oosporein production even at pH 4.0. These results indicated that BbPacC is a positive regulator of oosporein production and functions jointly with Bbmsn2 to regulate oosporein production in different environments and particularly under alkaline conditions. IMPORTANCE B. bassiana produces the red dibenzoquinone pigment oosporein under certain specific conditions, such as alkaline conditions and fungus-killed cadavers. Ooporein possesses antibiotic and insect immune inhibition activities and plays multiple roles during the infection process of B. bassiana against insect hosts. Several negative regulators involved in oosporein synthesis have been reported; however, we know little about the positive regulators outside the biosynthetic gene cluster. Here, we found that the pH signaling transcription factor BbPacC positively regulates oosporein production by binding to several PacC-binding sites. In addition, our results also indicate that BbPacC jointly acts with the negative regulator Bbmsn2 to regulate oosporein synthesis. Our results provide insight into understanding the regulatory mechanism of oosporein production as well as targets to engineer B. bassiana strains producing high levels of oosporein.

Dataset Information

Regulatory cascade and biological activity of Beauveria bassiana oosporein that limits bacterial growth after host death.

Publications

Regulatory cascade and biological activity of <i>Beauveria bassiana</i> oosporein that limits bacterial growth after host death.

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