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Eukaryotic Cell, November 2009, p. 1692-1705, Vol. 8, No. 11
1535-9778/09/$08.00+0     doi:10.1128/EC.00227-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Chitinases Are Essential for Sexual Development but Not Vegetative Growth in Cryptococcus neoformans{triangledown} ,{dagger}

Lorina G. Baker,1 Charles A. Specht,2 and Jennifer K. Lodge1*

Department of Molecular Microbiology, Washington University School of Medicine, 660 S. Euclid Avenue, St. Louis, Missouri 63110,1 Department of Medicine, University of Massachusetts, 364 Plantation Street, Worcester, Massachusetts 016052

Received 6 August 2009/ Accepted 27 August 2009

Cryptococcus neoformans is an opportunistic pathogen that mainly infects immunocompromised individuals. The fungal cell wall of C. neoformans is an excellent target for antifungal therapies since it is an essential organelle that provides cell structure and integrity. Importantly, it is needed for localization or attachment of known virulence factors, including melanin, phospholipase, and the polysaccharide capsule. The polysaccharide fraction of the cryptococcal cell wall is a complex structure composed of chitin, chitosan, and glucans. Chitin is an indispensable component of many fungal cell walls that contributes significantly to cell wall strength and integrity. Fungal cell walls are very dynamic, constantly changing during cell division and morphogenesis. Hydrolytic enzymes, such as chitinases, have been implicated in the maintenance of cell wall plasticity and separation of the mother and daughter cells at the bud neck during vegetative growth in yeast. In C. neoformans we identified four predicted endochitinases, CHI2, CHI21, CHI22, and CHI4, and a predicted exochitinase, hexosaminidase, HEX1. Enzymatic analysis indicated that Chi2, Chi22, and Hex1 actively degraded chitinoligomeric substrates. Chi2 and Hex1 activity was associated mostly with the cellular fraction, and Chi22 activity was more prominent in the supernatant. The enzymatic activity of Hex1 increased when grown in media containing only N-acetylglucosamine as a carbon source, suggesting that its activity may be inducible by chitin degradation products. Using a quadruple endochitinase deletion strain, we determined that the endochitinases do not affect the growth or morphology of C. neoformans during asexual reproduction. However, mating assays indicated that Chi2, Chi21, and Chi4 are each involved in sexual reproduction. In summary, the endochitinases were found to be dispensable for routine vegetative growth but not sexual reproduction.

* Corresponding author. Mailing address: Department of Molecular Microbiology, Washington University School of Medicine, 660 S. Euclid Avenue, Campus Box 8230, St. Louis, MO 63104. Phone: (314) 286-2125. Fax: (314) 362-7325. E-mail: lodgejk{at}wustl.edu

{triangledown} Published ahead of print on 4 September 2009.

{dagger} Supplemental material for this article may be found at http://ec.asm.org/.

Eukaryotic Cell, November 2009, p. 1692-1705, Vol. 8, No. 11
1535-9778/09/$08.00+0     doi:10.1128/EC.00227-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

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