- This study evaluated the potential of the aerobic Mycobacterium strain JS6O to
grow on a variety of organic acid substrates, and the possible effects an organic acid
would have on the degradation rate of vinyl chloride (VC). A series of batch growth
tests were designed to determine the time it took to consume the substrate and the overall
increase in biomass. Strain JS6O was found capable of growth on acetate, propionate,
and butyrate, but could not grow on formate or lactate. Acetate was chosen for further
study because strain JS6O consumed acetate the most rapidly of all the organic acids
tested, and acetate is a common product of fermentation reactions in the subsurface.
Strain JS6O was confirmed to grow on both ethylene and vinyl chloride as the sole
carbon and energy source. Comparatively, strain JS6O's rate of growth on VC is much
slower than that of ethylene. With acetate as an augmenting growth substrate, ethylene
and VC utilization rates increased by 30% and 48%, respectively. Since acetate and VC
are often found together in contaminated chlorinated ethene plumes, this makes a strong
case for natural attenuation of VC by strain JS6O.
A series of kinetic tests were implemented to determine the K[subscript s] and k[subscript max] of strain
JS6O for ethylene, VC, and c-DCE. The K[subscript s] and k[subscript max] for ethylene determined through
NLSR methods was similar to the values published in Coleman et al. (2002), supporting
the maintenance of a pure culture throughout the experimental work.
When strain JS6O was exposed to the isomers of DCE (trans-1,2-dichloroethylene
(t-DCE), cis-1,2-dichloroethylene (c-DCE), and 1,1-dichloroethylene (1,1-DCE)) the
cells were unable to grow on these compounds. However, when growing on acetate,
strain JS6O cometabolized c-DCE and t-DCE, but not 1,1-DCE, with c-DCE transformed
more rapidly than t-DCE. Transformation of c-DCE was also observed with growth on
VC and ethylene. The presence of c-DCE was shown to partially inhibit VC degradation,
but had no effect on ethylene degradation. The cometabolism results with acetate further
indicate that strain JS6O is a good candidate for natural attenuation of multiple
chlorinated ethenes in the subsurface.