Electron-ion equilibration in ultrafast heated graphite.

We have employed fast electrons produced by intense laser illumination to isochorically heat thermal electrons in solid density carbon to temperatures of ∼10,000 K. Using time-resolved x-ray diffraction, the temperature evolution of the lattice ions is obtained through the Debye-Waller effect, and this directly relates to the electron-ion equilibration rate. This is shown to be considerably lower than predicted from ideal plasma models. We attribute this to strong ion coupling screening the electron-ion interaction.

Lung retrieval from non-heart-beating donors: first experience with an innovative preservation strategy in a pig lung transplantation model.

OBJECTIVE: Lung transplantation is limited by the scarcity of donor organs. Lung retrieval from non-heart-beating donors (NHBD) might extend the donor pool and has been reported recently. However, no studies in NHBD exist using the novel approach of retrograde preservation with Perfadex solution. METHODS: Heparinized asystolic pigs (n = 5, 30-35 kg) were ventilated for 90 min. The lungs were retrogradely preserved with Perfadex solution and stored inflated at 4 degrees C for 3 h. Left lung transplantation in the recipient was followed by exclusion of the right lung. Results were compared to sham-operated animals. Oxygenation, hemodynamics and dynamic compliance were monitored for 4 h. Infiltration of polymorphonuclear cells (PMNs) and stereological quantification of alveolar edema was performed. Statistical analysis comprised Kruskal-Wallis and Mann-Whitney tests and ANOVA analysis with repeated measures. RESULTS: No mortality was observed. During preservation, continuous elimination of blood clots via the pulmonary artery venting site was observed. Oxygenation and compliance were similar between groups, but sham controls showed significantly lower pulmonary vascular resistance. Stereological quantification revealed higher volume fractions of intra-alveolar edema in NHBD grafts, while PMN infiltration was comparable to sham controls. CONCLUSIONS: Use of NHBD lungs results in excellent outcome after 90 min of warm ischemia followed by retrograde preservation with Perfadex solution. This novel approach can optimize lung preservation by eliminating clots from the pulmonary circulation and might clinically be considered in brain-dead organ donors who become hemodynamically unstable prior to organ harvest. Further trials with longer warm and cold ischemic periods are necessary to further elucidate this promising approach to donor pool expansion.

A p-loop motif and two basic regions in the regulatory protein GvpD are important for the repression of gas vesicle formation in the archaeon Haloferax mediterranei.

DeltaD transformants containing all 14 gvp genes of Haloferax mediterranei required for gas vesicle formation except for gvpD are gas vesicle overproducers (Vac(++)), whereas DeltaD/D transformants containing the gvpD reading frame under ferredoxin promoter control on a second construct in addition to DeltaD did not form gas vesicles (Vac(-)). The amino acid sequence of GvpD indicates three interesting regions (a putative nucleotide-binding site called the p-loop motif, and two basic regions); these were altered by mutation, and the resulting GvpD(mut) proteins tested in DeltaD/D(mut) transformants for their ability to repress gas vesicle formation. The exchange of amino acids at conserved positions in the p-loop motif resulted in Vac(++) DeltaD/D(mut) transformants, indicating that these GvpD(mut) proteins were unable to repress gas vesicle formation. In contrast, a GvpD(mut) protein with an alteration of a non-conserved proline in the p-loop region (P41A) was still able to repress. The repressing function of the various GvpD proteins was also investigated at the promoter level of the gvpA gene. This promoter is only activated during the stationary phase, depending on the transcriptional activator protein GvpE. Whereas the Vac(++) DeltaD transformants contained very high amounts of gvpA mRNA predominantly in the stationary growth phase, the amount of this transcript was significantly reduced in the Vac(-) transformants DeltaD/D and DeltaD/D(P41A). In contrast, the Vac(++) DeltaD/D(mut) transformants harbouring GvpD(mut) with mutations at conserved positions in the p-loop motif contained large amounts of gvpA mRNA already during exponential growth, suggesting that this motif is important for the GvpD repressor function during this growth phase. The GvpD mutants containing mutations in the two basic regions were mostly defective in the repressing function. The GvpD(mut) protein containing an exchange of the three arginine residues 494RRR496 to alanine residues was able to repress gas vesicle formation. No gvpA mRNA was detectable in this transformant, demonstrating that this GvpD protein was acting as a strong repressor. All these results imply that the GvpD protein is able to prevent the GvpE-mediated gvpA promoter activation, and that the p-loop motif as well as the two basic regions are important for this function.

