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1.
M. Zahr B. Fobel H. Mayer J. F. Imhoff V. Campos J. Weckesser 《Archives of microbiology》1992,157(6):499-504
Lipopolysaccharides were isolated from the moderate halophilic Ectothiorhodospira shaposhnikovii slight to and Ectothiorhodospira mobilis and from the extremely halophilic Ectothiorhodospira halophila by the hot phenol-water and purified by the phenol-chloroform-petroleum ether methods. The isolated lipopolysaccharides of all three species contained 3-deoxy-d-manno-octulosonic acid and d-glycero-d-mannoheptose indicating the existence of a core. They contained additionally glucose and uronic acids (E. shaposhnikovii and E. mobilis) or glucose, uronic acids and threonine (E. halophila). Sodium deoxycholate gel-electrophoresis of the three lipopolysaccharides, each showing only one major band, indicated R-type character of the lipopolysaccharides of the three Ectothiorhodospira species.The lipid A fractions of the lipopolysaccharides from E. shaposhnikovii and E. mobilis represented phosphorylated mixed lipid A types with both 2,3-diamino-2,3-dideoxy-d-glucose and d-glucosamine. The lipid A from E. halophila contained also phosphate and 2,3-diamino-2,3-dideoxy-d-glucose but only traces of d-glucosamine, which would indicated lipid ADAG. The fatty acid spectra were characterized by amide-bound 3-OH-10:0 and 3-OH-12:0 (E. shaposhnikovii), 3-OH-10:0 (E. mobilis), or 3-OH-10:0,3-OH-14:0, and 3-oxo-14-0 (E. halophila). The predominant ester-bound fatty acids were 14:0 and 16:0 (E. shaposhnikovii and E. mobilis), or 12:0 and 14:1 (E. halophila).Abbreviations DAG
2,3-diamino-2,3-dideoxy-d-glucose
- Kdo
3-deoxy-d-manno-octulosonic acid
- GlcA
glucuronic acid
- GalA
galacturonic acid
- GC-MS
combined gas liquid chromatographymass spectrometry
- GlcN
Glucosamine
- DOC
sodium deoxycholate
- LPS
lipopolysaccharide
- PAGE
polyacrylamide gel electrophoresis
- PCP
phenol-chloroform-petroleum ether 相似文献
2.
The lipopolysaccharide of Ectothiorhodospira vacuolata was obtained by the phenol-water procedure. It contained a 3-O-methyl-hexose, glucose, galacturonic and glucuronic acids. The finding of d-glycero-d-mannoheptose and 2-keto-3-deoxyoctonate (tentatively identified) suggested a core-structure. The lipid fraction of the lipopolysaccharide contained phosphate and both, 2,3-diamino-2,3-dideoxy-d-glucose and d-glucosamine. The major fatty acids were amine-bound 3-OH-10:0 and 3-OH-12:0 and esterbound 14:0 and 16:0 Sodium deoxycholate gel-electrophoresis, showing a single band only, indicated R-type character of the lipopolysaccharide of Ectothiorhodospira vacuolata.Abbreviations DOC
sodium deoxycholate
- GC/MS
combined gasliquid chromatography
- PAGE
polyacrylamide gel-electrophoresis 相似文献
3.
General diffusion pores and specific porin channels from outer membranes of gram-negative bacteria were reconstituted into
lipid bilayer membranes. The current noise of the channels was investigated for the different porins in the open state and
in the ligand-induced closed state using fast Fourier transformation. The open channel noise exhibited 1/f-noise for frequencies up to 200 Hz. The 1/f-noise was investigated using the Hooge formula (Hooge, Phys. Lett.
29A: 139–140 (1969)), and the Hooge parameter α was calculated for all bacterial porins used in this study. The 1/f-noise was in part caused by slow inactivation and activation of porin channels. However, when care was taken that during
the noise measurement no opening or closing of porin channels occurred, the Hooge Parameter α was a meaningful number for a given channel. A linear relationship was observed between α and the single-channel
conductance, g, of the different porins. This linear relation between single-channel conductance and the Hooge parameter α could be qualitatively explained by assuming that the passing of an ion through a bacterial porin channel is—to
a certain extent—influenced by nonlinear effects between channel wall and passing ion.
