The Relevance of a Study of a Temperature-sensitive Ballooning Mutant of Aspergillus nidulans Defective in Mannose Metabolism to our Understanding of Mannose as a Wall Component and Carbon/Energy Source

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Abstract
An isolated, temperature-sensitive mutant strain of A. nidulans failed to grow normally on minimal agar medium at 43.degree. C unless mannose was supplied as a sole C source. The mutant was given the symbol MNRA455 for mannose relief. Under restrictive conditions (43.degree. C) the mutant produced extensive areas of swollen hyphae, called balloons. Wall preparations from cultures grown at 40.degree. C had approximately 1/3 of the mannose found in walls of control cultures. The MNRA455 strain produced a more thermolabile phosphomannose mutase than the wild-type strain, so the mutation may be in the structural gene coding for this enzyme. The MNRA455 strain failed to grow on minimal agar medium containing 0.1% (wt/vol) mannose and 0.9% (wt/vol) glucose at 43.degree. C. This property obtained revertants, one of which was a double mutant MNRA1. MNRA455 MANA1. Growth of the double mutant in media containg [14C]mannose at 43.degree. C showed that 84% of the label found in the wall occurred in mannose in comparison with 33% in the wild-type control. Autoradiography of cultures of the double mutant using [3H]mannose showed predominant incorporation of label into the tip region of growing hyphae. A MANA1 strain, isolated following haploidization of diploid, was unable to grow on media containing glucose or mannose alone. The MANA1 strain had reduced phosphomannose isomerase (EC 5.3.1.8) activity. The MANA1 mutation, which is epistatic to MNRA455, was located to linkage group VIII and the MNRA455 mutation to linkage group V. A pathway is presented for the utilization of mannose in A. nidulans.