Eight of fourteen gvp genes are sufficient for formation of gas vesicles in halophilic archaea.

The minimal number of genes required for the formation of gas vesicles in halophilic archaea has been determined. Single genes of the 14 gvp genes present in the p-vac region on plasmid pHH1 of Halobacterium salinarum (p-gvpACNO and p-gvpDEFGHIJKLM) were deleted, and the remaining genes were tested for the formation of gas vesicles in Haloferax volcanii transformants. The deletion of six gvp genes (p-gvpCN, p-gvpDE, and p-gvpHI) still enabled the production of gas vesicles in H. volcanii. The gas vesicles formed in some of these gvp gene deletion transformants were altered in shape (Delta I, Delta C) or strength (Delta H) but still functioned as flotation devices. A minimal p-vac region (minvac) containing the eight remaining genes (gvpFGJKLM-gvpAO) was constructed and tested for gas vesicle formation in H. volcanii. The minvac transformants did not form gas vesicles; however, minvac/gvpJKLM double transformants contained gas vesicles seen as light refractile bodies by phase-contrast microscopy. Transcript analyses demonstrated that minvac transformants synthesized regular amounts of gvpA mRNA, but the transcripts derived from gvpFGJKLM were mainly short and encompassed only gvpFG(J), suggesting that the gvpJKLM genes were not sufficiently expressed. Since gvpAO and gvpFGJKLM are the only gvp genes present in minvac/JKLM transformants containing gas vesicles, these gvp genes represent the minimal set required for gas vesicle formation in halophilic archaea. Homologs of six of these gvp genes are found in Anabaena flos-aquae, and homologs of all eight minimal halobacterial gvp genes are present in Bacillus megaterium and in the genome of Streptomyces coelicolor.

Bioassays for risk assessment of coal conversion products.

Traditional as well as biotechnological processing of coal leads to complex mixtures of products. Besides chemical and physical characterization, which provides the information for product application, there is a need for bioassays to monitor properties that are probably toxic, mutagenic or cancerogenic. Investigations carried out focused on the selection, adaptation and validation of bioassays for the sensitive estimation of toxic effects. Organisms like bacteria, Daphnia magna and Scenedesmus subspicatus, representing different complexities in the biosphere, were selected as test systems for ecotoxicological and mutagenicity studies. The results obtained indicate that bioassays are, in principle, suitable tools for characterization and evaluation of coal-derived substances and bioconversion products. Using coal products, coal-relevant model compounds and bioconversion products, data for risk assessment are presented.

The transcriptional activator GvpE for the halobacterial gas vesicle genes resembles a basic region leucine-zipper regulatory protein.

The GvpE protein involved in the regulation of gas vesicles synthesis in halophilic archaea has been identified as the transcriptional activator for the promoter located upstream of the gvpA gene encoding the major gas vesicle structural protein GvpA. A closer inspection of the GvpE protein sequence revealed that GvpE resembles basic leucine-zipper proteins typically involved in the gene regulation of eukarya. A molecular modelling study of the C-terminal part implied a cluster of basic amino acid residues constituting the DNA-binding site (DNAB) followed by an amphiphilic helix, suitable for the formation of a leucine-zipper structure within a GvpE dimer. The model of a GvpE dimer docked onto DNA indicated that the side-chains of the basic residues could perfectly interact with the negatively charged phosphate groups of the DNA backbone. Substitution of three basic amino acid residues of this putative DNAB by alanine and/or glutamate generated mutated GvpE proteins. None of these was able to activate the c-gvpA promoter in vivo, indicating that these basic residues are required for GvpE activity. This identification of an archaeal gene regulator displaying similarity to eukaryal regulatory proteins implies that the basic transcription machinery of eukarya and archaea are closely related, and that the regulatory proteins have evolved according to common principles.

The characterization of the nv-gvpACNOFGH gene cluster involved in gas vesicle formation in Natronobacterium vacuolatum.

