Keywords

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Taxonomy, Historical and Current

Short Description of the Family

De.sul.far.cu.la’ce.ae. N.L. masc. n. Desulfarculus, type genus of the family; suff. -aceae, ending to denote family; N.L. fem. pl. n. Desulfarculaceae, the Desulfarculus family. The description is an emended version of the description given in Bergey´s Manual, 2nd edition (Kuever et al. 2005b, c).

The family belongs to the order Desulfarculales within the delta-Proteobacteria. The family Desulfarculaceae contains a single genus Desulfarculus (Kuever et al. 2006) which is the type genus of the family (Kuever et al. 2006). Gram-staining negative. Morphological forms are always vibrio-shaped cells. Spore formation is absent. The only member is motile by means of one or two polar flagella. Strictly anaerobic, having a respiratory type of metabolism. Fermentative metabolism was not observed. Formate and short- and long-chain fatty acids are used as electron donors. The only described species oxidizes organic substrates completely to carbon dioxide. The only member is mesophilic. The only described species is chemoorganoheterotroph and chemolithoheterotroph. Sulfate, sulfite, and thiosulfate are used as electron acceptor and reduced to sulfide. The only member has been isolated from a freshwater habitat. Similar organism might occur in brackish water and marine habitats.

Phylogenetic Structure of the Family

The phylogenetic structure of the family and its neighboring families is shown on Fig. 3.1 . The borders of the family are primarily based on the phylogenetic tree as framework and their unique properties (Physiology, chemotaxonomic markers) which are present in all members (see Table 3.1 ).

Fig. 3.1
figure 1figure 1

Phylogenetic reconstruction of the family Desulfarculaceae based on the neighbor-joining algorithm with the Jukes-Cantor correction. Sequence dataset and alignments according to the All-Species Living Tree Project release LTPs108 (Yarza et al. 2010). The tree topology was stabilized with the use of a representative set of around 750 high-quality-type strain sequences proportionally distributed among the different bacterial and archaeal phyla. In addition, a 40 % maximum frequency filter was applied to remove hypervariable positions from the alignment. Scale bar indicates estimated sequence divergence 2005

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Table 3.1 Selected characteristics of the only member of the genus Desulfarculus
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Molecular Analyses

DNA-DNA Hybridization Studies

Are absent.

Bioprinting and Ribotyping

Are absent.

MALDI-TOF

Are absent.

Genome Comparison

The complete genome sequence of the only described species of the genus Desulfarculus which is also the only member of this family which has been analyzed (Sun et al 2010). The genome of the type strain of Desulfarculus baarsii 2st14 is 3,655,731 bp long and contains 3,355 genes with 3,303 coding for proteins and 52 coding for RNA genes. The mol% G + C of the DNA is 65.7. In the genome single copies of the dissimilatory, adenylylsulfate reductase (AprBA) and the dissimilatory sulfite reduction (DsrAB) were found. The aprBA gene is similar to gram-positive aprBA genes and the Qmo complex is incomplete and consists only out of QmoAB. The QmoC is lacking which is also similar to gram-positive sulfate-reducing (e.g., Desulfotomaculum and Desulfosporosinus).

Phages

Phages might be present, but are not reported so far.

Phenotypic Analyses

The main features of the only member of the family Desulfarculaceae is listed in Table 3.1 .

All members are gram-negative vibrio. The only species is motile. All are strictly anaerobic, having a respiratory or fermentative metabolism.

The cellular fatty acid pattern of D. baarsii strain 2st14T is dominated by saturated straight chain fatty acids (43.0 % C 14:0, 9.9 % C 16:0, and 2.3 % C 18:0 ), followed by saturated iso- and anteiso-branched fatty acids (21.3 % i-C 14:0, 12.3 % ai-C 15:0, and 2.8 % i-C 15:0). A comparison of the fatty acid profiles of D. baarsii and various gram-negative sulfate reducers by cluster analysis indicated a separate position of D. baarsii (Vainshtein et al. 1992) [31], corroborating the distinct phylogenetic position of the species as shown based on the 16S rRNA sequence analysis (Fig. 3.1 ).

