Genetics & Developmental Biology Program, Division of Plant & Soil Sciences, West Virginia University, Morgantown, WV, 26506-6108, USA.
Curr Microbiol. 2014 Jan;68(1):1-5. doi: 10.1007/s00284-013-0434-2. Epub 2013 Aug 8.
Production of ergot alkaloids in the opportunistic fungal pathogen Aspergillus fumigatus is restricted to conidiating cultures. These cultures typically accumulate several pathway intermediates at concentrations comparable to that of the pathway end product. We investigated the contribution of different cell types that constitute the multicellular conidiophore of A. fumigatus to the production of ergot alkaloid pathway intermediates versus the pathway end product, fumigaclavine C. A relatively minor share (11 %) of the ergot alkaloid yield on a molar basis was secreted into the medium, whereas the remainder was associated with the conidiating colonies. Entire conidiating cultures (containing hyphae, vesicle of conidiophore, phialides of conidiophore, and conidia) accumulated higher levels of the pathway intermediate festuclavine and lower levels of the pathway end product fumigaclavine C than did isolated, abscised conidia, indicating that conidiophores and/or hyphae have a quantitatively different ergot alkaloid profile compared to that of conidia. Differences in alkaloid accumulation among cell types also were indicated by studies with conidiophore development mutants. A ∆medA mutant, in which conidiophores are numerous but develop poorly, accumulated higher levels of pathway intermediates than did the wildtype or a complemented ∆medA mutant. A ∆stuA mutant, which grows mainly as hyphae and produces very few, abnormal conidiophores, produced no detectable ergot alkaloids. The data indicated heterogeneous spatial distribution of ergot alkaloid pathway intermediates versus pathway end product in conidiating cultures of A. fumigatus. This skewed distribution may reflect differences in abundance or activity of pathway enzymes among cell types of those conidiating cultures.
在机会致病真菌烟曲霉中，麦角生物碱的产生仅限于产分生孢子的培养物。这些培养物通常在几种途径中间体的浓度与途径终产物相当。我们研究了构成烟曲霉多细胞分生孢子的不同细胞类型对麦角生物碱途径中间体与途径终产物，即 fumigaclavine C 的产生的贡献。基于摩尔基础，相对较小的份额（11%）的麦角生物碱产量分泌到培养基中，而其余的则与产分生孢子的菌落相关。整个产分生孢子的培养物（包含菌丝、分生孢子梗的泡囊、分生孢子梗的产孢小梗和分生孢子）积累了更高水平的途径中间体 festuclavine 和更低水平的途径终产物 fumigaclavine C，而不是分离的、脱落的分生孢子，这表明分生孢子梗和/或菌丝与分生孢子相比具有不同的麦角生物碱特征。分生孢子梗发育突变体的研究表明，细胞类型之间在生物碱积累方面存在差异。一个 ∆medA 突变体，其中分生孢子梗数量众多但发育不良，积累了更高水平的途径中间体，而野生型或互补的 ∆medA 突变体则没有。一个 ∆stuA 突变体，主要生长为菌丝，产生很少的异常分生孢子梗，没有检测到麦角生物碱。这些数据表明，在烟曲霉的产分生孢子培养物中，麦角生物碱途径中间体与途径终产物的空间分布不均匀。这种偏斜分布可能反映了不同细胞类型之间途径酶的丰度或活性的差异。
