Syntrophomonas wolfei Gottingen

Classification

Higher order taxa

Domain: Bacteria Phylum: Firmicutes Class: Clostridia Order: Clostridiales Family: Syntrophomonadceae Genus: Syntrophomonas Species: Syntrophomas wolfei

Species

Syntrophomonas wolfei

Description and Significance

S. wolfei is a gram-negative, slightly helical rod with round ends that possesses between two to eight flagella laterally inserted along the concave side of the cell (McInerney, et, al., 1981). A Gram stain of this species showed the multilayered cell wall to have a gram-negative composition. S. wolfei is an anaerobic bacterium that β-oxidizes short-chain saturated fatty acids, four to eight carbons in length, to acetate and propionate (from odd-numbered fatty acids) only when grown in coculture with H2-using bacteria such as methanogens (Beaty and McInerney, 1990). The species was isolated in coculture with either a non-fatty acid-degrading, H2-utilizing Desulfovibrio sp. or methanogens (McInerney, et, al., 1981). It has been determined that growth and degradation of fatty acids, by S. wolfei, occur only in syntrophic association with H2-using bacteria. S. wolfei uses fatty acids between 4 and 8 carbons in length for it carbon source, as a result of fatty acid degradation methane gas is produced. S. wolfei does not require oxygen because of its anaerobic metabolism and thus is found in aquatic sediments or digester sludge. This organism is particularly important to the environment, because of its capability to β-oxidizes saturated fatty acids; it is often used in bioremediation.

Genome Structure

Like most bacteria, S. wolfei contains one circular chromosome, with 2,936,195 base pairs, coding for 2,504 proteins, although 2642 genes are coded for. The GC content of the genome is 44.9% and 82% of the genome is code region. The genome also codes of 68 structural RNAs and 70 psuedogenes. It has been shown that genes DVU2103, DVU2104 and DVU2108 code for syntrophic activity in S. wolfei (Scholten, et. al., 2007).

Cell Structure and Metabolism

The cell wall of S. wolfei is about 50 nm wide and is a complex example of the gram-negative cell-wall type. It has a resolvable outer membrane with an irregular contour and a well-defined double-tracked cytoplasmic membrane. The periplasmic space contains a double-tracked layer and a homogeneous electron-dense layer adjacent to the cytoplasmic membrane (McInerney, et, al., 1981). S. wolfei cells are slightly helical rod shape with round ends that possesses two to eight flagella laterally inserted along the concave side of the cell (McInerney, et, al., 1981). Pure culture of S. wolfei provide the best analysis of the membrane phospholipid fatty acids (PLFAs), which show monounsaturated 16:1w7c and 16:1w9c and the saturated 16:0 and 14:0 are the major membrane PLFAs (Henson, et. al., 1988). S. wolfei cell wall’s also contain poly-β-hydroxybutyrate (PHB), which is resistant to digestion in alcohol, ether and sodium hypochlorite (McInerney, et, al., 1981).

S. wolfei was the first bacterium known to obtain energy for growth from the anaerobic degradation of the normal monocarboxylic, saturated, 4-8 carbon fatty acids with dihydrogen and acetate as the products (McInerney, et, al., 1981). Methanogen microbes such as Methanospirillum hungatei are able to keep the presence of hydrogen gas low, which is essential for the degradation of fatty acids by S. wolfei (Beaty and McInerney, 1990). This is the principle behind the syntrophic relationship between S. wolfei and methanogen microbes. On its own S. wolfei is typically difficult to culture. S. wolfei grows well in medium that is anaerobically prepared by boiling under an 80% N2-20% CO2 gas phase. Solid sodium bicarbonate is added, the medium must then be dispensed into serum tubes sealed and autoclaved. The cysteine-sulfide reducing solution and the vitamin solutions are then added to each tube several hours before inoculation. All vitamin solutions must be filtered sterilized and made anoxic by aseptically evacuating and repressurizing the tube with O2-free nitrogen (Beaty and McInerney, 1990). High concentrations of acetate and lactate altered the electron flow in cocultures, resulting in the formation of less methane and more butyrate and caproate, this shows that the metabolism of S. wolfei was inhibited by high levels of organic acid anions. The activity of acetate-using methanogens is important for the syntrophic degradation of fatty acids when high levels of acetate are present (Beaty and McInerney, 1989).

