Pichia mexicana, a New Heterothallic Yeast from Cereoid Cacti in the North American Sonoran Desert

Abstract

A description is given of a novel member of the yeast genus Pichia that was recovered 13 times in the Sonoran Desert from necrotic tissue of cereoid cacti. Most of the isolates came from organ-pipe cacti. The new yeast occurs in the cactus “rot pockets“ in the haploid condition and is heterothallic. Upon mixing of appropriate mating types, zygotes developed with hat-shaped ascospores. Physiologically, the haploid strains resemble Candida tenuis, but this species has a different habitat and shares only 9.2% of its nuclear deoxyribonucleic acid base sequences with P. mexicana. The sexual state is physiologically similar to P. stipitis and an as yet undescribed cactus-specific species of the genus Clavispora, but their deoxyribonucleic acid sequence complementarity is less than 1% compared with P. mexicana. The base composition of the nuclear deoxyribonucleic acid of P. mexicana ranged from 42.2 to 43.0 mol% guanine plus cytosine (five strains). The type strain of P. mexicana is UCD-FST 76-308A (= ATCC 42175 = CBS 7066) and the complementary mating type is UCD-FST 76-391B ( = ATCC 42176 = CBS 7067).