Department of Microbiology, University of Tennessee, Knoxville, Tennessee, USA.
Appl Environ Microbiol. 2012 Sep;78(18):6630-6. doi: 10.1128/AEM.01535-12. Epub 2012 Jul 6.
Dehalococcoides mccartyi strains conserve energy from reductive dechlorination reactions catalyzed by corrinoid-dependent reductive dehalogenase enzyme systems. Dehalococcoides lacks the ability for de novo corrinoid synthesis, and pure cultures require the addition of cyanocobalamin (vitamin B(12)) for growth. In contrast, Geobacter lovleyi, which dechlorinates tetrachloroethene to cis-1,2-dichloroethene (cis-DCE), and the nondechlorinating species Geobacter sulfurreducens have complete sets of cobamide biosynthesis genes and produced 12.9 ± 2.4 and 24.2 ± 5.8 ng of extracellular cobamide per liter of culture suspension, respectively, during growth with acetate and fumarate in a completely synthetic medium. G. lovleyi-D. mccartyi strain BAV1 or strain FL2 cocultures provided evidence for interspecies corrinoid transfer, and cis-DCE was dechlorinated to vinyl chloride and ethene concomitant with Dehalococcoides growth. In contrast, negligible increase in Dehalococcoides 16S rRNA gene copies and insignificant dechlorination occurred in G. sulfurreducens-D. mccartyi strain BAV1 or strain FL2 cocultures. Apparently, G. lovleyi produces a cobamide that complements Dehalococcoides' nutritional requirements, whereas G. sulfurreducens does not. Interestingly, Dehalococcoides dechlorination activity and growth could be restored in G. sulfurreducens-Dehalococcoides cocultures by adding 10 μM 5',6'-dimethylbenzimidazole. Observations made with the G. sulfurreducens-Dehalococcoides cocultures suggest that the exchange of the lower ligand generated a cobalamin, which supported Dehalococcoides activity. These findings have implications for in situ bioremediation and suggest that the corrinoid metabolism of Dehalococcoides must be understood to faithfully predict, and possibly enhance, reductive dechlorination activities.
地杆菌属能够从钴胺素依赖型还原脱卤酶酶系统催化的还原脱卤反应中保存能量。地杆菌属缺乏从头合成钴胺素的能力，纯培养需要添加氰钴胺素（维生素 B12）才能生长。相比之下，能够将四氯乙烯还原为顺式-1,2-二氯乙烯（顺式-DCE）的脱硫地杆菌以及非脱卤物种脱硫地杆菌具有完整的 cobamide 生物合成基因，并且在完全合成培养基中使用乙酸盐和延胡索酸盐生长时，分别产生了 12.9 ± 2.4 和 24.2 ± 5.8 ng/L 细胞外 cobamide。G. lovleyi-D. mccartyi 菌株 BAV1 或菌株 FL2 共培养提供了种间钴胺素转移的证据，同时伴随着地杆菌属的生长，顺式-DCE 被还原为氯乙烯和乙烯。相比之下，在 G. sulfurreducens-D. mccartyi 菌株 BAV1 或菌株 FL2 共培养中，地杆菌属 16S rRNA 基因拷贝数几乎没有增加，脱卤作用也微不足道。显然，G. lovleyi 产生了一种 cobamide，可以补充地杆菌属的营养需求，而 G. sulfurreducens 则不能。有趣的是，通过添加 10 μM 5',6'-二甲基苯并咪唑，可以在 G. sulfurreducens-地杆菌属共培养中恢复地杆菌属的脱氯活性和生长。在 G. sulfurreducens-地杆菌属共培养中观察到的现象表明，配体的交换产生了一种 cobamide，它支持了地杆菌属的活性。这些发现对原位生物修复具有重要意义，并表明必须了解地杆菌属的钴胺素代谢，以准确预测并可能增强还原脱卤活性。
