School of Civil and Environmental Engineering, Georgia Institute of Technology, 311 Ferst Dr., Atlanta, GA 30332-0512, USA.
Appl Environ Microbiol. 2010 Mar;76(5):1417-22. doi: 10.1128/AEM.02816-09. Epub 2010 Jan 15.
Biodegradation of synthetic compounds has been studied extensively, but the metabolic diversity required for catabolism of many natural compounds has not been addressed. 5-Nitroanthranilic acid (5NAA), produced in soil by Streptomyces scabies, is also the starting material for synthetic dyes and other nitroaromatic compounds. Bradyrhizobium JS329 was isolated from soil by selective enrichment with 5NAA. When grown on 5NAA, the isolate released stoichiometric amounts of nitrite and half of the stoichiometric amounts of ammonia. Enzyme assays indicate that the initial step in 5NAA degradation is an unusual hydrolytic deamination for formation of 5-nitrosalicylic acid (5NSA). Cloning and heterologous expression revealed the genes that encode 5NAA deaminase (naaA) and the 5NSA dioxygenase (naaB) that cleaves the aromatic ring of 5NSA without prior removal of the nitro group. The results provide the first clear evidence for the initial steps in biodegradation of amino-nitroaromatic compounds and reveal a novel deamination reaction for aromatic amines.
人们对合成化合物的生物降解进行了广泛的研究，但许多天然化合物的分解代谢所需的代谢多样性尚未得到解决。5-硝基邻氨基苯甲酸（5NAA）是由疮痂链霉菌在土壤中产生的，也是合成染料和其他硝基芳烃化合物的起始原料。通过用 5NAA 进行选择性富集，从土壤中分离出 Bradyrhizobium JS329。当在 5NAA 上生长时，该分离物释放出化学计量的亚硝酸盐和一半化学计量的氨。酶分析表明，5NAA 降解的第一步是一个不寻常的水解脱氨反应，生成 5-硝基水杨酸（5NSA）。克隆和异源表达揭示了编码 5NAA 脱氨酶（naaA）和 5NSA 双加氧酶（naaB）的基因，该酶在不先去除硝基的情况下切割 5NSA 的芳环。这些结果为氨基-硝基芳烃化合物生物降解的初始步骤提供了第一个明确的证据，并揭示了一种新型的芳香胺脱氨反应。
