Sa. Brausstromeyer et al., DICHLOROMETHANE AS THE SOLE CARBON SOURCE FOR AN ACETOGENIC MIXED CULTURE AND ISOLATION OF A FERMENTATIVE, DICHLOROMETHANE-DEGRADING BACTERIUM, Applied and environmental microbiology, 59(11), 1993, pp. 3790-3797
Dichloromethane (DCM) is utilized by the strictly anaerobic, acetogeni
c mixed culture DM as a sole source of carbon and energy for growth. G
rowth with DCM was linear, and cell suspensions of the culture degrade
d DCM with a specific activity of 0.47 mkat/kg of protein. A mass bala
nce of 2 mol of chloride and 0.42 mol of acetate per mol of DCM was ob
served. The dehalogenation reaction showed similar specific activities
under both anaerobic and aerobic conditions. Radioactivity from [C-14
]DCM in cell suspensions was recovered largely as (CO2)-C-14 (58%), [C
-14]acetate (23%), and [C-14]formate (11%), which subsequently disappe
ared. This suggested that formate is a major intermediate in the pathw
ay from DCM to acetate. Efforts to isolate from culture DM a pure cult
ure capable of anaerobic growth with DCM were unsuccessful, although o
verall acetogenesis and the partial reactions are thermodynamically fa
vorable. We then isolated bacterial strains DMA, a strictly anaerobic,
gram-positive, endospore-forming rod, and DMB, a strictly anaerobic,
gram-negative, endospore-forming homoacetogen, from culture DM. Both s
train DMB and Methanospirillum hungatei utilized formate as a source o
f carbon and energy. Coculture of strain DMA with either M. hungatei o
r strain DMB in solid medium with DCM as the sole added source of carb
on and energy was observed. These data support a tentative scheme for
the acetogenic fermentation of DCM involving interspecies formate tran
sfer from strain DMA to the acetogenic bacterium DMB or to the methano
gen M. hungatei.