The haloalkaliphilic archaeon Natronobacterium vacuolatum forms cylinder-shaped gas vesicles throughout the growth cycle when grown in media containing 15-25% NaCl. Cells cultivated in media containing 13% NaCl are, however, gas-vesicle-free. The major gas vesicle structural protein, nv-GvpA, was detected by an antiserum raised against the gas vesicles of Haloferax mediterranei; the antiserum reacted with an 8.3-kDa protein in samples containing cell extracts or purified gas vesicles of N. vacuolatum. The gene encoding nv-GvpA was isolated together with six additional gvp genes; these genes are arranged consecutively in a cluster as nv-gvpACNOFGH and are cotranscribed. Transcript analysis by primer extension revealed only one start site three nucleotides upstream of the nv-gvpA reading frame. This arrangement of gvp genes differs from that of the gas-vesicle-encoding genes in Halobacterium salinarium and Hf. mediterranei. The comparison of the deduced Gvp protein sequences indicated similarities with the respective halobacterial Gvp proteins, with GvpA exhibiting the highest degree of conservation (97-100%). The second gas vesicle structural protein, nv-GvpC, was 150-250 amino acids longer than all other halobacterial GvpC proteins and was much less conserved (48-73%). The expression of the nv-gvp genes was monitored in N. vacuolatum cells cultivated in 20 or 13% salt media. Northern and Western analyses showed that despite the lack of gas vesicles in cells grown in 13% salt medium, the gvpACNOFGH gene cluster was transcribed and GvpA protein was synthesized, suggesting that the absence of gas vesicles is not due to a lack of transcription.

Gas vesicle formation in halophilic Archaea.

Gas vesicles are intracellular, microbial flotation devices that consist of mainly one protein, GvpA. The formation of halobacterial gas vesicles occurs along a complex pathway involving 14 different gvp genes that are clustered in a genomic region termed the "vac region". Various vac regions found in Halobacterium salinarum (p-vac and c-vac), Haloferax mediterranei (mc-vac), and Natronobacterium vacuolatum (nv-vac) have been investigated. Except for the latter vac region, the arrangement of the gvp genes is identical. Single gvp genes have been mutated to study the effect on gas vesicle synthesis in transformants and to determine their possible function. Each vac region exhibits a characteristic transcription pattern, and regulatory steps have been observed at the DNA, RNA, and protein level, indicating a complex regulatory network acting during gas vesicle gene expression.

Purification and analysis of an extremely halophilic beta-galactosidase from Haloferax alicantei.

As a first step in the development of a reporter system for gene expression in halophilic archaea, a beta-galactosidase was purified 140-fold from Haloferax alicantei (previously phenon K, strain Aa2.2). An overproducing mutant was first isolated by UV mutagenesis and screening on agar plates containing X-Gal substrate. Cytoplasmic extracts of the mutant contained 25-fold higher enzyme levels than the parent. Purification of the active enzyme was greatly facilitated by the ability of sorbitol to stabilise enzyme activity in the absence of salt, which allowed conventional purification methods (e.g., ion-exchange chromatography) to be utilised. The enzyme was optimally active at 4 M NaCl and was estimated to be 180 +/- 20 kDa in size, consisting of two monomers (each 78 +/- 3 kDa). It cleaves several different beta-galactoside substrates such as ONP-Gal, X-Gal and lactulose, but not lactose, and also has beta-D-fucosidase activity. No beta-glucosidase, beta-arabinosidase or beta-xylosidase activity could be detected. The amino-acid sequence at the N-terminus and of four proteolytic products has been determined.

[Helminth fauna of red foxes (Vulpes vulpes LINNE 1758) in southern Saxony--2: Nematodes]. / Zur Helminthenfauna des Rotfuchses (Vulpes vulpes LINNE 1758) im Süden Sachsen-Anhalts--Teil 2: Nematoden.

Between January 1993 and November 1994 a total of 1300 red foxes from the administrative districts Halle and Dessau were examined for the presence of nematodes in the stomach and the small intestine. The following nematodes were found: Toxocara canis (26.5%), Toxascaris leonina (10.5%), Uncinaria stenocephala (15.9%) Ancylostoma caninum (1.7%). The search for Trichinella spp. larvae was negative in all 780 examined foxes.

Influence of salt on the transcription of the gas-vesicle genes of Haloferax mediterranei and identification of the endogenous transcriptional activator gene.