Received: 8 May 1996/Revised: 27 January 1997 相似文献
4.
M. B. Vainshtein G. I. Gogotova N. -J. Heinritz 《World journal of microbiology & biotechnology》1994,10(1):110-111
When Ectothiorhodospira shaposhnikovii VKM B-1525 was used for desuphurization of biogas in the laboratory and in a pilot plant, there was complete oxidation of H2S, the main product being elemental sulphur. The advatage of this culture over green bacteria is discussed.M.B. Vainshtein, G.I. Gogotova and N.-J. Heinritz are with the Institute of Biochemistry and Physiology of Microorganisms, Russian Academy of Sciences, Pushchino, Moscow Region, 142292 Russia 相似文献
5.
Yeshayahu Nitzan Einat Bokobza Deutsch Izabella Pechatnikov 《Current microbiology》2002,45(6):0446-0455
The penetration of anionic β-lactam antibiotics through porins was evaluated as a mechanism of drug resistance. The major
proteins with porin activity were purified from the outer membranes of six bacteria. Three of the six porins were oligomeric
porins. The molecular weights of their monomers were 37 kDa from Photobacterium damsela, 42 kDa from Serratia liquefaciens, and 36 kDa from E. coli B. The other three porins were heat-modifiable monomeric porins with molecular weights of 43 kDa from Porphyromonas asaccharolytica and Acinetobacter baumannii, and 37 kDa from Escherichia coli K12.
Comparison of the six porin proteins revealed that, independent of their aggregation state, their amino acid content is similar
but not identical. All have double the amount of negatively charged amino acids compared with positively charged amino acids.
They have a similar polarity and polarity index. Two of the six tested bacteria do not produce β-lactamase. These two bacteria
were sensitive to the different β-lactams tested. The other four bacteria were resistant to all or to several β-lactams.
A modified liposome swelling method was used for determining the rate of penetration of charged β-lactam antibiotics. Zwitterionic
β-lactams were found to penetrate into liposomes at a rate that more or less fits their molecular weight, whether the porins
are monomeric or oligomeric. The penetration rates of negatively charged β-lactams are different for oligomeric and monomeric
porins. Negatively charged β-lactams penetrate through oligomeric porins better than estimated by their molecular weight,
whereas monomeric porins are less penetrable to negatively charged β-lactams than estimated by their molecular weight. The
contribution of all types of porins to the susceptibility of bacteria to β-lactam antibiotics (zwitterionic or negatively
charged) is apparently doubtful. The porins may decrease or increase bacterial penetration rates to β-lactams, and only the
existence of a potential β-lactamase that can destroy the penetrating drug will cause resistance.
Received: 28 January 2002 / Accepted: 4 May 2002 相似文献
6.
A major Erwinia amylovora outer-membrane protein (Omp-EA) and the gene encoding for this protein (omp-EA) were isolated and characterized. The native Omp-EA protein forms a trimeric structure of approximately 114 kDa. This protein
demonstrated high resistance to detergents such as SDS and octyl-glucopyranoside, but disaggregated to monomers with a molecular
weight (MW) of approximately 39 kDa after heating at 95°C for 10 minutes in sample buffer. The pore-forming ability of the
oligomeric Omp-EA was determined by the liposome swelling assay, demonstrating that the oligomeric protein formed nonspecific
channels with an exclusion limit of approximately 660 Da. On dissociation, the monomers did not exhibit pore-forming ability.
The omp-EA gene was cloned and sequenced (GenBank Accession No. DQ184680). Sequence analysis revealed an open reading frame of 1152
bases. The deduced amino-acid sequence had 383 amino acids. The mature protein consisted of 362 amino acids and had a calculated
MW of 39,210 Da. Multiple-sequence alignment of Omp-EA with other porins from the Enterobacteriaceae family revealed 51% to 63% identity. The first 16 amino acids from the N-terminal exhibited the highest identity (100%) to
the porins OmpC, OmpF, and PhoE of Escherichia coli. Two methods were used to predict the secondary structure: APSSP2 and Hidden and Markov’s model. The monomers of Omp-EA porin
presented a topology of 16 transmembranal β-strands. The area of the loops between the β -strands was proposed. It is suggested
that further research on the porin and its loops may be important for understanding the mechanism of E. amylovor to invade plant tissues. 相似文献
7.
