The nomenclatural type of the genus Deleya and the consequences of Deleya aesta and Alcaligenes aquamarinus being synonyms. (1/47)

The genus Deleya was created to encompass a number of marine organisms that had previously been classified in diverse genera. Deleya aesta was designated as the type species of the genus. Subsequent work indicated that Deleya aesta, Alcaligenes aquamarinus and Alcaligenes faecalis subsp. homari were heterotypic synonyms. Consequently, Akagawa & Yamasato (Int J Syst Bacteriol 39, 462-466, 1989) concluded that, based on Rules 23a and 51b of the Bacteriological Code (1975 Revision), the oldest legitimate species epithet was aquamarinus and the type species of the genus Deleya should therefore be changed to Deleya aquamarina. Dobson & Franzmann (Int J Syst Bacteriol 46, 550-558, 1996) concluded that it was not possible to distinguish between members of the genus Deleya and members of the genus Halomonas Vreeland et al. 1980, leading them to transfer members of the genus Deleya to the genus Halomonas and resulting in the creation of a new combination, Halomonas aquamarina. Closer examination of some of these changes indicates that they are not all in accordance with the Rules of the Bacteriological Code (1975 or 1990 Revisions).  (+info)

Highly efficient renaturation of beta-lactamase isolated from moderately halophilic bacteria. (2/47)

Most, if not all, beta-lactamases reported to date are irreversibly denatured at 60-70 degrees C. Here, we found that a halophilic beta-lactamase from the moderately halophilic bacterium Chromohalobacter sp. 560 was highly stable against heat inactivation: it retained approximately 75% of its activity after boiling for 5 min in the presence of 0.2 M NaCl, suggesting that the protein either incompletely denatures during the boiling process or readily renatures upon cooling to the assay temperature. Circular dichroism showed a complete unfolding at 60 degrees C and a full reversibility, indicating that the observed activity after boiling is due to efficient refolding following heat denaturation. The enzyme showed optimal activity at 50-60 degrees C, indicating that an increase in activity with temperature offsets the thermal denaturation. The gene bla was cloned, and the primary structure of the enzyme was deduced to be highly abundant in acidic amino acid residues, one of the characteristics of halophilic proteins. Despite its halophilic nature, the enzyme refolds in low salt media after heat denaturation.  (+info)

Salt-inducible multidrug efflux pump protein in the moderately halophilic bacterium Chromohalobacter sp. (3/47)

It has been known that halophilic bacteria often show natural resistance to antibiotics, dyes, and toxic metal ions, but the mechanism and regulation of this resistance have remained unexplained. We have addressed this question by identifying the gene responsible for multidrug resistance. A spontaneous ofloxacin-resistant mutant derived from the moderately halophilic bacterium Chromohalobacter sp. strain 160 showed a two- to fourfold increased resistance to structurally diverse compounds, such as tetracycline, cefsulodin, chloramphenicol, and ethidium bromide (EtBr), and tolerance to organic solvents, e.g., hexane and heptane. The mutant produced an elevated level of the 58-kDa outer membrane protein. This mutant (160R) accumulated about one-third the level of EtBr that the parent cells did. An uncoupler, carbonyl cyanide m-chlorophenylhydrazone, caused a severalfold increase in the intracellular accumulation of EtBr, with the wild-type and mutant cells accumulating nearly equal amounts. The hrdC gene encoding the 58-kDa outer membrane protein has been cloned. Disruption of this gene rendered the cells hypersusceptible to antibiotics and EtBr and led to a high level of accumulation of intracellular EtBr. The primary structure of HrdC has a weak similarity to that of Escherichia coli TolC. Interestingly, both drug resistance and the expression of HrdC were markedly increased in the presence of a high salt concentration in the growth medium, but this was not observed in hrdC-disrupted cells. These results indicate that HrdC is the outer membrane component of the putative efflux pump assembly and that it plays a major role in the observed induction of drug resistance by salt in this bacterium.  (+info)

