National Agriculturally Important Microbial Culture Collection (NAIMCC), ICAR-National Bureau of Agriculturally Important Microorganisms, Kushmaur, Maunath Bhanjan, 275 103, Uttar Pradesh, India.
FEMS Microbiol Lett. 2020 Jan 15;367(24). doi: 10.1093/femsle/fnaa190.
Genus Micrococcus is considered a high IAA producer. However, interestingly, there is no report on the tryptophan- independent pathway operation in this genus. Consequently, the present study was undertaken to evaluate high IAA production by Micrococcus aloeverae DCB-20 and generate reasonable evidence for the occurrence of the tryptophan-independent pathway. Strain DCB-20 produced a high quantity of 880.51 µM or 154.3 µg/mL IAA in LB broth supplemented with L-tryptophan. The tryptophan-independent pathway operation was supported by IAA production in Tris-minimal broth (TM broth) medium supplemented with acid hydrolyzed casein hydrolysate (casein acid hydolysate), which lacks tryptophan. The HPLC analysis showed the absence of tryptophan either from exogenous or endogenous sources in TM broth in the presence of casein acid hydrolysate inoculated with M. aloeverae DCB-20. The absence of tryptophan was further confirmed by the appearance of non-pigmented colonies of Chromobacterium violaceum strain TRFM-24 on Tris-minimal agar (TM agar) containing acid-hydrolyzed casein. This is probably the first report on IAA biosynthesis by M. aloeverae DCB-20 employing tryptophan-independent pathway. This simple technique can also be adapted to detect operation of the tryptophan-independent pathway in other bacteria.
微球菌属被认为是高 IAA 产生菌。然而，有趣的是，在该属中没有关于色氨酸非依赖途径操作的报道。因此，本研究旨在评估 DCB-20 对耐辐射球菌产生高 IAA 的能力，并为色氨酸非依赖途径的发生提供合理的证据。菌株 DCB-20 在补充 L-色氨酸的 LB 肉汤中产生了大量的 880.51 µM 或 154.3 µg/mL IAA。色氨酸非依赖途径的操作得到了补充有酸水解酪蛋白水解物（酪蛋白酸水解物）的 Tris 最小肉汤（TM 肉汤）培养基中 IAA 产生的支持，该培养基缺乏色氨酸。HPLC 分析表明，在添加了酪蛋白酸水解物的 TM 肉汤中，无论是外源性还是内源性来源，都不存在色氨酸，耐辐射球菌 DCB-20 的接种也不存在色氨酸。在含有酸水解酪蛋白的 Tris 最小琼脂（TM 琼脂）上，出现了非色素化的 Chromobacterium violaceum 菌株 TRFM-24 的菌落，进一步证实了色氨酸的缺失。这可能是首次报道耐辐射球菌 DCB-20 采用色氨酸非依赖途径合成 IAA。该简单技术也可以适应于检测其他细菌中色氨酸非依赖途径的操作。
