粪产碱菌的Tn5转座诱变及吲哚乙酸生物合成特性的研究

粪产碱菌(Alcaligenes faecalis)A1501的吲哚乙酸(IAA)合成需要外源色氨酸参与。在不含色氨酸的限制性培养基中，A1501能良好生长，但不能合成IAA，表明在A1501中存在一条依赖于色氨酸的IAA合成途径。A1501的IAA合成具有菌体密度依赖特性。采用Tn5转座诱变技术构建A1501的突变库，从3500多株Tn5转染子中分离到一株色氨酸营养缺陷型突变株AT63。该Tn5突变株在不含色氨酸的限制性培养基上不能生长，但仍能进行IAA的生物合成，每毫升菌体密度等于10的突变株菌体的IAA合成量为224μg。对突变株AT63的研究表明在A1501中至少存在两条IAA合成途径：一条以色氨酸为合成前体，另一条以吲哚-3-磷酸甘油为前体。Southern杂交结果表明突变株中Tn5插入位点可能位于编码色氨酸合成酶基因上。

TN5 MUTAGENESIS AND THE CHARACTERISTICS OF INDOLE-3-ACETIC ACID BIOSYNTHESIS IN ALCALIGENES FAECALIS A1501

The IAA production of Alcaligenes faecalis wild type strain A1501 depended on addition of L-tryptopham(trp). A1501 could grow well in minimal medium without Trp, but could not produce IAA. The results indicated that there was Trp-dependent IAA biosynthesis pathway in A. faecalis A1501. A1501 shows a characteristic of cell density-dependent IAA biosynthesis. The Tn5-induced mutant bank of A1501 was constructed using Tn5 mutagenesis and one Trp auxotrophic mutant AT63 was selected and identified. The Tn5-induced mutant AT63 could synthesis 2.24 micrograms/mL IAA in minimal medium without L-Trp. It indicated there were at least two IAA biosynthesis pathways in A. faecalis, one needed Trp, the other needed IGP as precursor. The results of southern hybridization also suggested that the Tn5-insertion might locate in gene locus encoded IAA synthetase.