Evidence for two different gas vesicle proteins and genes in Halobacterium halobium.

Most halobacteria produce gas vesicles (GV). The well-characterized species Halobacterium halobium and some GV+ revertants of GV- mutants of H. halobium produce large amounts of GV which have a spindlelike shape. Most other GV+ revertants of H. halobium GV- mutants and other recently characterized halobacterial wild-type strains possess GV with a cylindrical form. The number of intact particles in the latter isolates is only 10 to 30% of that of H. halobium. Analysis of GV envelope proteins (GVPs) by electrophoresis on phenol-acetic acid-urea gels showed that the GVP of the highly efficient GV-producing strains migrated faster than the GVP of the low-GV-producing strains. The relative molecular mass of the GVP was estimated to be 19 kilodaltons (kDa) for high-producing strains (GVP-A) and 20 kDa for low-producing strains (GVP-B). Amino acid sequence analysis of the first 40 amino acids of the N-terminal parts of GVP-A and GVP-B indicated that the two proteins differed in two defined positions. GVP-B, in relation to GVP-A, had Gly-7 and Val-28 always replaced by Ser-7 and Ile-28, respectively. These data suggest that at least two different gvp genes exist in H. halobium NRL. This was directly demonstrated by hybridization experiments with gvp-specific DNA probes. A fragment of plasmid pHH1 and a chromosomal fragment of H. halobium hybridized to the probes. Only a chromosomal fragment hybridized to the same gyp probes when both chromosomal and plasmid DNAs from the low-GV-producing halobacterial wild-type strains SB3 and GN101 were examined. These findings support the assumption that GVP-A is expressed by a pHH1-associated gvp gene and GVP-B by a chromosomal gvp gene.     

Properties of the Amylase from Halobacterium halobium

Halobacterium halobium amylase had optimal activity at pH 6.4 to 6.6 in sodium beta-glycerophosphate buffer containing 0.05% NaCl at 55 C; Ca(2+) was not required. End products from amylose were maltose, maltotriose, and glucose. The amylase, which was devoid of transglucosylase activity, had a multichain attack mechanism.     

Polyadenylated RNA isolated from the archaebacterium Halobacterium halobium.

Polyadenylated [poly(A)+] RNA has been isolated from the halophilic archaebacterium Halobacterium halobium by binding, at 4 degrees C, to oligo(dT)-cellulose. H. halobium contains approximately 12 times more poly(A) per unit of RNA than does the methanogenic archaebacterium Methanococcus vannielii. The 3' poly(A) tracts in poly(A)+ RNA molecules are approximately twice as long (average length of 20 nucleotides) in H. halobium as in M. vannielii. In both archaebacterial species, poly(A)+ RNAs are unstable.     

Chemosensory responses of Halobacterium halobium.

Responses of Halobacterium halobium cells to chemical stimuli have been shown by a capillary technique. Cells were attacted by D-glucose and several amino acids and repelled by phenol. Certain chemicals, such as acetate, benzoate, indole, and NiSO4, that are known to act as repellents of Escherichia coli cells served as attractants for Halobacterium. In the presence of ethionine, sensitivity to attractants was reduced. Arsenate prevented the attraction by glucose without lowering the cellular adenosine 5'-triphosphate level. The ability for chemo-accumulation toward glucose and histidine was interfered with by the formation of photosensory systems. Light-induced motor responses and chemosensory behavior toward glucose and histidine became detectable in the late stationary growth phase only. The behavior toward acetate and indole was not connected to photobehavior in that way: both substances acted as attractants already in the late log phase. Inhibition of bacteriorhodopsin synthesis by L-nicotine allowed chemo-accumulation toward glucose and histidine already in the late logarithmic phase.     

Chromophore of sensory rhodopsin II from Halobacterium halobium.

