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Archives of Microbiology (v.173, #5-6)

Membrane targeting and translocation of bacterial hydrogenases by Long-Fei Wu; Angélique Chanal; Agnès Rodrigue (pp. 319-324).

Periplasmic or membrane-bound bacterial hydrogenases are generally composed of a small subunit and a large subunit. The small subunit contains a peculiar N-terminal twin-arginine signal peptide, whereas the large subunit lacks any known targeting signal for export. Genetic and biochemistry data support the assumption that the large subunit is cotranslocated with the small subunit across the cytoplasmic membrane. Indeed, the signal peptide carried by the small subunit directs both the small and the large subunits to the recently identified Mtt/Tat pathway, independently of the Sec machinery. In addition, the twin-arginine signal peptide of hydrogenase is capable of directing protein import into the thylakoidal lumen of chloroplasts via the homologous ΔpH-driven pathway, which is independent of the Sec machinery. Therefore, the translocation of hydrogenase shares characteristics with the ΔpH-driven import pathway in terms of Sec-independence and requirement for the twin-arginine signal peptide, and with protein import into peroxisomes in a "piggyback" fashion.

Keywords: Hydrogenase Metalloenzyme Folding Enzyme complex Signal peptide Twin-arginine Membrane targeting Cotranslocation Sec system Mtt/Tat system

Molecular biology and regulation of methane monooxygenase by J. Colin Murrell; Bettina Gilbert; Ian R. McDonald (pp. 325-332).

Methanotrophs are ubiquitous in the environment and play an important role in mitigating global warming due to methane. They are also potentially interesting for industrial applications such as production of bulk chemicals or bioremediation. The first step in the oxidation of methane is the conversion to methanol by methane monooxygenase, the key enzyme, which exists in two forms: the cytoplasmic, soluble methane monooxygenase (sMMO) and the membrane-bound, particulate methane monooxygenase (pMMO). This paper reviews the biochemistry and molecular biology of both forms of MMO. In the past few years there have been many exciting new findings. sMMO components have been expressed in heterologous and homologous hosts. The pMMO has been purified and biochemically studied in some detail and the genes encoding the pMMO have been sequenced. Copper ions have been shown to play a key role in regulating the expression of both MMO enzyme complexes. We also present a model for copper regulation based on results from Northern analysis, primer-extensions and new sequence data, and raise a number of unanswered questions for future studies.

Keywords: Methanotroph Methane oxidation Methane monooxygenase genes Regulation

The bidirectional hydrogenase of Synechocystis sp. PCC 6803 works as an electron valve during photosynthesis by Jens Appel; Saranya Phunpruch; Klaus Steinmüller; Rüdiger Schulz (pp. 333-338).

The activity of the bidirectional hydrogenase of the cyanobacterium Synechocystis sp. PCC 6803 was found not to be regulated in parallel to respiration but to photosynthesis. A mutant with a deletion in the large hydrogenase subunit gene (hoxH), which contains the active site, was impaired in the oxidation of photosystem I (PSI) when illuminated with light, which excites either PSI alone or both photosystems. The fluorescence of photosystem II (PSII) of this mutant was higher than that of wild-type cells. The transcript level of the photosynthetic genes psbA, psaA and petB was found to be different in the hydrogenase-free mutant cells compared to wild-type cells, which indicates that the hydrogenase has an effect on the regulation of these genes. Collectively, these results suggest that the bidirectional hydrogenase functions as a valve for low-potential electrons generated during the light reaction of photosynthesis, thus preventing a slowing down of electron transport. This conclusion is supported by growth curves demonstrating that the mutant cells need more time to adapt to changing light intensities. Investigations of the wild-type and ΔhoxH strains strongly suggest that Synechocystis contains only the bidirectional hydrogenase, which seems to be essentially insensitive to oxygen.

Keywords: Hydrogen metabolism hoxH Photosynthesis Respiration Electron transport Complex I

Chemical analysis of processing of spiralin, the major lipoprotein of Spiroplasma melliferum by Michel Le Hénaff; Catherine Fontenelle (pp. 339-345).

