Nd. Gray et al., ECOPHYSIOLOGICAL EVIDENCE THAT ACHROMATIUM-OXALIFERUM IS RESPONSIBLE FOR THE OXIDATION OF REDUCED SULFUR SPECIES TO SULFATE IN A FRESH-WATER SEDIMENT, Applied and environmental microbiology, 63(5), 1997, pp. 1905-1910
Achromatium oxaliferum is a large, morphologically conspicuous, sedime
nt-dwelling bacterium, The organism has yet to be cultured in the labo
ratory, and very little is known about its physiology, The presence of
intracellular inclusions of calcite and sulfur have given rise to spe
culation that the bacterium is involved in the carbon and sulfur cycle
s in the sediments where it is found, Depth profiles of oxygen concent
ration and A, oxaliferum cell numbers in a freshwater sediment reveale
d that the A, oxaliferum population spanned the oxic-anoxic boundary i
n the top 3 to 4 cm of sediments, Some of the A, oxaliferum cells resi
ded at depths where no oxygen was detectable, suggesting that these ce
lls may be capable of anaerobic metabolism, The distributions of solid
-phase and dissolved inorganic sulfur species in the sediment revealed
that A. oxaliferum was most abundant where sulfur cycling was most in
tense, The sediment was characterized by low concentrations of free su
lfide, However, a comparison of sulfate reduction rates in sediment co
res incubated with either oxic or anoxic overlying water indicated tha
t the oxidative and reductive components of the sulfur cycle were tigh
tly coupled in the A, oxaliferum-bearing sediment, A positive correlat
ion between pore mater sulfate concentration and A, oxaliferum numbers
was observed in field data collected over an 18-month period, suggest
ing a possible link between A, oxaliferum numbers and the oxidation of
reduced sulfur species to sulfate, The field data were supported by l
aboratory incubation experiments in which sodium molybdate-treated sed
iment cores were augmented with highly purified suspensions of A, oxal
iferum cells, Under oxic conditions, rates of sulfate production in th
e presence of sodium molybdate were found to correlate strongly,vith t
he number of cells added to sediment cores, providing further evidence
for a role for A, oxaliferum in the oxidation of reduced sulfur.