ABSTRACT
Strain DCL14, which is able to grow on limonene as a sole source of carbon and energy, was isolated from a freshwater sediment sample. This organism was identified as a strain of
Rhodococcus erythropolis
by chemotaxonomic and genetic studies.
R. erythropolis
DCL14 also assimilated the terpenes limonene-1,2-epoxide, limonene-1,2-diol, carveol, carvone, and (−)-menthol, while perillyl alcohol was not utilized as a carbon and energy source. Induction tests with cells grown on limonene revealed that the oxygen consumption rates with limonene-1,2-epoxide, limonene-1,2-diol, 1-hydroxy-2-oxolimonene, and carveol were high. Limonene-induced cells of
R. erythropolis
DCL14 contained the following four novel enzymatic activities involved in the limonene degradation pathway of this microorganism: a flavin adenine dinucleotide- and NADH-dependent limonene 1,2-monooxygenase activity, a cofactor-independent limonene-1,2-epoxide hydrolase activity, a dichlorophenolindophenol-dependent limonene-1,2-diol dehydrogenase activity, and an NADPH-dependent 1-hydroxy-2-oxolimonene 1,2-monooxygenase activity. Product accumulation studies showed that (1
S
,2
S
,4
R
)-limonene-1,2-diol, (1
S
,4
R
)-1-hydroxy-2-oxolimonene, and (3
R
)-3-isopropenyl-6-oxoheptanoate were intermediates in the (4
R
)-limonene degradation pathway. The opposite enantiomers [(1
R
,2
R
,4
S
)-limonene-1,2-diol, (1
R
,4
S
)-1-hydroxy-2-oxolimonene, and (3
S
)-3-isopropenyl-6-oxoheptanoate] were found in the (4
S
)-limonene degradation pathway, while accumulation of (1
R
,2
S
,4
S
)-limonene-1,2-diol from (4
S
)-limonene was also observed. These results show that
R. erythropolis
DCL14 metabolizes both enantiomers of limonene via a novel degradation pathway that starts with epoxidation at the 1,2 double bond forming limonene-1,2-epoxide. This epoxide is subsequently converted to limonene-1,2-diol, 1-hydroxy-2-oxolimonene, and 7-hydroxy-4-isopropenyl-7-methyl-2-oxo-oxepanone. This lactone spontaneously rearranges to form 3-isopropenyl-6-oxoheptanoate. In the presence of coenzyme A and ATP this acid is converted further, and this finding, together with the high levels of isocitrate lyase activity in extracts of limonene-grown cells, suggests that further degradation takes place via the β-oxidation pathway.
摘要
从淡水沉积物样本中分离出了 DCL14 菌株,该菌株能够以柠檬烯作为唯一的碳和能量来源进行生长。经鉴定,该生物属于
Rhodococcus erythropolis
的菌株。
红球菌
DCL14 还吸收萜烯类化合物柠檬烯-1,2-环氧乙烷、柠檬烯-1,2-二醇、香芹酚、香芹酮和 (-)- 薄荷醇,而未将 perillyl 醇用作碳和能量来源。用柠檬烯诱导细胞的试验表明,柠檬烯-1,2-环氧化物、柠檬烯-1,2-二醇、1-羟基-2-氧代柠檬烯和香芹酮的耗氧率很高。柠檬烯诱导的
R. erythropolis
DCL14 细胞含有以下四种参与该微生物柠檬烯降解途径的新型酶活性:依赖于黄素腺嘌呤二核苷酸和 NADH 的柠檬烯-1,2-单加氧酶活性、不依赖于辅助因子的柠檬烯-1,2-环氧化物水解酶活性、依赖于二氯苯酚靛酚的柠檬烯-1,2-二醇脱氢酶活性和依赖于 NADPH 的 1- 羟基-2-氧代柠檬烯-1,2-单加氧酶活性。产物积累研究表明,(1
S
,2
S
,4
R
)-1,2-亚甲基二醇,(1
S
,4
R
)-1-羟基-2-氧代柠檬烯和(3
R
)-3-异丙烯基-6-氧代庚酸酯的中间体。
R
)-柠檬烯降解途径的中间产物。相反的对映体[(1
R
,2
R
,4
S
)-1,2-亚甲基二醇,(1
R
,4
S
)-1-羟基-2-氧代柠檬烯和(3
S
)-3-异丙烯基-6-氧代庚酸酯]中发现了(4S)
S
)-柠檬烯降解途径中,而(1-R)
R
,2
S
,4
S
)-1,2-亚甲基丙烯二醇从(4
S
)-亚甲烯醇中提取的。这些结果表明
R. erythropolis
DCL14 通过一种新的降解途径代谢柠檬烯的两种对映体,该途径首先在 1,2 双键处发生环氧化反应,形成柠檬烯-1,2-环氧化物。这种环氧化物随后会转化为柠檬烯-1,2-二醇、1-羟基-2-氧代柠檬烯和 7-羟基-4-异丙烯基-7-甲基-2-氧代氧杂环庚酮。这种内酯会自发地重新排列形成 3-异丙烯基-6-氧代庚酸酯。在辅酶 A 和 ATP 的存在下,这种酸会进一步转化,这一发现以及柠檬烯生长细胞提取物中高水平的异柠檬酸裂解酶活性表明,进一步降解是通过 β 氧化途径进行的。