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Altering the expression of two chitin synthase genes differentially affects the growth and morphology of Aspergillus oryzae

Center for Process Biotechnology, BioCentrum-DTU building, 223, Søltofts Plads, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark¹
Novozymes A/S, 2880 Bagsværd, Denmark²

Author for correspondence: Jens Nielsen. Tel: +45 4525 2696. Fax: +45 4588 4148. e-mail: jn{at}biocentrum.dtu.dk

In Aspergillus oryzae, one full-length chitin synthase (chsB) and fragments of two other chitin synthases (csmA and chsC) were identified. The deduced amino acid sequence of chsB was similar (87% identity) to chsB from Aspergillus nidulans, which encodes a class III chitin synthase. The sequence obtained for csmA indicated that it had high similarity to class V chitin synthases. chsB and csmA disruption strains and a strain in which chsB transcription was controlled were constructed using the nitrite reductase (niiA) promoter. The strains were examined during hyphal growth by Northern analysis, analysis of the cell-wall composition and growth in the presence of Calcofluor white (CFW). The chsB disrupted strain and the uninduced p_niiA–chsB strain exhibited hyperbranching, they had a lower level of conidiation than the wild-type and were sensitive to CFW at 50 mg l^-1. When chsB transcription was induced in the strain containing the p_niiA–chsB construct, the strain displayed wild-type morphology on solid medium and at sub-maximum growth rates but the wild-type morphology was not fully restored during rapid growth in batch cultivation. The csmA disruption strain displayed morphological abnormalities, such as ballooning cells, intrahyphal hyphae and conidial scars. The growth was severely inhibited in the presence of 10 mg CFW l^-1. In none of the constructed strains did the cell-wall composition differ from the wild-type. Northern analysis indicated no change in the transcription of the chitin synthase genes csmA and chsC when chsB expression was altered, and there was no change in the transcription of chsB and chsC when csmA was disrupted.

Keywords: N-acetylglucosamine, cell wall

Abbreviations: CFW, Calcofluor white

The GenBank accession numbers for the chsB, chsC and chsA gene sequences reported in this paper are AY029261, AF410464 and AF429307, respectively.

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