K. Kusel et al., Physiological ecology of Clostridium glycolicum RD-1, an aerotolerant acetogen isolated from sea grass roots, APPL ENVIR, 67(10), 2001, pp. 4734-4741
An anaerobic, H-2-utilizing bacterium, strain RD-1, was isolated from the h
ighest growth-positive dilution series of a root homogenate prepared from t
he sea grass Halodule wrightii. Cells of RD-1 were gram-positive, spore-for
ming, motile rods that were linked by connecting filaments. Acetate was pro
duced in stoichiometries indicative of an acetyl coenzyme A (acetyl-CoA) pa
thway-dependent metabolism when RD-1 utilized H-2-CO2, formate, lactate, or
pyruvate. Growth on sugars or ethylene glycol yielded acetate and ethanol
as end products. RD-1 grew at the expense of glucose in the presence of low
initial concentrations (up to 6% [vol/vol]) of O-2 in the headspace of sta
tic, horizontally incubated culture tubes; the concentration of O-2 decreas
ed during growth in such cultures. Peroxidase, NADH oxidase, and superoxide
dismutase activities were detected in the cytoplasmic fraction of cells gr
own in the presence of O-2. In comparison to cultures incubated under stric
tly anoxic conditions, acetate production decreased, higher amounts of etha
nol were produced, and lactate and H-2 became significant end products when
RD-1 was grown on glucose in the presence of O-2. Similarly, when RD-1 was
grown on fructose in the presence of elevated salt concentrations, lower a
mounts of acetate and higher amounts of ethanol and HZ were produced. When
the concentration of O-2 in the headspace exceeded 1% (vol/vol), supplement
al H-2 was not utilized. The 16S rRNA gene of RD-1 had a 99.7% sequence sim
ilarity to that of Clostridium glycolicum DSM 1288(T), an organism characte
rized as a fermentative anaerobe. Comparative experiments with C. glycolicu
m DSM 1288(T) demonstrated that it had negligible H-2- and formate-utilizin
g capacities. However, carbon monoxide dehydrogenase was detected in both R
D-I and C. glycolicum DSM 1288(T). A 91.4% DNA-DNA hybridization between th
e genomic DNA of RD-1 and that of C. glycolicum DSM 1288(T) confirmed that
RD-I was a strain of C. glycolicum. These results indicate that (i) RD-I me
tabolizes certain substrates via the acetyl-CoA pathway, (ii) RD-1 can tole
rate and consume limited amounts of O-2, (iii) oxic conditions favor the pr
oduction of ethanol, lactate, and H-2 by RD-1, and (iv) the ability of RD-1
to cope with limited amounts of O-2 might contribute to its survival in a
habitat subject to daily gradients of photosynthesis-derived O-2.