《Gene》1997,191(2):225-232
The gene coding for the anion-specific porin of the halophilic eubacterium Ectothiorhodospira (Ect.) vacuolata was cloned and sequenced, the first such gene so analyzed from a purple sulfur bacterium. It encodes a precursor protein consisting of 374 amino acid (aa)-residues including a signal peptide of 22-aa residues. Comparison with aa sequences of porins from several other members of the Proteobacteria revealed little homology. Only two regions showed local homology with the previously sequenced porins of Neisseria species, Comamonas acidovorans, Bordetella pertussis, Alcaligenes eutrophus, and Burkholderia cepacia. Genomic Southern blot hybridization studies were carried out with a probe derived from the 5′ end of the gene coding for the porin of Ect. vacuolata. Two related species, Ect. haloalkaliphila and Ect. shaposhnikovii, exhibited a clear signal, while the extremely halophilic bacterium Halorhodospira (Hlr.) halophila (formerly Ect. halophila) did not show any cross-hybridization even at low stringency. This result is in good accordance with a recently proposed reassignment within the family Ectothiorhodospiraceae, which included the separation of the extremely halophilic species into the new genus Halorhodospira. 相似文献
8.
John L. Wylie Christine Bernegger-Egli Joe D. J. O'Neil Elizabeth A. Worobec 《Journal of bioenergetics and biomembranes》1993,25(5):547-556
OprB, a glucose-inducible porin ofP. aeruginosa, was characterized by black lipid bilayer analysis and circular dichroism spectroscopy. Black lipid bilayer analysis of OprB revealed a single-channel conductance of 25 pS, the presence of a glucose binding site with aK
s for glucose of 380 ± 40 mM, and the formation of channels with a strong selection for anions. Analysis ofP. aeruginosa OprB circular dichroism spectra revealed a high sheet content (40%) which is within the range of that determined for other porins. Values obtained from black lipid bilayer analysis were compared to those previously obtained for OprB ofP. putida [Saravolacet al. (1991).J. Bacteriol.
173, 4970–4976] and indicated extensive similarities in the single-channel conductance and glucose-binding properties of these two porins. Immunological and amino terminal sequence analysis revealed a high degree of homology. Of the first 14 amino terminal residues, 12 were identical. A major difference between the two porins was found in their ion selectivity. WhereasP. aeruginosa OprB is anion selective,P. putida OprB and other carbohydrate selective porins are known to be cation selective. 相似文献
9.
Cooperative interaction of the high-potential hemes (Ch) in the cytochrome subunit of the photosynthesizing bacterium Ectothiorhodospira shaposhnikovii was studied by comparing redox titration curves of the hemes under the conditions of pulse photoactivation inducing single
turnover of electron-transport chain and steady-state photoactivation, as well as by analysis of the kinetics of laser-induced
oxidation of cytochromes by reaction center (RC). A mathematical model of the processes of electron transfer in cytochrome-containing
RC was considered. Theoretical analysis revealed that the reduction of one heme Ch facilitated the reduction of the other heme, which was equivalent to a 60 mV positive shift of the midpoint potential. In
addition, reduction of the second heme Ch caused a three-to four-fold acceleration of the electron transfer from the cytochrome subunit to RC.
Published in Russian in Biokhimiya, 2007, Vol. 72, No. 11, pp. 1540–1547. 相似文献
10.