The photoreceptor sensory rhodopsin II (sR-II) was enriched 120-fold from cell membranes of Halobacterium halobium. The final preparation yields sR-II with a specific content of 3 nmol of sR-II/mg of protein. The spectroscopic measurements were performed on the enriched photoreceptor solubilized in digitonin. In the absolute absorption spectrum of the partially purified receptor, the main peak in the visible range corresponded to sR-II with a maximum at 488 nm. Cytochromes contributed to the spectrum only in a minor band at 415 nm. The extinction coefficient of sR-II was estimated from difference spectra during bleaching with hydroxylamine to be 48,000 M-1 cm-1. The reduced chromophore displayed a pronounced fine structure which is due to the coplanarity of the retinyl residue. The isomeric composition of the chromophore from the enriched photoreceptor was determined in retinal extracts in HPLC. The dark-adapted sR-II contains 80% all-trans- and 20% 13-cis-retinal. After illumination, the ratio changed to 1:1, indicating a trans-cis isomerization during the photocycle of sR-II.     

Phase behavior of lipids from Halobacterium halobium

Mixtures of dipalmitoylphosphatidylcholine with purple membrane lipids, red membrane lipids, or total lipids of Halobacterium halobium have been studied with differential scanning calorimetry. A comparison of red and purple membrane lipids reveals no difference in their phase behavior, indicating that lipid phase behavior plays no role in the in vivo separation of red and purple membranes. The effects of variation of the salt content of the suspending solution have also been examined. Studies of the melting behavior of these mixtures as H. halobium lipid content is varied suggest that the gel to liquid-crystal transition does not occur in the lipids of H. halobium.     

Efficient transfection of the archaebacterium Halobacterium halobium.

We developed an efficient polyethylene glycol-mediated spheroplast transfection method for the extremely halophilic archaebacterium Halobacterium halobium. The 59-kilobase-pair linear phage phi H DNA molecule routinely produced between 5 X 10(6) and 2 X 10(7) transfectants per microgram of DNA. Between 0.5 and 1% of spheroplasts were transfected per microgram of luminal diameter H DNA. Under our conditions, survival and regeneration of H. halobium spheroplasts were also quite efficient, suggesting that this method will be useful for introducing other DNAs into these bacteria.     

Structure of the purple membrane from Halobacterium halobium

European Biophysics Journal -     

Purification and properties of serine protease from Halobacterium halobium.

Pure extracellular serine protease was isolated from the culture filtrate of Halobacterium halobium by bacitracin-Sepharose affinity chromatography. The enzyme activity was completely and irreversibly lost if the NaCl concentration fell below 2 M. The protease consists of one polypeptide chain with a molecular weight of 41,000. It is characteristically enriched in Asx and Glx content, whereas the level of basic amino acids in the enzyme molecule is unusually low. The protease shows a preference for leucine in the carboxylic side of the scissile bond of the substrate, cleaving the B-chain of oxidized bovine insulin only at the Leu15-Tyr16 bond and liberating p-nitroaniline from L-pyroglutamyl-L-alanyl-L-alanyl-L-leucine-p-nitroanilide.     

Photochemistry of two rhodopsinlike pigments in bacteriorhodopsin-free mutant of Halobacterium halobium.

Two photocycles due to two different pigments were found in membrane vesicles of a bacteriorhodopsin-free mutant of Halobacterium halobium. A pigment absorbing approximately 590 nm halorhodopsin (HR) underwent a faster photocycle with a phototransient at approximately 490 nm (half-time of decay, tau 1/2 = 10 ms). Another third rhodopsinlike pigment (TR) absorbing approximately 580 nm underwent a slower photocycle accompanying a phototransient absorbing below 410 nm (tau 1/2 = 0.8s). The photocycles were measured under various conditions of temperature, NaCl concentration, pH, and in the presence of cholate. All results obtained support the notion that the two photocycles are independent of each other, and the fast or the slow cycle can be abolished after these treatments. At alkaline pH, the wavelength of maximum absorbance of both pigments shifted to blue, but the magnitude of the shift of the pigment undergoing the slow photocycle was much greater than the other. The ratio of the content of the two pigments varies among bacteriorhodopsin-free mutants.     