The dominant respiratory quinone is MK-7(H2) (Collins and Widdel 1986). Organic substrate oxidation is always complete. Typical electron donors for sulfate reduction are formate, short-chain and long-chain fatty acid, and short-chain branched fatty acids. Fermentation was never observed. Formate allows chemolithoautotrophic growth without acetate. Typical electron acceptors for growth are sulfate, sulfite, and thiosulfate.

Desulfoviridin is not present. The optimal growth is between 35 °C and 39 °C; NaCl is not required for growth.

Strains belonging to this genus might be isolated from various anoxic sediments.

Desulfarculus Kuever et al. 2006, 1VP (Effective Publication Kuever et al. 2005a, 1004)

De.sul.far’cu.lus. L. pref. de, from; L. n. sulfur, sulfur; N.L. masc. n. arculus, a small bow; N.L. masc. n. Desulfarculus, a bow-shaped sulfate-reducer.

The genus Desulfarculus contains a single validly described species. Its chemotaxonomic and physiological properties are listed in Table 3.1 .

In D. baarsii, a high activity of carbon monoxide dehydrogenase is observed, indicating the operation of the anaerobic C1-pathway (Wood-Ljungdahl pathway) for formate assimilation and CO2 fixation or complete oxidation of acetyl-CoA (Schauder et al. 1986). This is also reflected from genome data (Sun et al. 2010).

Taxonomic comment: The phylogenetic tree (Fig. 3.1 ) clearly indicates that Desulfarculus baarsii represents an isolated and deeply branching lineage. Therefore, the classification as a separate order and family is justified. This is also reflected by phylogenetic trees based on the dsrAB and aprBA genes (Zverlov et al. 2005; Meyer and Kuever 2007).

Biolog

Biolog date are not available for sulfate-reducing bacteria.

Isolation, Enrichment, and Maintenance Procedures

The only described member of the family Desulfarculaceae requires anoxic media for growth like all other sulfate-reducing bacteria. The media are prepared under specific conditions, and the addition of a reductant is required, in general sulfide to keep the medium oxygen-free. A detailed description is provided by Widdel and Bak (1992). A detailed description is provided in the genus description (Kuever et al. 2005c).

For enrichment the used electron donor should be highly selective and would have a strong influence on what kind of sulfate-reducing bacteria will grow in the medium. The most selective substrates for the isolation of Desulfarculus spp. might be long-chain fatty acids and branched short-chain fatty acids. One might succeed also with formate in the absence of acetate. As usual electron acceptor sulfate is used. All these substrates might enrich also for other sulfate-reducing bacteria belonging to other genera because there are several which have quite similar nutritional requirements.

Most sulfate-reducing bacteria of this family have been enriched using batch cultures; other options are serial dilution techniques of natural samples. For isolation in general, roll-tube techniques or deep agar serial dilution techniques are favored against plating techniques in combination with anoxic chambers (Widdel and Bak 1992; Kuever et al. 2005d).

For short-term preservation, stock cultures can be stored at 2–6 °C for 4–6 weeks. The transfer interval varies from strain to strain and depends on the tendency to lyse under suboptimal conditions. For long-term storage, cultures can be kept freeze dried, at −80 °C, or in liquid nitrogen.

Ecology

Habitat

Members of this family might be isolated from various habitats including freshwater, brackish, and marine systems. There are several clone sequences based on the 16S rRNA gene described which would fell into this family. So members of this family might be widespread, although isolates are lacking. The type strain of the genus Desulfarculus, strain 2st14, was isolated with stearate as only electron donor and sulfate as electron acceptor from anoxic sediment of a freshwater ditch close to the University of Konstanz, Germany.

Pathogenicity, Clinical Relevance

There is no pathogenic relevance known.