The plasma membrane of Spiroplasma melliferum contains a major membrane-associated lipoprotein called spiralin. In this study, the processing pathway of spiralin was investigated by chemical analysis of the purified protein and by using [³⁵S]cysteine, [³⁵S]methionine, [¹⁴C]myristic acid (¹⁴C-14:0), [¹⁴C]palmitic acid (¹⁴C-16:0), and globomycin. SDS-PAGE analysis of membrane proteins showed the leader peptide cleavage of prospiralin and provided evidence for an apparent selectivity in the acylation: the unprocessed protein was labelled with ¹⁴C-16:0 only (O-ester-linked acyl chains), and the mature form with both ¹⁴C-labelled fatty acids (O-ester-linked + amide-linked chains). Chemical analysis of the purified protein revealed that spiralin contains S-glycerylcysteine and is covalently modified with two O-ester-linked acyl chains and one amide-linked fatty acid chain. However, a specific selectivity in the O- and the N-acylations was not confirmed; palmitate and stearate were the major components. The amounts of O-ester- and amide-linked acyl chains, the resistance to Edman degradation and the presence of S-glycerylcysteine together indicate that spiralin is a "classical" lipoprotein (i.e. is triacylated) and is probably processed by a mechanism similar to that described for gram-negative eubacteria. On the basis of these findings, a biogenesis pathway for spiralin is proposed.

Keywords: Mollicutes Spiroplasmas Spiralin Fatty acids Signal peptide S-glycerylcysteine Lipoprotein

Molecular analysis of an outer membrane protein, MopB, of Methylococcus capsulatus (Bath) and structural comparisons with proteins of the OmpA family by Anne Fjellbirkeland; Vahid Bemanian; Ian R. McDonald; J. Colin Murrell; Harald B. Jensen (pp. 346-351).

The gene encoding a major outer membrane protein (MopB) of the methanotroph Methylococcus capsulatus (Bath) was cloned and sequenced. The cloned DNA contained an open reading frame of 1044 bp coding for a 348-amino-acid polypeptide with a 21-amino-acid leader peptide. Comparative sequence analysis of the predicted amino acid sequence revealed that the C-terminal part of MopB possessed sequences that are conserved in the OmpA family of proteins. The N-terminal half of the protein had no significant sequence similarity to other proteins in the databases, but the predicted secondary structure showed stretches of amphipathic β-strands typical of transmembrane segments of outer membrane proteins. A region with four cysteines similar to the cysteine-encompassing region of the OprF of Pseudomonas aeruginosa was found toward the C-terminal part of MopB. Results from whole-cell labeling with the fluorescent thiol-reacting reagent 5-iodoacetamidofluorescein indicated a surface-exposed location for these cysteines. A probe consisting of the 3′-end of the mopB gene hybridized to the type I methanotroph Methylomonas methanica S1 in Southern blots containing DNA from nine methanotrophic strains representing six different genera.

Keywords: Methanotroph Methylococcus capsulatus Outer membrane protein OprF protein OmpA protein

Growth phase and metal-dependent regulation of the dpsA gene in Synechococcus sp. strain PCC 7942 by Aparna Sen; Kshitij Dwivedi; Kathryn A. Rice; George S. Bullerjahn (pp. 352-357).

The Synechococcus sp. strain PCC 7942 dpsA gene encodes a stress-inducible DNA-binding protein whose transcription increases in the stationary phase. Such transcription is likely under the control of an alternative sigma factor. Our current work indicated that dpsA transcription is also important under metal-ion limitation, because dpsA mRNA levels increased 12-fold under low-iron conditions, and that dpsA function is essential for growth under iron-limiting conditions. Promoter activity of the dpsA–promoter–lacZ reporter gene constructs implied that a region of dyad symmetry centered 28 nucleotides from the transcription start is required for metal-dependent repression, as judged by the level of lacZ induction following treatment of cultures with the chelator 2,2′-dipyridyl. This potential operator sequence is distinct from the site recognized by the cyanobacterial Fur repressor homologue. No other nutrient stresses (nitrogen, sulfur, phosphorus) yielded the high level of induction seen following chelator treatment. These studies suggest that there may be more than one class of metal-dependent repressor in cyanobacteria.

Keywords: Sigma factor Iron limitation Fur repressor Nutrient stress Promoter Synechococcus

Cellular localization and metabolic function of n-butylamine-induced amine oxidases in the fungus Aspergillus niger AKU 3302 by Ivo Frébort; Shuhei Tanaka; Kazunobu Matsushita; Osao Adachi (pp. 358-365).

