Living on Acetylene. A Primordial Energy Source - The Metal-Driven Biogeochemistry of Gaseous Compounds in the Environment - page 19

extracts. As for P. acetylenicus , it required a strong reductant and the presence of
molybdate or tungstate in the growth media. However, a cross reaction with
antibodies against the acetylene hydratase from P. acetylenicus was not found [ 18 ].
Recently, a more systematic study was conducted on the presence of acetylene
hydratase activity in anoxic sediments and waters from all over the United States of
America and several deep sea sites [ 19 ]. Acetylene consumption was found in only
21 % of the samples investigated, usually after an incubation time of several days
to months. The lag phase was explained by selecting for and thereby enriching
bacteria that thrive on acetylene. This would mean that acetylene-fermenting
bacteria were rather scarce in the original samples. In a second part of the study,
the authors tried to amplify genes coding for an acetylene hydratase from DNA
extracted from the sediment and water samples. The use of primers synthesized
from the acetylene hydratase gene of P. acetylenicus resulted in 63 PCR products
out of 645 environmental samples (9.8 %) [ 19 ]. Since AH-like genes could not be
amplified in all samples in which acetylene hydratase activity was found, it was
argued that the primer may have been overly specific for the acetylene hydratase
gene of P. acetylenicus , hence, that Miller et al. could amplify the genes from
Pelobacter -like organisms but not from other, less closely related bacteria [ 19 ].

3.1 Pelobacter acetylenicus

Pelobacter acetylenicus was isolated 1985 by enrichment on acetylene, which can
be used as sole source of carbon and energy by this bacterium [ 17 ]. Two strains
are deposited at the DSMZ culture collection in Braunschweig (Germany). The type
strain WoAcy1 (DSMZ 3246) was isolated from a freshwater creek sediment
and strain GhAcy1 (DSMZ 3247) from a marine sediment. Pelobacter are Gram-
negative, strictly anaerobic deltaproteobacteria that ferment low-molecular-weight
organic compounds, but no sugars. Characteristic substrates are gallic acid, acetoin,
polyethylene glycol, and acetylene [ 20 ]. Pelobacter acetylenicus is mesophilic and
grows between pH 6.0 and pH 8.0. From over 40 different substrates tested, only
acetylene, acetoin, ethanolamine, and choline supported growth directly, while
1,2-propanediol and glycerol could be used in the presence of acetate [ 17 ].
No growth was found on the acetylene derivatives acetylene carboxylate or acety-
lene dicarboxylate or the structurally related compounds ethylene and cyanide.
During growth of P. acetylenicus , acetylene is fermented to nearly equal
amounts of ethanol and acetate and small amounts of acetaldehyde [ 17 ]. According
to the metabolic scheme proposed by Schink in 1985, the energetics of the initial
hydration of acetylene can be derived (equations 1 and 2 )[ 17 ]:

G ' 0 ¼

9 kJ mol 1 C 2 H 2 þ

! ʔ ð Þ

H 2 O CH 3 CHO 119 : 1