Sequences of the 16S rRNA gene were determined from all type strains of the recognized Ectothiorhodospira species and from a number of additional strains. For the first time, these data resolve the phylogenetic relationships of
the Ectothiorhodospiraceae in detail, confirm the established species, and improve the classification of strains of uncertain
affiliation. Two major groups that are recognized as separate genera were clearly established. The extremely halophilic species
were removed from the genus Ectothiorhodospira and reassigned to the new genus Halorhodospira gen. nov., to recognize that the most halophilic eubacteria are species of this genus. These species are Halorhodospira halophila comb. nov., Halorhodospira halochloris comb. nov., and Halorhodospira abdelmalekii comb. nov. Among the slightly halophilic Ectothiorhodospira species, the classification of strains belonging to Ectothiorhodospira mobilis and Ectothiorhodospira shaposhnikovii was improved. Several strains that were tentatively identified as Ectothiorhodospira mobilis form a separate cluster on the basis of their 16S rDNA sequences and are recognized as two new species: Ectothiorhodospira haloalkaliphila sp. nov., which includes the most alkaliphilic strains originating from strongly alkaline soda lakes, and Ectothiorhodospira marina, describing isolates from the marine environment.
Received: 12 October 1995 / Accepted: 1 December 1995 相似文献
11.
I. A. Bryantseva T. P. Tourova O. L. Kovaleva N. A. Kostrikina V. M. Gorlenko 《Microbiology》2010,79(6):780-790
Two strains of purple sulfur bacteria of the family Ectothiorhodospiraceae were isolated from moderately saline steppe lakes (with pH above 9.0) of the Transbaikal region (strain B7-7) and Mongolia
(strain M10). The cells of the novel strains were spiral-shaped, 2.0–3.2 × 9.6–20.0 μm, motile due to a polar tuft of flagella.
Photosynthetic pigments were represented by bacteriochlorophyll a and carotenoids of the spirilloxanthin series. Photosynthetic membranes were represented by long strands of lamellae distributed
throughout the whole cell; unlike most Ectothiorhodospiraceae species, the membranes were not packed into regular stacks. Bacteria were capable of weak growth on sulfide and slow grow
on hydrogen under photoautotrophic conditions. The best growth was noted on sulfide in the presence of acetate and bicarbonate.
Thiosulfate did not stimulate phototrophic growth, even in the presence of organic substrates. The new isolates were alkaliphiles
growing at a pH optimum of 9–10. Growth was possible within a salinity range of 0–80 g/l NaCl, with an optimum at 5–15 g/l
NaCl. The morphology, the structure of the photosynthetic apparatus (strands of lamellae), and the physiology of the new strains
were similar to those of Thiorhodospira sibirica. However, analysis of the 16S rRNA gene sequences demonstrated that the studied isolates were closely related to the type
strain Ectothiorhodospira shaposhnikovii (99% similarity) of the family Ectothiorhodospiraceae, whereas the level of similarity between the new strains and Thiorhodospira sibirica was only 94–95%. According to the results of DNA-DNA hybridization, the DNA-DNA homology level between the tested strains
was almost 100%; the similarity between the new isolates and the type strain Ectothiorhodospira shaposhnikovii was only 58%. The isolates differed from other representatives of the genus Ectothiorhodospira in the structure of the gene encoding the key enzyme of autotrophic CO2 fixation, ribulose-1,5-bisphosphate carboxylase (RuBisCo), which was similar to the RuBisCo genes of members of another family
of sulfur bacteria, Chromatiaceae. The new isolates of purple bacteria were described as a new species of the genus Ectothiorhodospira, Ect. magna sp. nov. with the type strain B7-7T (= VKM B-2537 = DSM 22250). 相似文献
12.
Johannes F. Imhoff Brian J. Tindall William D. Grant Hans G. Trüper 《Archives of microbiology》1981,130(3):238-242
A new phototrophic bacterium was isolated from Jordanian and Kenyan alkaline salt lakes. Cells are rod shaped, 1.5 m wide and 2–4 m long, and motile by polar flagella. They divide by binary fission, and possess photosynthetic membranes as lamellar stacks similar to those in the other species of the genus Ectothiorhodospira and the brown colored Rhodospirillum species. The presence of bacteriochlorophyll a and carotenoids of the normal spirilloxanthin series is indicated by the absorption spectra of living cells. Under certain growth conditions the cells form gas vacuoles, may become immotile and float to the top of the culture medium. Sulfide and thiosulfate are used as photosynthetic electron donors. During the oxidation of sulfide to sulfate, elemental sulfur is formed, which is accumulated outside the cells. The organisms are strictly anaerobic, do not require vitamins, are moderately halophilic and need alkaline pH-values for growth. The new species Ectothiorhodospira vacuolata is proposed. 相似文献
13.