Using transmission electron microscopy, the amine oxidase activity in Aspergillus niger AKU 3302 was localized to the outer side of the cell wall but not inside the cell using the cerium perhydroxide deposition method. The presence of cerium in the deposit was confirmed by energy-dispersive microanalysis of X-rays. Interestingly, immunocytochemical localization using gold labeling with a specific antibody indicated the presence of amine oxidase protein inside the cell wall and not only on the outer surface. Besides labeling of the cell wall, a high level of labeling was also observed inside the cell in what seemed to be secretory vesicle structures. It is proposed that the highly active amine oxidase AO-I is located in the cell wall and serves primarily as a detoxifying agent, preventing amines from entering and damaging the cell. The amine oxidation exhibits an interesting spatial orientation involving a release of toxic hydrogen peroxide into the extracellular space. The inactive amine oxidase protein located inside the cell is most probably the amine oxidase AO-II, found in cell homogenates. It is also likely that the less active AO-II is an improperly folded precursor of AO-I, which acquired low-level activity after cell homogenization in the presence of Cu(II) and oxygen due to autooxidative formation of topaquinone.

Keywords: Amine oxidase Aspergillus niger Localization Electron microscopy

Regulation of nitrogenase activity in Rhodobacter capsulatus under dark microoxic conditions by Alexander F. Yakunin; Patrick C. Hallenbeck (pp. 366-372).

Rhodobacter capsulatus modulates its in vivo nitrogenase activity in the light in response to the addition of NH₄ ⁺ in a variety of ways: with ADP-ribosylation of the Fe-protein of nitrogenase, with a switch-off response that is independent of ADP-ribosylation, and with a "magnitude response." In the light, these responses are differentially shown by cultures that differ in the degree of their nitrogen limitation. Here we examined the response of these culture types to the addition of NH₄ ⁺ under dark, microoxic conditions and found that all three responses can be observed under these conditions. However, the magnitude response was much more sensitive to the ammonium concentration, and the ADP-ribosylation response correlated only poorly with activity changes, similar to results obtained in the light. In contrast to previous reports, Fe-protein was not ADP-ribosylated in response to the presence of oxygen.

Keywords: Nitrogenase regulation Nitrogenase inhibition Photosynthetic bacteria Nitrogenase modification

Effect of metal complexation on the bioavailability of nitrilotriacetic acid to Chelatobacter heintzii ATCC 29600 by Victoria E. White; Christopher J. Knowles (pp. 373-382).

Many polluted sites contain a mixture of organics and heavy metals. Nitrilotriacetic acid has been chosen as a model organic compound to study the effect of metal binding on organic bioavailability and degradation of organics. The effect of varying the ratio of metal to nitrilotriacetic acid on its utilisation has been examined using the gram-negative bacterium Chelatobacter heintzii ATCC 29600. The following parameters of substrate utilisation were examined: growth, degradation, respiration, mineralisation and nitrilotriacetic acid uptake. Complexation of nitrilotriacetic acid by Cu(II), Ni(II), Co(II) and Zn(II) prevented utilisation of nitrilotriacetic acid by C. heintzii; complexation to Fe(III) or Mn(II) did not. The pattern of inhibition was consistent with a 1:1 stoichiometry of metal binding to nitrilotriacetic acid. Inhibition was not due to metal ion toxicity, but was a result of metal–nitrilotriacetic acid complexes being recalcitrant to degradation. In addition, the effect of complexing (phosphate) and non-complexing (PIPES) buffers on bioavailability was examined; Co and Zn prevented degradation of nitrilotriacetic acid in PIPES buffer, but not in phosphate buffer. This was due to the removal of Co and Zn from solution by phosphate precipitation, leaving nitrilotriacetic acid uncomplexed. The results demonstrated that metal–organic complexation can alter the bioavailability of organic pollutants and may also modulate the toxicity of heavy metals.

Keywords: Bioavailability Complexation Chelation Speciation Nitrilotriacetic acid Metals Biodegradation

Analysis of promoter sequences from Lactobacillus and Lactococcus and their activity in several Lactobacillus species by Andrea McCracken; Mark S. Turner; Phil Giffard; Louise M. Hafner; Peter Timms (pp. 383-389).