The transcription of the 14 gvp genes of the gas-vesicle-encoding mc-vac region was investigated, using RNA from 25% and 15% (w/v) salt cultures of the moderately halophilic archaeon Haloferax mediterranei. Transcription occurred only from two promoters, located in front of the mc-gvpA and mc-gvpD genes. In both cultures transcripts spanning the entire mc-gvpDEFGHIJKLM transcription unit were formed only during the exponential growth phase. Amounts of these transcripts were larger in the 25% salt culture, in which the 2.0 kb mc-gvpD transcripts were also synthesized during the stationary phase. The levels of the mc-gvpD transcripts and of the 324 nt mc-gvpA mRNA increased in parallel during the stationary phase of the 25% salt culture. Only under these conditions were mRNAs spanning the entire mc-gvpACNO transcription unit observed, and gas-vesicles were formed. Investigation of the influence of the mc-gvpDE genes on both mc-vac promoters in transformants revealed that by themselves they were nearly inactive. The addition of mc-gvpE, however, resulted in a high level of constitutively produced mc-gvpA and mc-gvpD mRNA, indicating a transcriptional activator function for the mc-gvpE product.

Transcript analysis of the c-vac region and differential synthesis of the two regulatory gas vesicle proteins GvpD and GvpE in Halobacterium salinarium PHH4.

Halobacterium salinarium PHH4 synthesizes gas vesicles in the stationary growth phase by the expression of 14 gyp genes arranged in two clusters. The chromosomal gvpACNO (c-gvpACNO) gene cluster (encoding the major structural gas vesicle protein GvpA and the minor structural protein GvpC was transcribed as three mRNA species starting at one promoter during the stationary phase of growth. The second gene cluster, c-gvpDEFGHIKLM), was transcribed during all stages of growth as a relatively unstable, single mRNA with a maximal length of 6 kb. In addition, a 1.7-kb c-gvpD transcript was synthesized during stationary growth starting at the same promotor as that of the cgvpDEFGHIJKLM mRNA. The expression of the first two genes located in this unit (c-gvpD and c-gvpE) was also monitored by Western blot (immunoblot) analyses using antisera raised against these proteins synthesized in Escherichia coli. While the cGvpD protein was present only during early exponential growth and disappeared during gas vesicle formation, the cGvpE protein was present during cGvpA and gas vesicle synthesis in the early stationary phase of growth. Previous data indicated that cGvpD is involved in repression of gas vesicle formation, whereas cGvpE is a transcriptional activator for the c-gvpA promoter. The appearance of both proteins during the growth cycle is in line with the functions of these proteins in gas vesicle synthesis. The mechanism of the differential translation of cGvpD and cGvpE from the c-gvpDEFGHIJKLM rnRNA still has to be elucidated, but antisense RNAs complementary to the 5' terminus as well as the 3' portion of the c-gvpD mRNA might be involved in this regulation. Such RNAs occurred during early stationary growth when the cGvpD protein level decreased and may possibly inhibit the translation of the c-gvpD mRNA.

Functional studies of the gvpACNO operon of Halobacterium salinarium reveal that the GvpC protein shapes gas vesicles.

Gas vesicle (Vac) synthesis in Halobacterium salinarium PHH1 involves the expression of the plasmid pHH1-encoded vac (p-vac) region consisting of 14 different gvp genes that are arranged in two clusters, p-gvpACNO and, oriented in the direction opposite to that of gvpA, p-gvpDEFGHIJKLM. The p-gvpACNO region was analyzed at the transcriptional and functional levels in H. salinarium and in Haloferax volcanii transformants containing subfragments of the p-vac region. The p-gvpACNO genes were transcribed as several mRNAs: the 270-nucleotide (nt) p-gvpA transcript, encoding the major structural protein, occurred in large amounts, and minor amounts of three different readthrough transcripts (p-gvpACN, and p-gvpACNO mRNA) were found. In addition, the p-gvpO gene gave rise to two separate mRNA species: a 550-nt mRNA starting at the ATG and spanning the entire reading frame and a 420-nt RNA encompassing the second half of the p-gvpO gene. The requirement of p-gvpC, p-gvpN, and p-gvpO gene expression for gas vesicle synthesis was assessed by transformation experiments using the VAC- species Haloferax volcanii as the recipient. A delta C transformant, harboring the p-vac region with a deletion of the p-gvpC gene, produced large amounts of irregularly shaped gas vesicles. A shape-forming function of p-GvpC was demonstrated by complementation of the delta C transformant with the p-gvpC gene, resulting in wild-type-shaped gas vesicles. In the delta N transformant, the level of gas vesicle synthesis was very low, indicating that the p-GvpN protein is not required for gas vesicle assembly but may enhance gas vesicle synthesis. The p-gvpN deletion did not affect accumulation of p-gvpACO mRNA but reduced the separate p-gvpO transcription. The delta O transformant was Vac- and had a strongly decreased level of p-gvpACN mRNAs, demonstrating that the p-GvpO protein is required for gas vesicle synthesis and may affect transcription of this DNA region.