Avidan O Kaltageser E Pechatnikov I Wexler HM Shainskaya A Nitzan Y 《Archives of microbiology》2008,190(6):641-650
The outer membrane proteins of Desulfovibrio piger and Bilophila wadsworthia (Omp-DP and Omp-BW, respectively) and the genes encoding them (omp-DP and omp-BW) were isolated and characterized. Native Omp-DP and Omp-BW form a trimeric structure of approximately 120 kDa. These proteins
disaggregated into monomers with a molecular weight of approximately 53 kDa after heating at 95°C for 10 min. The pore-forming
abilities of these oligomeric proteins demonstrated that they form small nonspecific channels with an exclusion limit of 260–300 Da.
The omp-DP and omp-BW genes were cloned and sequenced. Sequence analyses revealed an open reading frame of 1,512 bp for omp-DP and 1,440 bp for omp-BW. The mature Omp-DP protein consisted of 480 amino acids and had a calculated MW of 53,290 Da. The mature Omp-BW protein consisted
of 456 amino acids and had a calculated MW of 50.050 Da. Alignment of Omp-DP with Omp-BW revealed 54% homology, whereas alignment
with other known porins showed a low level of homology. Analysis of the secondary structures indicated that both proteins
span the outer membrane 18 times with amphipathic β-strands. This research presents porins which were isolated and characterized
for the first time from bacteria belonging to the Desulfovibrionaceae family.
O. Avidan and E. Kaltageser have contributed equally to this work. 相似文献
14.
Ectothiorhodospira halochloris grows photoheterotrophically with a variety of sulfur sources. During sulfide oxidation to elemental sulfur considerable amounts of polysulfides may be accumulated transiently. When grown on elemental sulfur no sulfate was produced by oxidation, but sulfide and polysulfide were formed by reduction. Only one soluble cytochrome c-551 was isolated and purified. It was a small acidic hemeprotein with a molecular weight of 6,300, an isoelectric point of 3.1 and a redox potential of-11 mV at pH 7.0. It showed three absorption maxima in the reduced state (=551 nm; =523 nm; =417 nm). The addition of various c-type cytochromes to a suspension of spheroplasts stimulated the velocity of sulfide oxidation. This stimulation was best with the small acidic cytochromes from E. halochloris or Ectothiorhodospira abdelmalekii. Sulfide oxidation was stopped by several uncoupling agents, ionophores and electron transport inhibitors. Antimycin A, rotenone and cyanide had no effect on sulfide oxidation.Dedicated to Prof. Dr. H. G. Schlegel on the occasion of his 60th birthday 相似文献
15.
D. K. Chistyulin O. D. Novikova O. Yu. Portnyagina V. A. Khomenko T. I. Vakorina N. Yu. Kim M. P. Isaeva G. N. Likhatskaya T. F. Solov’eva 《Biochemistry (Moscow) Supplemental Series A: Membrane and Cell Biology》2012,6(3):235-242
The polypeptide profile of the porin protein fraction of Yersinia ruckeri, a Gram-negative bacterium causing yersiniosis in fish, has been shown to depend on cultivation temperature. OmpF-like porins are expressed mainly in the outer membrane (OM) of the “cold” variant (4°C) of the microorganism and OmpC-like proteins are expressed in the OM of the “warm” variant (37°C). Both types of porins are present in the OM of Y. ruckeri at room temperature. The OmpF-like porin of the “cold” variant was isolated and characterized. The molecular weight and primary structure of the protein were determined. The methods of optical spectroscopy (circular dichroism and intrinsic protein fluorescence) have shown that the protein has a spatial structure typical of β-structured porins from the OM of Gram-negative bacteria. The functional activity of isolated protein was characterized by the bilayer lipid membrane (BLM) technique. The most probable level of channel conductivity was 320 ± 60 pS, corresponding to the channel conductivity of OmpF porins of the genus Yersinia. The distinctive feature of OmpF porin from Y. ruckeri is high thermostability of its functionally active conformation: the protein forms stable pores in the BLM even after heating to 85°C. 相似文献
16.