Promoter-active fragments were isolated from the genome of the probiotic organism Lactobacillus rhamnosus strain GG using the promoter-probe vector pNZ272. These promoter elements, together with a promoter fragment isolated from the vaginal strain Lactobacillus fermentum BR11 and two previously defined promoters (Lactococcus lactis lacA and Lactobacillus acidophilus ATCC 4356 slpA), were introduced into three strains of Lactobacillus. Primer-extension analysis was used to map the transcriptional start site for each promoter. All promoter fragments tested were functional in each of the three lactobacilli and a purine residue was used to initiate transcription in most cases. The promoter elements encompassed a 52- to 1140-fold range in promoter activity depending on the host strain. Lactobacillus promoters were further examined by surveying previously mapped sequences for conserved base positions. The Lactobacillus hexamer regions (–35: TTgaca and –10: TAtAAT) closely resembled those of Escherichia coli and Bacillus subtilis, with the highest degree of agreement at the –10 hexamer. The TG dinucleotide upstream of the –10 hexamer was conserved in 26% of Lactobacillus promoters studied, but conservation rates differed between species. The region upstream of the –35 hexamer of Lactobacillus promoters showed conservation with the bacterial UP element.

Keywords: Lactobacillus Promoter Consensus sequence Gene expression

Menaquinol oxidase activity and primary structure of cytochrome bd from the amino-acid fermenting bacterium Corynebacterium glutamicum by Kuniichiro Kusumoto; Motoyuki Sakiyama; Junshi Sakamoto; Shunske Noguchi; Nobuhito Sone (pp. 390-397).

Cytochrome d was spectroscopically detected in membrane fractions of the amino-acid-fermenting, high-G+C gram-positive bacterium Corynebacterium glutamicum. Inhibition of NADH oxidase activity in the membranes by cyanide suggested that the main terminal respiratory oxidase during the stationary phase was a type of cytochrome bd. Cytochrome bd-type quinol oxidase, purified from the membranes, was composed of two subunits. Its reduced form showed absorption peaks at 627, 595, and 560 nm, which were due to haem d, high-spin protohaem, and low-spin protohaem, respectively. The air-oxidised form showed a peak at 645 nm, which might be due to oxygenated ferrous haem d. The spectral features and the size of subunit I are more similar to the properties of cytochromes bd from Proteobacteria, such as Escherichia coli, than to those of cytochrome bd from low-G+C gram-positive bacteria, such as Bacillus stearothermophilus. The menaquinol oxidase acitivity of the purified cytochrome bd was low, but was enhanced about fivefold by pre-incubating the enzyme with menaquinones. The order of effectiveness of quinols as oxidase substrates was clearly different from that of quinones as the activators of enzyme activity. Furthermore, activation was destroyed by ultraviolet irradiation of the pre-incubated enzyme and then restored by a second incubation with menaquinone. These results indicate that the enzymatic properties of this new oxidase are more similar to the properties of cytochromes bd from low-G+C gram-positive bacterial than to those of proteobacterial counterparts. They also suggest that the enzyme has a second quinone-binding site essential for full activity, in addition to the active centre for substrate oxidation. By using probes based on partial peptide sequences of the subunits, the genes for the two subunits of C. glutamicum cytochrome bd were cloned. The deduced amino acid sequence demonstrated that subunit I lacks the C-terminal half of the Q loop and that the primary structure of C. glutamicum cytochrome bd is more similar to that of other gram-positive bacteria than to proteobacterial cytochromes bd.

Keywords: bd-Type quinol oxidase Brevibacterium flavum Cytochrome d Glutamate fermentation Gram-positive bacteria Menaquinone

CO₂-dependent fermentation of phenol to acetate, butyrate and benzoate by an anaerobic, pasteurised culture by Anna Karlsson; Jörgen Ejlertsson; Bo H. Svensson (pp. 398-402).

Fermentative degradation of phenol was studied using a non-methanogenic, pasteurised enrichment culture containing two morphologically different bacteria. Phenol was fermented to benzoate, acetate and butyrate and their relative occurrence depended on the concentration of hydrogen. Proportionately more benzoate was formed with high initial levels of H₂. The influence of P_H2 on the fermentation pattern was studied both in dense cell suspensions and in growing cultures by addition of hydrogen. An increase in growth yield (OD₅₇₈) was observed, compared to controls, as a consequence of phenol degradation; however, the increase was less in H₂-amended treatments, in which most of the phenol ended up as benzoate. The degradation of phenol in the dense cell suspension experiments was dependent on CO₂. Benzoate was not degraded when added as a substrate to the growing culture. This is, to our knowledge, the first report concerning the fermentative degradation of phenol to non-aromatic products.

