Extreme Halotolerant Research Articles

The phylogeny of unicellular, extremely halotolerant cyanobacteria.

We examined the morphology, physiology, and 16S rRNA gene sequences of three culture collection strains and of ten novel isolates of unicellular cyanobacteria from hypersaline environments. The strains were morphologically diverse, with average cell widths ranging from 2.8 to 10.3 micron. There were single-celled, colonial, and baeocyte-forming strains. However, morphological traits were markedly variable with culture conditions. In contrast, all strains displayed extreme halotolerance (growing close to optimally at above 12% salinity); all were obligately marine, euryhaline, and moderately thermophilic; and all shared a suite of chemotaxonomic markers including phycobilins, carotenoids, and mycosporine-like amino acids. 16S rRNA gene sequence analysis indicated that the strains were related to each other. Sequence similarity analysis placed the strains in a monophyletic cluster (which we named the Halothece cluster) apart from all cultured or uncultured, not extremely halotolerant cyanobacteria whose 16S rRNA gene sequences are available in public nucleotide sequence databases. This represents the first case in which a phylogenetically coherent group of cyanobacteria can be defined on the basis of physiology. The Halothece cluster contained two subclusters that may be divergent at the generic level, one encompassing 12 strains (spanning 5% 16S rRNA gene sequence divergence and named the Euhalothece subcluster), and a single deep-branching isolate. Phenotypic characterization of the isolates, including morphological, physiological, and chemotaxonomic traits, did not distinguish these subclusters and only weakly suggested the existence of two separate clades, one encompassing strains of small cell size (cell width < 5 m) and another one encompassing strains of larger cell size.

A Salt-Induced 60-Kilodalton Plasma Membrane Protein Plays a Potential Role in the Extreme Halotolerance of the Alga Dunaliella.

The halotolerant alga Dunaliella salina grows in saline conditions as varied as 0.5 and 5 M NaCl, maintaining throughout this range a low intracellular ion concentration. To discover factors potentially involved in ionic homeostasis, we grew cells in media with different salinities or osmolarities and compared their protein profiles. The comparisons indicated that the amount of a 60-kD protein, p60, greatly increased with an increase in salinity and was moderately enhanced when NaCl was substituted with iso-osmotic glycerol. Cells transferred from low to high NaCl or from high glycerol to iso-osmotic NaCl media transiently ceased to grow, and resumption of growth coincided approximately with an increase in p60. The protein, extracted from a plasma membrane fraction, was purified to homogeneity. Anti-p60 antibodies cross-reacted with a 60-kD protein in Dunaliella bardawil. Immunoelectron microscopy of D. salina cell sections indicated that p60 was exclusively located in the plasma membrane. Its induction by salt, the correlation between its accumulation and growth resumption in high concentrations of salt, and its plasma membrane localization suggest the possibility that p60 could play a role in ionic homeostasis in conditions of high salinity, although different types of function could also be considered.

The Chloride Sensitivity of Dunaliella parva Enzymes

Summary The NaCl resistance of enzymes in crude extracts from the extreme halotolerant alga Dunaliella parva was investigated. Enzymes exhibit a very broad scale of sensitivity against NaCl, ranging from half maximal inhibitions at 100 mM up to the molar range. Salt resistance depends on the type of the enzyme as well as on the substrate concentrations: Enzymes with nonelectrolytes exhibit a relatively higher salt tolerance than those with anionic substrates. Salt — inactivation is caused by Cl - and not by K + or Na + . A competitive type of interaction of the Cl - anion with the anionic substrate is observed. Consequently high concentrations of anionic substrates protect enzymes in vivo against Cl - inactivation. Half maximal inhibition of enzymes from D. parva cells adapted to different salinities were not significantly different under substrate saturating conditions, but the KM-Values for the substrates increased with the salinity of the preculture.

Ultrastructure of Debaryomyces hansenii.

The ultrastructure of the extreme halotolerant yeastDebaryomyces hansenii (Zopf) van Rij was similar whether the organism was grown under normal physiological conditions or at high concentrations of NaCl (12, 20 per cent w/v). A multitude of channels often seen in association with plasma membrane and/or vacuoles occur in the cytoplasm. The vacuoles contain lipid storage material. A decrease in mitochondrial size was observed with increasing salt concentration. The ultrastructure has been discussed with respect to halotolerance.