Dehalococcoides mccartyi
strains are corrinoid-auxotrophic Bacteria and axenic cultures that require vitamin B
12
(CN-Cbl) to conserve energy via organohalide respiration. Cultures of
D. mccartyi
strains BAV1, GT and FL2 grown with limiting amounts of 1 µg l
−1
CN-Cbl quickly depleted CN-Cbl, and reductive dechlorination of polychlorinated ethenes was incomplete leading to vinyl chloride (VC) accumulation. In contrast, the same cultures amended with 25 µg l
−1
CN-Cbl exhibited up to 2.3-fold higher dechlorination rates, 2.8–9.1-fold increased growth yields, and completely consumed growth-supporting chlorinated ethenes. To explore whether known cobamide-producing microbes supply
Dehalococcoides
with the required corrinoid cofactor, co-culture experiments were performed with the methanogen
Methanosarcina barkeri
strain Fusaro and two acetogens,
Sporomusa ovata
and
Sporomusa
sp. strain KB-1, as
Dehalococcoides
partner populations. During growth with H
2
/CO
2
,
M. barkeri
axenic cultures produced 4.2 ± 0.1 µg l
−1
extracellular cobamide (factor III), whereas the
Sporomusa
cultures produced phenolyl- and
p
-cresolyl-cobamides. Neither factor III nor the phenolic cobamides supported
Dehalococcoides
reductive dechlorination activity suggesting that
M. barkeri
and the
Sporomusa
sp. cannot fulfil
Dehalococcoides
' nutritional requirements.
Dehalococcoides
dechlorination activity and growth occurred in
M. barkeri
and
Sporomusa
sp. co-cultures amended with 10 µM 5′,6′-dimethylbenzimidazole (DMB), indicating that a cobalamin is a preferred corrinoid cofactor of strains BAV1, GT and FL2 when grown with chlorinated ethenes as electron acceptors. Even though the methanogen and acetogen populations tested did not produce cobalamin, the addition of DMB enabled guided biosynthesis and generated a cobalamin that supported
Dehalococcoides
' activity and growth. Guided cobalamin biosynthesis may offer opportunities to sustain and enhance
Dehalococcoides
activity in contaminated subsurface environments.