Characterisation of channels induced in planar bilayer membranes by detergent solubilised Escherichia coli porins 总被引:2,自引:0,他引:2
Purified OmpF, OmpC, NmpC, PhoE and Lc (Protein 2) porins from the Escherichia coli outer membrane were incorporated into planar phospholipid bilayer membranes and the permeability properties of the pores studied. Triton X-100 solubilised porin samples showed large and reproducible increases in membrane conductivity composed of discreet single-channel events. The magnitude of the cation selectivity found for the porins was in the order OmpC greater than OmpF greater than NmpC = Lc; PhoE was anion selective. For the cation selective porins the cation/anion permeability ratios in a variety of solutes ranged from 6 to 35. Further information on the internal structure of the porins was obtained by examination of the single-channel conductance and this was used to interpret macroscopic observations and to estimate single-channel diameters. The same porins solubilised in SDS exhibited slight conductance increase with no observable single-channel activity. Use of on-line microcomputer techniques confirmed the ohmic current vs. voltage behaviour for all the single porin channels examined. 相似文献
17.
Altered channel properties of porins from Haemophilus influenzae: isolates from cystic fibrosis patients 总被引:3,自引:0,他引:3
Changes in amino-acid sequence of the unique pore-forming protein of H. influenzae (OmpP2; porin) have been associated with increased antimicrobial resistance in H. influenzae strains isolated from cystic fibrosis patients. From patients who were subjected to long-term antimicrobial therapy, H. influenzae strains 67d and 69a (patient 27) and strains 77a and 77f (patient 30) were isolated. Strains 67d and 77a were previously shown to have elevated values for minimal inhibitory concentrations of antibiotics compared to strains 69a and 77f. Porins were extracted from all four H. influenzae strains by detergent treatment and purified to homogeneity by ion exchange chromatography. By reconstitution of the clinical Hi porins into planar lipid bilayers, single-channel conductance, ionic selectivity, and voltage-gating characteristics were assessed. Porins 77a and 77f displayed similar single-channel conductance and ionic selectivity. Current-voltage relationships were determined for the different porins: porin 77f displayed substantial voltage gating at both positive and negative polarity; porin 77a gated at negative polarity only. Porins 67d and 69a showed substantial differences in their pore-forming properties: the single-channel conductance of porin 69a was significantly increased (1.05 nS) relative to porin 67d (0.73 nS). Porin 67d was twice as permeable to cations as porin 69a, and at both positive and negative polarities the extent of voltage gating was greater for porin 67d relative to porin 69a. Expression of the porins in an isogenic, porin-deleted H. influenzae background allowed for assessment of the contribution of each porin to the minimum inhibitory concentrations of various antimicrobial compounds. Porin 67d was found to have a decreased susceptibility to the antimicrobials novobiocin and streptomycin. This decreased susceptibility of porin 67d to novobiocin and streptomycin correlates with its decrease in single-channel conductance. 相似文献
18.
V. M. Gorlenko S. P. Buryukhaev E. B. Matyugina S. V. Borzenko Z. B. Namsaraev I. A. Bryantseva E. N. Boldareva D. Yu. Sorokin B. B. Namsaraev 《Microbiology》2010,79(3):390-401
The physicochemical properties, species composition, and vertical distribution of microorganisms in the water column, shoreline
microbial mat, and small shoreline mud volcanoes of the stratified soda Lake Doroninskoe were investigated in September 2007.