Keywords: Phenol fermentation Reductive dehydroxylation Hydrogen partial pressure Ring cleavage

Stigmatella aurantiaca Sg a15 carries genes encoding type I and type II 3-deoxy-d-arabino-heptulosonate-7-phosphate synthases: involvement of a type II synthase in aurachin biosynthesis by Barbara Silakowski; Brigitte Kunze; Rolf Müller (pp. 403-411).

3-Deoxy-d-arabino-heptulosonate-7-phosphate (DAHP) synthases catalyse the first step of the shikimate pathway. Two unrelated DAHP synthase types have been described in plants and bacteria. Two type II (aroA _A2 and aroA _A5) and one type I DAHP synthase gene (aroA ₀₀₁) were identified from the myxobacterium Stigmatella aurantiaca Sg a15. Inactivation of aroA _A5 leads to a mutant that is impaired in the biosynthesis of aurachins, which are electron transport inhibitors and contain an anthranilate moiety. Feeding of anthranilic acid to the mutant culture restores production of aurachins. Inactivation of aroA _A2 and aroA ₀₀₁ does not impair production of aurachins or other known secondary metabolites of S. aurantiaca Sg a15.

Keywords: Myxobacteria Stigmatella aurantiaca Aurachin Secondary metabolism 3-Deoxy-d-arabino-heptulosonate-7-phosphate synthases

phrA, the major photoreactivating factor in the cyanobacterium Synechocystis sp. strain PCC 6803 codes for a cyclobutane-pyrimidine-dimer-specific DNA photolyase by Wing-On Ng; Rodolfo Zentella; Yinsheng Wang; John-Stephen A. Taylor; Himadri B. Pakrasi (pp. 412-417).

A new broad-host-range plasmid, pSL1211, was constructed for the over-expression of genes in Synechocystis sp. strain PCC 6803. The plasmid was derived from RSF1010 and an Escherichia coli over-expression plasmid, pTrcHisC. Over-expressed protein is made with a removable N-terminal histidine tag. The plasmid was used to over-express the phrA gene and purify the gene product from Synechocystis sp. strain PCC 6803. PhrA is the major ultraviolet-light-resistant factor in the cyanobacterium. The purified PhrA protein exhibited an optical absorption spectrum similar to that of the cyclobutane pyrimidine dimer (CPD) DNA photolyase from Synechococcus sp. strain PCC 6301 (Anacystis nidulans). Mass spectrometry analysis of PhrA indicated that the protein contains 8-hydroxy-5-deazariboflavin and flavin adenine dinucleotide (FADH₂) as cofactors. PhrA repairs only cyclobutane pyrimidine dimer but not pyrimidine (6-4) pyrimidinone photoproducts. On the basis of these results, the PhrA protein is classified as a class I, HDF-type, CPD DNA photolyase.

Keywords: Synechocystis sp. strain PCC 6803 phrA DNA photolyase Cyclobutane pyrimidine dimer Over-expression plasmid pSL1211

Carotenoids of an Antarctic psychrotolerant bacterium, Sphingobacterium antarcticus, and a mesophilic bacterium, Sphingobacterium multivorum by Medicharla V. Jagannadham; Madhab K. Chattopadhyay; Chilukuri Subbalakshmi; Mariappanadar Vairamani; Kuthirummal Narayanan; Chintalagiri Mohan Rao; Sisinthy Shivaji (pp. 418-424).

The major carotenoid pigments of an Antarctic psychrotolerant bacterium, Sphingobacterium antarcticus, and a mesophilic bacterium, Sphingobacterium multivorum, were identified as zeaxanthin, β-cryptoxanthin, and β-carotene. Analysis was based on ultraviolet-visible spectroscopy, mass spectroscopy, and reversed-phase HPLC. Photoacoustic spectroscopy of intact bacterial cells revealed that the bulk of the pigments in S. antarcticus and S. multivorum was associated with the cell membrane. In vitro studies with synthetic membranes of phosphatidylcholine demonstrated that the major pigment was bound to the membranes and decreased their fluidity. The relative amounts of polar pigments were higher in cells grown at 5 °C than in cells grown at 25 °C. In the mesophilic strain, the synthesis of polar carotenoids was quantitatively less than that of the psychrotolerant strain.

Keywords: Carotenoids Antarctica Psychrotolerant bacterium Membrane interaction

Dimethylsulfone as a growth substrate for novel methylotrophic species of Hyphomicrobium and Arthrobacter by Elena Borodina; Donovan P. Kelly; Frederick A. Rainey; Naomi L. Ward-Rainey; Ann P. Wood (pp. 425-437).