Complex regulation of the synthesis of the compatible solute ectoine in the halophilic bacterium Chromohalobacter salexigens DSM 3043T. (4/47)

The synthesis of the compatible solute ectoine, mediated by the ectABC gene products, is the main mechanism used by the halophilic bacterium Chromohalobacter salexigens to cope with osmotic stress. Evidence was found that this process is regulated at the transcriptional level. S1 protection analyses performed with RNA extracted from cells grown in minimal medium at low (0.75 M NaCl) or high (2.5 M NaCl) osmolarity suggested the existence of four promoters upstream of ectA. Two of these (PectA1 and PectA2) might be recognized by the main vegetative sigma factor sigma(70), and one (PectA3) might be dependent on the general stress sigma factor sigma(S). The S1 protection assays suggest that PectA1 and PectA3 may be osmoregulated promoters. In addition, an internal promoter showing sequences homologous to promoters dependent on the heat-shock sigma factor sigma(32) was found upstream of ectB. Transcription from PectA in C. salexigens followed a pattern typical of sigma(S)-dependent promoters, and was reduced by 50 % in an E. coli rpoS background. These data strongly suggest the involvement of the general stress sigma factor sigma(S) in ectABC transcription in C. salexigens. Expression of PectA-lacZ and PectB-lacZ trancriptional fusions was very high at low salinity, suggesting that ectABC may be a partially constitutive system. Both transcriptional fusions were induced during continuous growth at high temperature and their expression was reduced in cells grown in the presence of osmoprotectants (ectoine or glycine betaine) or the DNA gyrase inhibitor nalidixic acid. Moreover, PectA-lacZ expression was negatively modulated in cells grown with an excess of iron (FeCl(3)). Measurement of ectoine levels in the presence of glycine betaine at different NaCl concentrations suggests that an additional post-transcriptional control may occur as well.  (+info)

Chromohalobacter sarecensis sp. nov., a psychrotolerant moderate halophile isolated from the saline Andean region of Bolivia. (5/47)

A moderately halophilic, aerobic, motile, Gram-negative, rod-shaped bacterium (strain LV4(T)) was isolated from saline soil around the lake Laguna Verde in the Bolivian Andes. The organism is a heterotroph, able to utilize various carbohydrates as a carbon source. It showed tryptophan deaminase, oxidase and catalase activity, but was unable to produce indole or H(2)S; nitrate was not reduced. The G+C content of the genomic DNA was 56.1 mol%. The pH range for growth was 5-10, temperature range was 0-45 degrees C and the range of NaCl concentrations was 0-25 % (w/v). On the basis of 16S rRNA gene sequence analysis, strain LV4(T) was found to be closely related to Chromohalobacter canadensis DSM 6769(T) and Pseudomonas beijerinckii DSM 7218(T); however, its DNA-DNA relatedness with these type strains was low. Strain LV4(T) resembled other Chromohalobacter species with respect to various physiological, biochemical and nutritional characteristics but also exhibited differences. Thus, a novel species, Chromohalobacter sarecensis sp. nov., is proposed, with LV4(T) (=CCUG 47987(T)=ATCC BAA-761(T)) as the type strain.  (+info)

Identification of an amino acid position that determines the substrate range of integral membrane alkane hydroxylases. (6/47)

Selection experiments and protein engineering were used to identify an amino acid position in integral membrane alkane hydroxylases (AHs) that determines whether long-chain-length alkanes can be hydroxylated by these enzymes. First, substrate range mutants of the Pseudomonas putida GPo1 and Alcanivorax borkumensis AP1 medium-chain-length AHs were obtained by selection experiments with a specially constructed host. In all mutants able to oxidize alkanes longer than C13, W55 (in the case of P. putida AlkB) or W58 (in the case of A. borkumensis AlkB1) had changed to a much less bulky amino acid, usually serine or cysteine. The corresponding position in AHs from other bacteria that oxidize alkanes longer than C13 is occupied by a less bulky hydrophobic residue (A, V, L, or I). Site-directed mutagenesis of this position in the Mycobacterium tuberculosis H37Rv AH, which oxidizes C10 to C16 alkanes, to introduce more bulky amino acids changed the substrate range in the opposite direction; L69F and L69W mutants oxidized only C10 and C11 alkanes. Subsequent selection for growth on longer alkanes restored the leucine codon. A structure model of AHs based on these results is discussed.  (+info)