The lake is located in the Transbaikal region, in the permafrost zone (51°25′N; 112°28′E). The maximal depth of the contemporary
lake is about 6 m, the pH value of the water is 9.72, and the water mineralization in the near-bottom horizon is 32.3 g l−1. In summer, the surface oxygen-containing horizon of the water column becomes demineralized to 26.5 g l−1; at a depth of 3.5–4.0 m, an abrupt transition occurs to the aerobic zone containing hydrosulfide (up to 12.56 g l−1). Hydrosulfide was also detected in trace quantities in the upper water horizons. The density stratification of the water
column usually ensures stable anaerobic conditions until the freezing period (November and December). The primary production
of oxygenic phototrophs reached 176–230 μg l−1. High rates of dark CO2 assimilation (61–240 μg l−1) were detected in the chemocline. Within this zone, an alkaliphilic species of sulfur-oxidizing bacteria of the genus Thioalkalivibrio was detected (104 cells ml−1). Lithoheterotrophic bacteria Halomonas spp., as well as bacteriochlorophyll a-containing aerobic anoxygenic phototrophic bacteria (AAP) Roseinatronobacter sp. capable of thiosulfate oxidation, were isolated from samples collected from the aerobic zone (0–3 m). The water transparency
in September was extremely low; therefore, no visible clusters of anoxygenic phototrophic bacteria (APBs) were detected at
the boundary of the hydrosulfide layer. However, purple sulfur bacteria which, according to the results of the 16S rRNA gene
analysis, belong to the species Thioalkalicoccus limnaeus, Ectothiorhodospira variabilis, “Ect. magna,” and Ect. shaposhnikovii, were isolated from samples of deep silt sediments. Ect. variabilis and Ect. shaposhnikovii were the major APB species in the shoreline algo-bacterial mat. The halotolerant bacterium Ect. shaposhnikovii, purple nonsulfur bacteria of the genus Rhodobacter, and AAP of Roseococcus sp. were isolated from the samples collected from mud volcanoes. All these species are alkaliphiles, moderate halophiles,
or halotolerant microorganisms. 相似文献
19.
GABAA receptors composed of α, β and γ subunits display a significantly higher single-channel conductance than receptors comprised
of only α and β subunits. The pore of GABAA receptors is lined by the second transmembrane region from each of its five subunits and includes conserved threonines at
the 6′, 10′ and 13′ positions. At the 2′ position, however, a polar residue is present in the γ subunit but not the α or β
subunits. As residues at the 2′, 6′ and 10′ positions are exposed in the open channel and as such polar channel-lining residues
may interact with permeant ions by substituting for water interactions, we compared both the single-channel conductance and
the kinetic properties of wild-type α1β1 and α1β1γ2S receptors with two mutant receptors, αβγ(S2′A) and αβγ(S2′V). We found
that the single-channel conductance of both mutant αβγ receptors was significantly decreased with respect to wild-type αβγ,
with the presence of the larger valine side chain having the greatest effect. However, the conductance of the mutant αβγ receptors
remained larger than wild-type αβ channels. This reduction in the conductance of mutant αβγ receptors was observed at depolarized
potentials only (ECl = −1.8 mV), which revealed an asymmetry in the ion conduction pathway mediated by the γ2′ residue. The substitutions at the
γ2′ serine residue also altered the gating properties of the channel in addition to the effects on the conductance with the
open probability of the mutant channels being decreased while the mean open time increased. The data presented in this study
show that residues at the 2′ position in M2 of the γ subunit affects both single-channel conductance and receptor kinetics. 相似文献
20.
Serratia marcescens outer membrane contains three different general diffusion porins: Omp1, Omp2 and Omp3. Omp1 was cloned and sequenced and it shows a great homology to the family of outer membrane porins that comprises the general porins of enteric bacteria. The gene for Omp1 was transferred into an expression plasmid and was expressed in Escherichia coli UH302 (E. coli UH302 pOM100), a porin deficient strain. Its expression confers a higher susceptibility towards different antibiotics to this strain. Omp1 was purified to homogeneity from outer membrane of E. coli UH302 pOM100. Reconstitution of the purified protein into black lipid bilayers demonstrated that it is a channel-forming component with a single-channel conductance of approximately 2 nS in 1 M KCl similar to that of other porins from enteric bacteria. Omp1 is slightly cation-selective. Its homology to already crystallised members of the family of enteric porins whose three-dimensional-structures are known and allowed the design of a topology model for Omp1. The charge distribution within a porin monomer is similar as in other general diffusion pores. The positively charged amino acids localised at the beta-strands opposite the external loop L3, which restrict the pore diameter in the porin monomer. 相似文献