ABSTRACT
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.
摘要
人们对合成化合物的生物降解进行了广泛的研究,但对许多天然化合物分解代谢所需的代谢多样性还没有涉及。5-Nitroanthranilic acid (5NAA)是由疥癣链霉菌(Streptomyces scabies)在土壤中产生的。
疥疮链霉菌
也是合成染料和其他硝基芳香族化合物的起始原料。
Bradyrhizobium
JS329 是通过选择性富集 5NAA 从土壤中分离出来的。当在 5NAA 上生长时,该分离菌释放出等量的亚硝酸盐和等量氨的一半。酶测定结果表明,5NAA 降解的第一步是形成 5-亚硝基水杨酸(5NSA)的不寻常水解脱氨过程。克隆和异源表达揭示了编码 5NAA 脱氨酶(naaA)的基因。
naaA
)和 5NSA 二氧酶(naaB
naaB
) 的基因,它们能裂解 5NSA 的芳香环而不事先去除硝基。这些结果为氨基硝基芳香族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基反应。