Mercury adaptation among bacteria from a deep-sea hydrothermal vent. (7/47)

Since deep-sea hydrothermal vent fluids are enriched with toxic metals, it was hypothesized that (i) the biota in the vicinity of a vent is adapted to life in the presence of toxic metals and (ii) metal toxicity is modulated by the steep physical-chemical gradients that occur when anoxic, hot fluids are mixed with cold oxygenated seawater. We collected bacterial biomass at different distances from a diffuse flow vent at 9 degrees N on the East Pacific Rise and tested these hypotheses by examining the effect of mercuric mercury [Hg(II)] on vent bacteria. Four of six moderate thermophiles, most of which were vent isolates belonging to the genus Alcanivorax, and six of eight mesophiles from the vent plume were resistant to >10 microM Hg(II) and reduced it to elemental mercury [Hg(0)]. However, four psychrophiles that were isolated from a nearby inactive sulfide structure were Hg(II) sensitive. A neighbor-joining tree constructed from the deduced amino acids of a PCR-amplified fragment of merA, the gene encoding the mercuric reductase (MR), showed that sequences obtained from the vent moderate thermophiles formed a unique cluster (bootstrap value, 100) in the MR phylogenetic tree, which expanded the known diversity of this locus. The temperature optimum for Hg(II) reduction by resting cells and MR activity in crude cell extracts of a vent moderate thermophile corresponded to its optimal growth temperature, 45 degrees C. However, the optimal temperature for activity of the MR encoded by transposon Tn501 was found to be 55 to 65 degrees C, suggesting that, in spite of its original isolation from a mesophile, this MR is a thermophilic enzyme that may represent a relic of early evolution in high-temperature environments. Results showing that there is enrichment of Hg(II) resistance among vent bacteria suggest that these bacteria have an ecological role in mercury detoxification in the vent environment and, together with the thermophilicity of MR, point to geothermal environments as a likely niche for the evolution of bacterial mercury resistance.  (+info)

Alcanivorax dieselolei sp. nov., a novel alkane-degrading bacterium isolated from sea water and deep-sea sediment. (8/47)

Two bacterial strains, B-5(T) and NO1A, were isolated from the surface water of the Bohai Sea and deep-sea sediment of the east Pacific Ocean, respectively. Both strains were halophilic, aerobic, Gram-negative, non-spore-forming, catalase- and oxidase-positive motile rods. They grew on a restricted spectrum of organic compounds, including some organic acids and alkanes. On the basis of 16S rRNA gene sequence similarity, strains B-5(T) and NO1A were shown to belong to the gamma-Proteobacteria. Highest similarity values were found with Alcanivorax venustensis (95.2 %), Alcanivorax jadensis (94.6 %) and Alcanivorax borkumensis (94.1 %). Principal fatty acids of both strains were C(16 : 0), C(16 : 1)omega7c and C(18 : 1)omega7c. The chemotaxonomically characteristic fatty acid C(19 : 0) cyclo omega8c was also detected. On the basis of the above, together with results of physiological and biochemical tests, DNA-DNA hybridization, comparisons of 16S-23S internal transcribed spacer sequences and comparisons of the partial deduced amino acid sequence of alkane hydroxylase, both strains were affiliated to the genus Alcanivorax but were differentiated from recognized Alcanivorax species. Therefore, a novel species, Alcanivorax dieselolei sp. nov., represented by strains B-5(T) and NO1A is proposed, with the type strain B-5(T) (=DSM 16502(T)=CGMCC 1.3690(T)).  (+info)

• 1
• 2
• 3
• 4
• 5
• 6