Morphological transitions governed by density dependence and lipoxygenase activity in Aspergillus flavus
Morphological transitions governed by density dependence and lipoxygenase activity in Aspergillus flavus
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DOI：
10.1128/aem.00565-08
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发表时间：
2008-09-01
影响因子：
4.4
通讯作者：
Keller, N. P.
中科院分区：
文献类型：
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作者：
Brown, S. Horowitz;Zarnowski, R.;Keller, N. P.
黄曲霉分化产生无性分散孢子（分生孢子）或称为菌核的越冬存活结构。此处描述的结果表明，这两个过程受密度依赖机制的反向调控，并且细胞密度增加（从每平板10¹到10⁷个细胞）导致菌核数量最少，分生孢子数量最多。来自低细胞密度培养物的废培养基提取物诱导出高菌核数量表型，而高细胞密度提取物则增加了分生孢子形成。密度依赖的发育也受脂质可利用性变化的影响。外源亚油酸在中等细胞密度（每平板10⁴和10⁵个细胞）下增加了菌核的产生，而油酸和亚麻酸抑制菌核形成。编码脂氧合酶（LOX）的Aflox缺失极大地减少了菌核和分生孢子的密度依赖发育，导致在高细胞密度（>10⁵个细胞/平板）下菌核数量总体增加，分生孢子数量减少。Aflox突变体显示亚油酸LOX活性降低。综上所述，这些结果表明存在一种群体感应机制，其中在密集培养物中产生的一种（或多种）因子，也许是一种LOX衍生的代谢物，激活分生孢子形成，而在低密度培养物中产生的一种（或多种）因子刺激菌核形成。
Aspergillus flavus differentiates to produce asexual dispersing spores (conidia) or overwintering survival structures called sclerotia. Results described here show that these two processes are oppositely regulated by density-dependent mechanisms and that increasing the cell density (from 10(1) to 10(7) cells/plate) results in the lowest numbers of sclerotial and the highest numbers of conidial. Extract from spent medium of low-cell-density cultures induced a high-sclerotium-number phenotype, whereas high-cell-density extract increased conidiation. Density-dependent development is also modified by changes in lipid availability. Exogenous linoleic acid increased sclerotial production at intermediate cell densities (10(4) and 10(5) cells/plate), whereas oleic and linolenic acids inhibited sclerotium formation. Deletion of Aflox encoding a lipoxygenase (LOX) greatly diminished density-dependent development of both sclerotia and conidia, resulting in an overall increase in the number of sclerotia and a decrease in the number of conidia at high cell densities (> 10(5) cells/plate). Aflox mutants showed decreased linoleic acid LOX activity. Taken together, these results suggest that there is a quorum-sensing mechanism in which a factor(s) produced in dense cultures, perhaps a LOX-derived metabolite, activates conidium formation, while a factor(s) produced in low-density cultures stimulates sclerotium formation.