Purification and properties of two 2-oxoacid:ferredoxin oxidoreductases from Halobacterium halobium

Pyruvate:ferredoxin oxidoreductase and 2-oxoglutarate:ferredoxin oxidoreductase were obtained from cell-free extracts of Halobacterium halobium as homogeneous proteins after ammonium sulfate precipitation, salting-out chromatography with ammonium sulfate on unsubstituted agarose, gel filtration and chromatography on hydroxyapatite. The respective molecular weights are 256000 and 248000. Both enzymes consist of two sets of non-identical subunits of Mr 86000 and 42000 in the case of the pyruvate-degrading enzyme and of 88000 and 36000 in the case of the 20 -oxogluatarate-degrading enzyme. Analyses indicate that an intact enzyme molecule contains two [4 Fe-4S]2 + (2 + , 1+) clusters and two molecules of thiamin diphosphate. Flavin nucleotides, lipoic acid and pantetheine are absent. Thus the enzymes are very similar to the 2-oxoacid:ferredoxin oxidoreductases from fermentative and photosynthetic anaerobes described previously, but are clearly different from the 2-oxoacid dehydrogenase multienzyme complexes which commonly occur in anaerobic organisms.     

Improved isolation procedures for the purple membrane of Halobacterium halobium.

Techniques for purifying teh purple membrane of Halobacterium halobium are given. This purple membrane contains a chromoprotein with a retinal prosthetic group similar to rhodopsin, the chromprotein found in the visual systems of higher invertebrates and vertebrates. The described purple membrane isolation procedures yield a highly purified preparation as determined by transmitting electron microscopy and gel electrophoresis. Critical analysis of the absorption spectra of the purple membrane was also employed to establish criteria of purity for the preparation. The visible absorption spectra of the purified purple membrane preparation in buffer was found to have a maximum at 559 nm which shifted to 567 nm on light exposure. No indication of any spectral perturbation arising from bacterioruberin-containing membrane, the major contaminant in purple membrane preparations, was found. Furthermore, the ratio of protein aromatic amino acid absorbance at 280 nm to chromophore absorbance at 567 nm was found to be 1.5 in light-exposed preparations compared to the previously reported ratio of 2.3.-3 The decrease in the value of this ratio is also indicative of an increase in the purity of the purple membrane preparation.     

Putative promoter region of rRNA operon from archaebacterium Halobacterium halobium.

The 100 bp sequence from the beginning of the 16S rRNA gene of archaebacterium Halobacterium halobium and the adjacent 800 bp upstream sequence were determined. Four long (80 bp) direct repeats were found in the region preceeding the structural gene of the 16S rRNA. These repeats are proposed to constitute the promoter region of the rRNA operon of H. halobium.     

Isolation and characterization of halorhodopsin from Halobacterium halobium

Chromoprotein of a light-driven chloride pump, halorhodopsin (HR), was isolated from Halobacterium halobium L-33, which contains HR and "slowly cycling rhodopsin-like pigment" (SR) but lacks bacteriorhodopsin (BR). The isolation was run in the presence of more than 2 M NaCl, which was required to preserve this halophilic retinal protein. Cell envelope vesicles were washed with Tween-20 to remove 80% of the proteins. The residual membranes were solubilized with 0.5% C12E9, which had little effect on the photochemical activities of HR and SR. HR was purified by passing it through a hydroxyapatite and then a phenyl-Sepharose column in 2 M NaCl and 0.5% C12E9. The absorption maximum of HR was 578 nm and the ratio of absorbance at 280 nm to 580 nm was 1.52. The apparent molecular weight of HR was 20,000 on polyacrylamide gel electrophoresis in the presence of SDS. The characteristic, bilobed CD spectrum of HR in the visible region suggested that HR exists as an oligomer in both its membrane-bound and isolated forms.