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Antimicrobial Agents and Chemotherapy, October 2007, p. 3537-3545, Vol. 51, No. 10
0066-4804/07/$08.00+0     doi:10.1128/AAC.00442-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Fatty Acid Synthesis Is Essential for Survival of Cryptococcus neoformans and a Potential Fungicidal Target

Department of Medicine,¹ Molecular Genetics and Microbiology, Duke University Medical Center, Durham, North Carolina, 27710,² Department of Medicine, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok 10700, Thailand³

Received 30 March 2007/ Returned for modification 1 June 2007/ Accepted 1 August 2007

Fatty acid synthase in the yeast Cryptococcus neoformans is composed of two subunits encoded by FAS1 and FAS2 genes. We inserted a copper-regulated promoter (P_CTR4-2) to regulate FAS1 and FAS2 expression in Cryptococcus neoformans (strains P_CTR4-2/FAS1 and P_CTR4-2/FAS2, respectively). Both mutants showed growth rates similar to those of the wild type in a low-copper medium in which FAS1 and FAS2 were expressed, but even in the presence of exogenous fatty acids, strains were suppressed in growth under high-copper conditions. The treatment of C. neoformans with fluconazole was shown to have an increased inhibitory activity and even became fungicidal when either FAS1 or FAS2 expression was suppressed. Furthermore, a subinhibitory dose of fluconazole showed anticryptococcal activity in vitro in the presence of cerulenin, a fatty acid synthase inhibitor. In a murine model of pulmonary cryptococcosis, a tissue census of yeast cells in P_CTR4-2/FAS2 strain at day 7 of infection was significantly lower than that in mice treated with tetrathiomolybdate, a copper chelator (P < 0.05), and a yeast census of P_CTR4-2/FAS1 strain at day 14 of infection in the brain was lower in the presence of more copper. In fact, no positive cultures from the brain were detected in mice (with or without tetrathiomolybdate treatment) infected with the P_CTR4-2/FAS2 strain, which implies that this mutant did not reach the brain in mice. We conclude that both FAS1 and FAS2 in C. neoformans are essential for in vitro and in vivo growth in conditions with and without exogenous fatty acids and that FAS1 and FAS2 can potentially be fungicidal targets for C. neoformans with a potential for synergistic behavior with azoles.

Published ahead of print on 13 August 2007.

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• Kingsbury, J. M., McCusker, J. H. (2008). Threonine biosynthetic genes are essential in Cryptococcus neoformans. Microbiology 154: 2767-2775 [Abstract] [Full Text]