Liver microsomal levels of cytochrome P450IA1 as biomarker for exposure and bioavailability of soil-bound polycyclic aromatic hydrocarbons.

The bioavailability of soil-bound polycyclic aromatic hydrocarbons (PAHs) for mammalian species was studied with rats fed with a diet containing contaminated soil preparations. The extent of cytochrome P450IA1 (CYP1A1) induction in the liver correlated with the amount of 5- and 6-ring PAHs in the soil samples but not with the total PAH content. Other cytochromes P450 were much less affected by the soil-contaminants. The highest induction of CYP1A1 was obtained with a sample containing 274 mg 5- and 6-ring PAH/kg soil, resulting in a nearly 360-fold increase in the ethoxyresorufin deethylase (EROD) activity. In a semilogarithmic plot, a linear correlation was found between the 5- and 6-ring PAH concentration in the soil and the microsomal CYP1A1 content. As a model for the action of intestinal fluids, soil samples were extracted by bile acid solution. In these experiments, the selectivity in the solubilization of individual PAHs parallels that of toluene extraction, although the yield is lower than the latter and varies with the soil sample. The bioavailability of PAHs for microorganisms, but not for mammals, was shown to be considerably reduced in the presence of high total organic carbon (TOC) values of the soil samples. This may have implications for decontamination strategies, diminishing the effectiveness of biological decontamination in cases with high TOC values. The data suggest that CYP1A1 induction in rats is a parameter that may be useful in risk assessments of contaminated soils for mammalian species.

Complementation studies with the gas vesicle-encoding p-vac region of Halobacterium salinarium PHH1 reveal a regulatory role for the p-gvpDE genes.

Gas-vesicle (Vac) synthesis in Halobacterium salinarium PHH1 involves the expression of the p-vac region consisting of 14 different gvp genes that are arranged in two clusters: p-gvpACNO and, oppositely oriented, p-gvpDEFGHIJKLM. The latter cluster of genes is transcribed as two units: p-gvpDE and p-gvpF-M. The 5'-terminus of the p-gvpF-M mRNA was located 169 nucleotides upstream of p-gvpF within p-gvpE. The p-gvpG and p-gvpK gene was expressed in Escherichia coli and antibodies to proteins obtained were raised in rabbits. Both proteins could be detected in halobacterial cell lysates; in gas-vesicle preparations, however, neither GvpG nor GvpK could be found. The requirement for single p-gvp gene expression for gas-vesicle synthesis was determined by transformation experiments using the Vac- species Haloferax volcanii as recipient. Construct delta A containing all p-gvp genes except for p-gvpA, encoding the major gas-vesicle structural protein, produced Vac- transformants, but the addition of p-gvpA on a second vector restored gas-vesicle synthesis to wild-type level (Vac++). Similarly, double transformants containing p-gvpD-M plus p-gvpACNO, or p-gvpG-M (fused to the promoter of the halobacterial ferredoxin gene for expression) plus p-gvpFED-ACNO were Vac++. Transformants containing the p-vac region either lacking gvpA, gvpF, or gvpGHI were Vac-, indicating the absolute requirement of these gvp genes (or at least one in the case of gvpGHI) for gas-vesicle formation. Double transformants containing the constructs p-gvpF-M plus p-gvpACNO (delta DE) accumulated gas vesicles (Vac+) but synthesized fewer than the wild type, showing that the p-gvpDE genes are not necessary for gas-vesicle assembly. A repressor function affecting the synthesis of the p-gvpF-M mRNA could be suggested for p-gvpD and the 5'-region of its mRNA.

Analysis of the halobacterial plasmid pHK2 minimal replicon.