Dimethylsulfone is a major product of the chemical oxidation in the atmosphere of the principal biogenic sulfur gas, dimethylsulfide, but no studies have been reported on the mechanisms for its microbiological degradation. Three novel strains of bacteria have been isolated from enrichment cultures provided with dimethylsulfone as the only carbon and energy substrate. These are novel facultatively methylotrophic species of Hyphomicrobium and Arthrobacter, capable of growth on a range of one-carbon substrates. Cell-free extracts contained activities of enzymes necessary for a reductive/oxidative pathway for dimethylsulfone degradation: membrane-bound-dimethylsulfone and dimethylsulfoxide reductases, dimethylsulfide monooxygenase, and methanethiol oxidase. Enzymatic evidence is also presented for the subsequent oxidation of formaldehyde by formaldehyde and formate dehydrogenases in the Hyphomicrobium strain and by a dissimilatory ribulose monophosphate cycle in the Arthrobacter strains. The strains also grew on dimethylsulfoxide and dimethylsulfide, and dimethylsulfide-grown bacteria oxidized dimethylsulfide and dimethylsulfoxide but not dimethylsulfone. Formaldehyde assimilation was effected in the Hyphomicrobium strain by the serine pathway, but enzymes of the ribulose monophosphate cycle for formaldehyde assimilation were present in the Arthrobacter strains grown on dimethylsulfone. In contrast, one of the Arthrobacter strains was shown to switch to the serine pathway during growth on methanol. Growth yields on dimethylsulfone and formaldehyde were consistent with the occurrence of the serine pathway in Hyphomicrobium strain S1 and the ribulose monophosphate cycle in Arthrobacter strain TGA, and with the proposed reductive pathway for dimethylsulfone degradation in both.

Keywords: Dimethylsulfone Methylotrophy Dimethylsulfone reductase Serine pathway Hyphomicrobium Arthrobacter

Characterization of the Sinorhizobium meliloti genes encoding a functional dihydrodipicolinate synthase (dapA) and dihydrodipicolinate reductase (dapB) by Fernando M. García-Rodríguez; Sanae Zekri; Nicolás Toro (pp. 438-444).

In bacteria, the known pathways for diaminopimelate (DAP) and lysine biosynthesis share two key enzymes, dihydrodipicolinate synthase and dihydrodipicolinate reductase, encoded by the dapA and dapB genes, respectively. In rhizobia, these genes have not yet been genetically characterized. In this work, by sequence analysis, we identified two divergent open reading frames on the 140-MDa plasmid pRmeGR4b of Sinorhizobium meliloti strain GR4. Termed dapA and dapB, these encode products which show significant sequence similarities to DapA and DapB proteins, respectively. Escherichia coli DAP auxotrophs (dapA and dapB mutants) could be complemented with the pRmeGR4b dapA and dapB genes, indicating that these genes code for functional dihydrodipicolinate synthase and dihydrodipicolinate reductase, respectively. Reverse-transcriptase PCR analyses and β-galactosidase assays using transcriptional dapA-lacZ and dapB-lacZ fusions suggest that these genes are constitutively expressed in S. meliloti. The dapA and dapB genes are not widely distributed in S. meliloti and appear to be specific for strains carrying pRmeGR4b-type plasmids.

Keywords: Diaminopimelate Dihydrodipicolinate synthase Dihydrodipicolinate reductase Lysine

Novel glycoproteins of the halophilic archaeon Haloferax volcanii by Jerry Eichler (pp. 445-448).

Archaea possess many eukaryote-like properties, including the ability to glycosylate proteins. Using oligosaccharide staining and lectin binding, this study revealed the existence of several glycosylated Haloferax volcanii membrane proteins, besides the previously reported surface layer (S-layer) glycoprotein. While the presence of glycoproteins in archaeal S-layers and flagella is well-documented, few archaeal glycoproteins that are not part of these structures have been reported. The glycosylated 150, 98, 58 and 54 kDa protein species detected were neither precursors nor breakdown products of the 190 kDa S-layer glycoprotein. Furthermore, these novel glycoproteins were outwardly oriented and intimately associated with the membrane.

Keywords: Archaea Halophiles Haloferax volcanii Glycoproteins Membranes S-layer

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Archives of Microbiology (v.173, #5-6)