Ecology

S. wolfei can typically be found in aquatic sediments, such as the anoxic zone of a Winogradsky column, or digester sludge. S. wolfei can also be cultured in labs with a syntrophic relationship with H2 using microorganisms, such as methanogens. S. wolfei is part of an important symbiotic relationship where methanogen microbes such as Methanospirillum hungatei are able to keep the presence of hydrogen gas low, which is essential for the degradation of fatty acids by S. wolfei. S. wolfei has also been contemplated for use in bioremediation because it can be used to manage ecosystems to reduce greenhouse gas emissions and to enhance biological methane production from industrial and municipal wastes.

Current Research

S. wolfei has been used as a model for syntrophic behavior for the study of the mechanism by which this syntrophic association occurs. As a result a better understanding of the syntrophic relationship has been reached in the scientific community. S. wolfei has also played a prominent role in the development of bioremediation, which is the use of microbes to clean-up the environment. Also S. wolfei has been used as an example of horizontal gene flow. It has recently been shown that the syntrophic activity may be a result of ancient horizontal gene transfer (Scholten, et. al., 2007). Recent research with Syntrophomas wolfei has included the discovery of new subspecies. One study isolated a spore forming species of bacteria from rice field mud and demonstrated through phylogenetic analysis that based on 16S rRNA gene similarity showed that new strain 4J5T was most closely related to Syntrophomonas wolfei (Wu, et. al., 2007). Other recent studies have also isolated new species closely related to the Syntrophomonas genus; almost all of these newly isolated bacteria are also capable of fatty acid degradation 4-8 carbons in length, when cultured with H2 using microbes. More recent research in bioremediation has shown fermentation of propionate and butyrate cannot be catabolized by dehalogenating bacteria or methanogenic consortia and, thus, the existence of fatty acid-oxidizing bacteria in the mixed culture is crucial for dechlorination. Butyrate can be catabolized by Syntrophomonas wolfei through -oxidation to acetate and hydrogen or formate (Chen, 2003). This shows one of the many practical uses for the ability of Syntrophomas wolfei to oxidize fatty acids.

References

Amos, D.A., and McInerney, M.J. 2004. Poly-β-hydroxyalkanoate in Syntrophomonas wolfei. Archives of Microbiology, v. 152, p. 172-177.

Beaty, P.S., and McInerney, M.J. 1989. Effects of organic acid anions on the growth and metabolism of Syntrophomonas wolfei in pure culture and in defined consortia. Applied and Environmental microbiology, v. 55, p. 977-983.

Beaty, P.S., and McInerney, M.J. 1990. Nutritional features of Syntrophomonas wolfei. Applied and Environmental microbiology, v. 56, p. 3223-3224.

Beaty, P.S., Wofford, N.Q., McInerney, M.J. 1987. Separation of Syntrophomonas wolfei from Methanospirillum hungatii in syntrophic cocultures by using percoll gradients. Applied and Environmental Microbiology, v. 53, p. 1183-1185.

Chen, G. 2003. Reductive dehalogenation of tetrachloroethylene by microorganisms: current knowledge and application strategies. Applied Microbiology and Biotechnology, v. 63, p. 373-377.

Henson, J.M., McInerney, M.J., Beaty, P.S., Nickels, J., White, D.C. 1988. Phospholipid fatty acid composition of the syntrophic anaerobic bacterium Syntrophomonas wolfei. Applied and Environmental Microbiology, v. 54, p. 1570-1574.

McInerney, M.J., Bryant, M.P., Hespell, R.B., Costerton, J.W. 1981. Syntrophomonas wolfei gen. nov. sp. nov., an anaerobic, syntrophic, fatty acid-oxidizing bacterium. Applied and Environmental Microbiology, v. 41, p. 1029-1039.

Scholten, J.C., Culley, D.E., Brockman, F.J., Wu, G., Zhang, W. 2007. Evolution of the syntrophic interaction between Desulfovibrio vulgaris and Methanosarcina barkeri: involvement of an ancient horizontal gene transfer. Journal: Biochemical and Biophysical Research Communications, v. 352, p. 48-54.

Wofford, N.Q., Beaty, P.S., McInerney, M.J. 1986. Preparation of cell-free extracts and the enzymes involved in fatty acid metabolism in Syntrophomonas wolfei. Journal of Bacteriology, v. 167, p. 179-185.

Wu, C., Dong, X., Liu, X. 2007. Syntrophomonas wolfei subsp. methylbutyratica subsp. nov., and assignment of Syntrophomonas wolfei subsp. saponavida to Syntrophomonas saponavida sp. nov. comb. nov. Systematic and Applied Microbiology, v. 30, p. 376-380.