Borgia P T, Dodge C L
Department of Medical Microbiology and Immunology, School of Medicine, Southern Illinois University, Springfield 62794-9230.
J Bacteriol. 1992 Jan;174(2):377-83. doi: 10.1128/jb.174.2.377-383.1992.
By screening for the osmotically remediable phenotype, mutations in two genes (orlA and orlB) affecting the cell wall chitin content of Aspergillus nidulans were identified. Strains carrying temperature-sensitive alleles of these genes produce conidia which swell excessively and lyse when germinated at restrictive temperatures. Growth under these conditions is remedied by osmotic stabilizers and by N-acetylglucosamine (GlcNAc). Remediation by GlcNAc suggests that the mutations affect early steps in the synthesis of chitin. Temperature and medium shift experiments indicate that the phenotype is the result of decreased synthesis rather than increased chitin degradation and that osmotic stabilizers act to stabilize a defective wall rather than to stabilize the gene product. Two genes, orlC and orlD, which affect cell wall beta-1,3-glucan content were also identified. Walls from strains carrying mutations in these genes exhibit normal amounts of alpha-1,3-glucan and chitin but reduced amounts of beta-1,3-glucan. As for the chitin-deficient mutants, orlC and orlD mutants spontaneously lyse on conventional media but are remedied by osmotic stabilizers. These results indicate that both chitin and beta-1,3-glucan are likely to contribute to the structural rigidity of the cell wall.
通过筛选可经渗透压补救的表型，鉴定出了影响构巢曲霉细胞壁几丁质含量的两个基因（orlA和orlB）中的突变。携带这些基因温度敏感等位基因的菌株产生的分生孢子在限制温度下发芽时会过度膨胀并裂解。在这些条件下的生长可通过渗透压稳定剂和N-乙酰葡糖胺（GlcNAc）得到补救。GlcNAc的补救作用表明这些突变影响几丁质合成的早期步骤。温度和培养基转换实验表明，该表型是合成减少的结果，而非几丁质降解增加的结果，并且渗透压稳定剂的作用是稳定有缺陷的细胞壁，而非稳定基因产物。还鉴定出了影响细胞壁β-1,3-葡聚糖含量的两个基因orlC和orlD。携带这些基因中突变的菌株的细胞壁显示出正常量的α-1,3-葡聚糖和几丁质，但β-1,3-葡聚糖的量减少。与几丁质缺陷型突变体一样，orlC和orlD突变体在常规培养基上会自发裂解，但可通过渗透压稳定剂得到补救。这些结果表明，几丁质和β-1,3-葡聚糖都可能有助于细胞壁的结构刚性。
