Division plane placement in pleomorphic archaea is dynamically coupled to cell shape.

One mechanism for achieving accurate placement of the cell division machinery is via Turing patterns, where nonlinear molecular interactions spontaneously produce spatiotemporal concentration gradients. The resulting patterns are dictated by cell shape. For example, the Min system of Escherichia coli shows spatiotemporal oscillation between cell poles, leaving a mid-cell zone for division. The universality of pattern-forming mechanisms in divisome placement is currently unclear. We examined the location of the division plane in two pleomorphic archaea, Haloferax volcanii and Haloarcula japonica, and showed that it correlates with the predictions of Turing patterning. Time-lapse analysis of H. volcanii shows that divisome locations after successive rounds of division are dynamically determined by daughter cell shape. For H. volcanii, we show that the location of DNA does not influence division plane location, ruling out nucleoid occlusion. Triangular cells provide a stringent test for Turing patterning, where there is a bifurcation in division plane orientation. For the two archaea examined, most triangular cells divide as predicted by a Turing mechanism; however, in some cases multiple division planes are observed resulting in cells dividing into three viable progeny. Our results suggest that the division site placement is consistent with a Turing patterning system in these archaea.

Haloferax chudinovii sp. nov., a halophilic archaeon from Permian potassium salt deposits.

Three pigmented strains of halophilic archaea (RS75, RS77, RS79) were isolated from the monoliths of mottled sylvinite from the Verkhnekamsk salt deposit (Solikamsk, Russia). The cells were nonmotile, gram-negative, pleomorphic, disk-shaped or ovoid, 0.8-1.0 × 1.5-2.5 µm. The organism was a chemoorganotrophic obligate aerobe producing catalase and oxidase. A number of carbohydrates and carboxylic acids were used as growth substrates. Growth occurred in the presence of 7-27% NaCl (with the optimum at 15-18%), 0.02-20% KCl (0.2-1%), 0.2-16% MgCl2 (2-3%), in the temperature range from 23 to 51 °C (40-45 °C), and pH 5.5-8.0 (6.8-7.0). The membranes contained carotenoids of the bacterioruberin series. Phosphatidylglyceromethylphosphate (PGP-Me), phosphatidylglycerol (PG), sulfated diglycosyl diether (S-DGD-1) predominated among the polar lipids. The DNA G + C content was 64.0-65.0 mol %. Phylogenetic analysis of the 16S rRNA gene sequences showed high similarity of the new strains to Haloferax species: H. denitrificans (99.2%) and H. volcanii (99.1%), H. larsenii (96.9%) and H. elongans (96.6%). DNA-DNA hybridization revealed 93-95% similarity between strain RS75 and strains RS77 and RS79; the similarity levels between strain RS75 and the type strains of Haloferax denitrificans VKM B-1754(T) and Halobacterium salinarum VKM B-1769(T) were 50 and 10%, respectively. According to its phenotypic and genotypic characteristics, the organism was classified as a member of the genus Haloferax, forming a new species with the proposed name Haloferax chudinovii sp. nov. type strain is RS75(T) (=VKPM B-11279(T)).

Transfer of Halobacterium denitrificans (Tomlinson, Jahnke, and Hochstein) to the genus Haloferax as Haloferax denitrificans comb. nov.

Halobacterium denitrificans (Tomlinson, Jahnke, and Hochstein) was described at a time when the taxonomic subdivision of the family Halobacteriaceae was in a state of flux. On the basis of both biochemical and chemotaxonomic data, this organism exhibits features which indicate that it is more closely related to members of the genus Haloferax. On the basis of such criteria, we propose that Halobacterium denitrificans be reclassified as Haloferax denitrificans comb. nov. The type strain is strain ATCC 35960 (= DSM 4425).