Haloquadratum walsbyi gen. nov., sp. nov., the square haloarchaeon of Walsby, isolated from saltern crystallizers in Australia and Spain

Int J Syst Evol Microbiol. 2007 Feb;57(Pt 2):387-392. doi: 10.1099/ijs.0.64690-0.


Strains C23T and HBSQ001 were isolated from solar salterns and are novel square-shaped, aerobic, extremely halophilic members of the domain Archaea and family Halobacteriaceae. Cells stained Gram-negative and grew optimally in media containing 18 % salts at around neutral pH. Mg2+ is not required. The DNA G+C content of both isolates was 46.9 mol% and DNA-DNA cross-hybridization showed a relatedness of 80 %. Their 16S rRNA gene sequences showed only 2 nucleotide differences (99.9 % identity) and phylogenetic tree reconstructions with other recognized members of the Halobacteriaceae indicated that they formed a distinct clade, with the closest relative being Halogeometricum borinquense PR 3T (91.2 % sequence identity). The major polar glycolipid of both isolates was the sulfated diglycosyl diether lipid S-DGD-1. Electron cryomicrosopy of whole cells revealed similar internal structures, such as gas vesicles and polyhydroxyalkanoate granules, but the cell wall of isolate HBSQ001 displayed a more complex S-layer compared with that of isolate C23T. The phenotypic characterization and phylogenetic data support the placement of isolates C23T and HBSQ001 in a novel species in a new genus within the Halobacteriaceae, for which we propose the name Haloquadratum walsbyi gen. nov., sp. nov. The type strain of Haloquadratum walsbyi is C23T (=JCM 12705T=DSM 16854T).

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aerobiosis
  • Australia
  • Base Composition
  • Cell Wall / ultrastructure
  • Cytoplasm / ultrastructure
  • DNA, Archaeal / chemistry
  • DNA, Archaeal / isolation & purification
  • Genes, rRNA
  • Halobacteriaceae / classification*
  • Halobacteriaceae / cytology
  • Halobacteriaceae / isolation & purification*
  • Halobacteriaceae / physiology
  • Hydrogen-Ion Concentration
  • Magnesium / metabolism
  • Molecular Sequence Data
  • Nucleic Acid Hybridization
  • Organelles / ultrastructure
  • Phospholipids / analysis
  • Phospholipids / chemistry
  • Phylogeny
  • RNA, Archaeal / genetics
  • RNA, Ribosomal, 16S / genetics
  • Salts
  • Seawater / microbiology*
  • Sequence Analysis, DNA
  • Spain
  • Water Microbiology


  • DNA, Archaeal
  • Phospholipids
  • RNA, Archaeal
  • RNA, Ribosomal, 16S
  • Salts
  • Magnesium

Associated data

  • GENBANK/AM180088
  • GENBANK/AY676200