The pMDS series of cloning vectors developed for use in halophilic archaea have utilized a 10.5-kb plasmid, pHK2, from Haloferax sp. Aa2.2. The minimal replicon of pHK2 has now been determined (3359 bp) and completely sequenced. No significant sequence similarity was found between the pHK2 subfragment and plasmid pHV2 from the closely related H. volcanii. However, a long open reading frame (ORF), named rep, was identified which encodes a putative protein with approx. 30% sequence identity to ORFs within plasmids pGRB1, pHGN1 and pHSB1 from Halobacterium sp. All these putative Rep proteins contain sequence motifs conserved in bacterial plasmids and phage genomes known to replicate via a rolling-circle mechanism.

Improved shuttle vectors for Haloferax volcanii including a dual-resistance plasmid.

Two new Haloferax-Escherichia shuttle vectors are described, pMDS20 and pMLH3. These vectors contain the E. coli ColE1 plasmid ori region and ampicillin-resistance(ApR)-conferring bla gene, and the Haloferax pHK2 replicon region and novobiocin-resistance(NbR)-encoding gyrB gene, enabling maintenance and selection in both hosts. Plasmid pMLH3 has, in addition, a H. volcanii mevinolin-resistance (MvR) determinant and restriction sites allowing insertional inactivation of either marker, to facilitate the identification of Haloferax transformants harbouring cloned sequences. Sequencing of gyrA, within the NbR determinant, and the pHK2 ori region has been completed so the complete sequence of both pMDS20 and pMLH3 is now known.

Analysis of gas vesicle gene expression in Haloferax mediterranei reveals that GvpA and GvpC are both gas vesicle structural proteins.

Gas vesicle synthesis in Haloferax mediterranei involves several gene products encoded by a 9.4-kilobase pair DNA region (mc-vac region) that contains 13 genes in addition to gvpA encoding the major structural gas vesicle protein. The expression of part of this region, encompassing the genes gvpA, gvpC, gvpN, and gvpO was investigated. These genes are transcribed from a common promoter located upstream of gvpA. Transcripts of 0.34 (gvpA only), 1.8 (gvpA/C), 2.4 (gvpA/C/N) and 3 kilobases (gvpA/C/N/O) were observed, with the gvpA transcript being the predominant mRNA species. The majority of the mRNA formed terminates 64 base pairs downstream of gvpA at the cytosine of the sequence 5' TTTTTC 3'. The synthesis of the GvpA and GvpC proteins was investigated by Western analyses. An antiserum raised against isolated gas vesicles of Hf. mediterranei detects, in addition to gas vesicle fragments, the GvpA protein of the M(r) of approximately 8,000 in lysates derived from different halobacteria or from Escherichia coli expressing gvpA. In samples containing isolated gas vesicles, mainly partially disaggregated gas vesicle fragments hybridize, but a minor amount of monomeric GvpA is also seen. For the detection of the GvpC protein, two versions of the gvpC gene (full length and gvp delta C lacking the 3' part encoding the acidic C terminus) were expressed in E. coli, and the resulting proteins were purified. The two antisera raised against these GvpC versions indicate the expression of gvpC in different halobacteria. By Western analysis, GvpC is also detectable in samples containing isolated gas vesicles demonstrating that GvpC is a second, but minor, gas vesicle structural protein.

The fdx gene encoding the [2Fe--2S] ferredoxin of Halobacterium salinarium (H. halobium).

The gene encoding the [2Fe--2S] ferredoxin (fdx gene) was isolated from Halobacterium salinarium using two oligonucleotides deduced from the ferredoxin sequence as probes. Cosmid DNAs exhibiting hybridization were isolated, the fdx gene was localized to smaller subfragments and the nucleotide sequence determined. The 390 bp coding sequence is located in the halobacterial FI-DNA and transcribed as a 440 nucleotide mRNA. S1 mapping indicated that the 5' terminus of the mRNA maps immediately upstream of the ATG start codon. The promoter box A, centred around position -25 (5' AC-TATG 3'), and box B (TG) elements at the start of the transcript resemble the sequences of a typical archaeal promoter. The restriction pattern of an approximately 50 kb region surrounding the fdx gene is conserved in various Halobacterium species. The halobacterial ferredoxin and the major gas vesicle protein GvpA exhibit up to 70% similarity to their respective counterparts in cyanobacteria suggesting lateral gene transfer between the organisms. These similarities prompted a more detailed investigation of the relative positions of the genes in the halobacterial genome.