• DOI:10.1007/978-3-642-38922-1
• Corpus ID: 43059672

The Prokaryotes

@inproceedings{Wood2014TheP,
  title={The Prokaryotes},
  author={Ann P. Wood},
  booktitle={Springer Berlin Heidelberg},
  year={2014}
}

• A. Wood
• Published in Springer Berlin Heidelberg 2014

The family Achromatiaceae (comprising the single genus Achromatium) is a group of morphologically conspicuous, single-celled, free-living, colorless sulfur-oxidizing bacteria which forms a coherent phylogenetic group within the Gammaproteobacteria. They have yet to be grown in laboratory culture, but ecophysiological measurements suggest they gain energy from sulfide oxidation and may use oxygen and/or nitrate as a terminal electron acceptor. Some Achromatium can fix inorganic carbon, but it is not clear if these are solely autotrophs as they have been shown to also incorporate carbon from acetate. In common with other large sulfur bacteria, they deposit elemental sulfur globules, but Achromatium spp. are unique among bacteria in that they precipitate intracellular calcium carbonate as intracellular inclusions. Recent taxonomic revisions indicate that this trait is ubiquitous to all Achromatium spp. The role of calcium carbonate precipitation and indeed many other aspects of the physiology of Achromatium remains, however, largely a matter of speculation without laboratory cultures. First described by Schewiakoff (1893, Über einen neuen bakteriennähnlichen Organismus des Süßwassers. Habilitationsschrift, Heidelberg) as Achromatium oxaliferum, these organisms have been consistently observed in diverse freshwater and to a lesser extent brackish and marine sediments. In such environments, and in contrast to mat and veil forming sulfur berg et al. (eds.), The Prokaryotes – Gammaproteobacteria, DOI 10.1007/978 er-Verlag Berlin Heidelberg 2014 bacteria, Achromatium communities are distributed throughout the zone of sulfate reduction. Here ‘‘free sulfide’’ may be present only in sub-micromolar concentrations. The organisms are responsive to redox changes and are able to migrate within the sediment column by a characteristic rolling jerky motion. Despite the absence of a cultured representative, the physical characteristics ofAchromatiaceae (size and calcite inclusions) have facilitated culture-independent studies of communities using molecular biological methods. These studies have provided useful insights into the phylogeny, diversity, and phenotype of these organisms and ultimately the ecological mechanisms (redox zonation, environmental selection) and physical variation which may facilitate the coexistence and distribution of different species. Taxonomy, Historical and Current Short Description of the Family A.chrom.a.ti.a’ce.ae. N.L. fem. n Achromatium type genus of the family; -aceae ending to denote a family; N.L. fem. Pl. n. Achromatiaceae the Achromatium family (Van Niel 1948). Type genus: Achromatium (Schewiakoff 1893). A.chro.ma’ti.um. Gr. Pref. a not; Gr. N. chromatium color, paint; M.L. net. N. Achromatium that which is not colored (Babenzien et al. 2005). The inability to cultivate a representative of the Achromatiaceae has been a handicap to past taxonomic classification. Nevertheless, based on distinctive morphological and behavioral characteristics (size, sulfur inclusions, presence of calcium carbonate inclusions, and observed rolling motility), members of the family have been variously named Achromatium oxaliferum (Schewiakoff 1893), Modderula hartwigi (Frenzel 1897), Achromatium gigas (Nadson 1913), Hillhousia mirabilis (West and Griffiths 1909), and Hillhousia palustris (West and Griffiths 1913). From the middle of the twentieth century onward, the Achromatium-like organisms listed above have been united in the family Achromatiaceae containing a single genus Achromatium comprising two species (Van Niel 1948). At this time the genus Achromatium included the calcium carbonate containing Achromatium oxaliferum (formerly named Achromatium Schewiakoff) and a marine species Achromatium volutans (formerly named Thiophysa volutans) which does not contain calcium carbonate inclusions (Hinze 1903). In the first edition of Bergey’s Manual of Systematic Bacteriology, the genus was placed with the non-fruiting gliding bacteria as a genus incertae sedis by virtue of its observed means of locomotion (La Rivière and Schmidt 1989). In the second edition of