Syntrophic bacteria

Stable metabolic associations generally between pairs of anaerobic bacteria have been termed syntrophs, and these are effective in degrading a number of aliphatic carboxylic acids or benzoate under anaerobic conditions. These reactions have been discussed in reviews (Schink 1991, 1997 Lowe et al. 1993) that provide lucid accounts of the role of syntrophs in the degradation of complex organic matter. Two examples are given here to illustrate the experimental intricacy of the problems besetting the study of syntrophic metabolism under anaerobic conditions ... 

Lidstrom-O Connor ME, GL Fulton, AE Wopat (1983) Methylobacterium ethanolicum a syntrophic association of two methylotrophic bacteria. J Gen Microbiol 129 3139-3148. 

Stams AIM, JB van Dijk, C Dijkema, CM Plugge (1993) Growth of syntrophic propionate-oxidizing bacteria with fumarate in the absence of methanogenic bacteria. Appl Environ Microbiol 59 1114-1119. 

FIGURE i Diagrammatic representation of the structure and function of bacterial biofilms. Dissolved organic matter (DOM) is sorbed onto the biofilm (1), additional DOM is released from algae and organic particles (2). The organic matter is cleaved by extracellular enzymes (3). Interactions can occur between clones of syntrophic or competing bacteria (4). See Section II for details. 

They occur in anaerobic sediments rich in sulfide and elemental sulfur, and live syntrophically with the phototrophic green sulfur bacteria (Chlorobi-aceae) that photooxidize H2S to S and excrete sulfur extracellularly. Desulfuromonas regenerate H2S by sulfur respiration, using, at least in part, organic matter leaked by Chlombium cells. 

Harmsen H. J. M., Kengen H. M. P., Akkermans A. D. L., Stams A. J. M., and De Vos W. M. (1996b) Detection and localization of syntrophic propionate-oxidizing bacteria in granular sludge by in situ hybridization using 16S rRNA-based oligonucleotide probes. Appl. Environ. Microbiol. 62, 1656-1663. 

KnoU G. and Winter J. (1989) Degradation of phenol via carboxylation to benzoate by a defined, obligate syntrophic consortium of anaerobic bacteria. Appl. Microbiol. Biotech. 30, 318-324. 

Davis concluded that shikimic acid was a common precursor of phenylalanine, tyrosine, tryptophan, p-aminobenzoic acid, p-hydroxybenzoic acid, and an unknown sixth factor, and he next set out to determine other substances lying on the biosynthetic pathway. The various mutants were therefore tested for syntrophism, i.e., for the ability of one mutant to produce a substance necessary for the growth of another mutant. There was thus found a thermolabile substance, X, which was a true precursor of shikimic acid (184). X was isolated from culture filtrates and identified as 5-dehydroshikimic acid (744). Similar experiments revealed a substance, W, which was a true precursor of substance X (187, 193). This also was isolated and shown to be 5-dehydroquinic acid (906). The enzyme, named 5-dehydroquinase, converting dehydroquinic acid to dehydroshikimic acid has been partially purified (606). It is fairly stable, has a high specificity, appears to have no cofactors, and is of wide occurrence in bacteria, algae, yeasts, and plants but, as expected, could not be found in mammalian liver. 

In natural ecosystems the sulfur cycle should be in balance, meaning that the amount of sulfide that is oxidized should correspond to the amount of sulfate that is reduced. Such a balance can be found in a sulfuretum . This is a syntrophical community of bacteria in which H2S produced by sulfate reducing bacteria is reoxidized by the sulfur compound oxidizing bacteria. 

Furukawa Y, Inubushi K (2002) Feasible suppression technique of methane emission from paddy soil by iron amendment. Nutr Cycl Agroecosyst 64 193-201 Fuseler K, Krekeler D, Sydow U, Cypionka H (1996) A common pathway of sulfide oxidation by sulfate-reducing bacteria. FEMS Microbiol Lett 144 129-134 Galushko AS, Schink B (2000) Oxidation of acetate through reactions of the citric acid cycle by Geobacter sulfurreducens in pure culture and in syntrophic coculture. Arch Microbiol 174 314-321... 

Oxidation under anaerobic conditions of long-chain aliphatic carboxylic acids was established in syntrophic cultures of Clostridium bryantii / Desulfovibrio sp. (Stieb and Schink 1985), Syntrophomonas sapovorans /Methanospirillum hungatei (Roy et al. 1986), and S. wolfei in coculture with H2-utilizing anaerobic bacteria (Mclnerney et al. 

There has been considerable interest in the anaerobic degradation of propionate that is a fermentation product of many complex substrates, and syntrophic associations of acetogenic and metha-nogenic bacteria have been obtained. 

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