Biomedical subjects

Montserrat Argandoña

Publications and source records attributed to Montserrat Argandoña.

6 recordsLinked to original sources

PubMed2006

A membrane-bound nitrate reductase encoded by the narGHJI operon is responsible for anaerobic respiration in Halomonas maura.

The halophilic bacterium Halomonas maura is capable of anaerobic respiration on nitrates. By insertional mutagenesis with the minitransposon Tn-5 we obtained the mutant Tc62, which was incapable of anaerobic respiration on nitrates. An analysis of the regions adjacent to the transposon allowed us to characterize the membrane-bound anaerobic-respiratory nitrate reductase narGHJI gene cluster in H. maura. We identified consensus sequences for fumarate and nitrate reductase regulator (FNR)-like protein-binding sites in the promoter regions of the nar genes and consensus sequences corresponding to the NarL binding sites upstream of the nar genes. RT-PCR analysis showed that the narGHJI operon was expressed in response to anaerobic conditions when nitrate was available as electron acceptor. This membrane-bound nitrate reductase is the only enzyme responsible for anaerobic respiration on nitrate in H. maura. In this article we discuss the possible relationship between this enzyme and a dissimilatory nitrate-reduction-to-ammonia process (DNRA) in H. maura and its role in the colonization of the rhizosphere.

Anaerobiosis↗

PubMed2006

The ectD gene, which is involved in the synthesis of the compatible solute hydroxyectoine, is essential for thermoprotection of the halophilic bacterium Chromohalobacter salexigens.

The halophilic bacterium Chromohalobacter salexigens synthesizes and accumulates compatible solutes in response to salt and temperature stress. (13)C-nuclear magnetic resonance analysis of cells grown in minimal medium at the limiting temperature of 45 degrees C revealed the presence of hydroxyectoine, ectoine, glutamate, trehalose (not present in cells grown at 37 degrees C), and the ectoine precursor, Ngamma-acetyldiaminobutyric acid. High-performance liquid chromatography analyses showed that the levels of ectoine and hydroxyectoine were maximal during the stationary phase of growth. Accumulation of hydroxyectoine was up-regulated by salinity and temperature, whereas accumulation of ectoine was up-regulated by salinity and down-regulated by temperature. The ectD gene, which is involved in the conversion of ectoine to hydroxyectoine, was isolated as part of a DNA region that also contains a gene whose product belongs to the AraC-XylS family of transcriptional activators. Orthologs of ectD were found within the sequenced genomes of members of the proteobacteria, firmicutes, and actinobacteria, and their products were grouped into the ectoine hydroxylase subfamily, which was shown to belong to the superfamily of Fe(II)- and 2-oxoglutarate-dependent oxygenases. Analysis of the ectoine and hydroxyectoine contents of an ectABC ectD mutant strain fed with 1 mM ectoine or hydroxyectoine demonstrated that ectD is required for the main ectoine hydroxylase activity in C. salexigens. Although in minimal medium at 37 degrees C the wild-type strain grew with 0.5 to 3.0 M NaCl, with optimal growth at 1.5 M NaCl, at 45 degrees C it could not cope with the lowest (0.75 M NaCl) or the highest (3.0 M NaCl) salinity, and it grew optimally at 2.5 M NaCl. The ectD mutation caused a growth defect at 45 degrees C in minimal medium with 1.5 to 2.5 M NaCl, but it did not affect growth at 37 degrees C at any salinity tested. With 2.5 M NaCl, the ectD mutant synthesized 38% (at 37 degrees C) and 15% (at 45 degrees C) of the hydroxyectoine produced by the wild-type strain. All of these data reveal that hydroxyectoine synthesis mediated by the ectD gene is thermoregulated and essential for thermoprotection of C. salexigens.

Adaptation, Physiological↗

PubMed2005

The moderately halophilic bacterium Halomonas maura is a free-living diazotroph.

Halomonas maura is a moderately halophilic bacterium which lives in saline soils and synthesises an exopolysaccharide known as mauran. Strain S-31T grew in a nitrogen-free medium under an N2 atmosphere; the acetylene reduction assay proved positive under specific conditions. We identified the nifH gene in this strain by using degenerate oligonucleotides designed from highly preserved gene sequences obtained from the alignment of a large number of nifH sequences from different microorganisms. Our results lead us to conclude that H. maura is capable of fixing nitrogen under microaerobic conditions.

Base Sequence↗

PubMed2005

epsABCJ genes are involved in the biosynthesis of the exopolysaccharide mauran produced by Halomonas maura.

The moderately halophilic strain Halomonas maura S-30 produces a high-molecular-mass acidic polymer (4.7 x 10(6) Da) composed of repeating units of mannose, galactose, glucose and glucuronic acid. This exopolysaccharide (EPS), known as mauran, has interesting functional properties that make it suitable for use in many industrial fields. Analysis of the flanking regions of a mini-Tn5 insertion site in an EPS-deficient mutant of H. maura, strain TK71, led to the identification of five ORFs (epsABCDJ), which form part of a gene cluster (eps) with the same structural organization as others involved in the biosynthesis of group 1 capsules and some EPSs. Conserved genetic features were found such as JUMPstart and ops elements, which are characteristically located preceding the gene clusters for bacterial polysaccharides. On the basis of their amino-acid-sequence homologies, their putative hydropathy profiles and the effect of their mutations, it is predicted that EpsA (an exporter-protein homologue belonging to the OMA family) and EpsC (a chain-length-regulator homologue belonging to the PCP family) play a role in the assembly, polymerization and translocation of mauran. The possibility that mauran might be synthesized via a Wzy-like biosynthesis system, just as it is for many other polysaccharides, is also discussed. This hypothesis is supported by the fact that EpsJ is homologous with some members of the PST-exporter-protein family, which seems to function together with each OMA-PCP pair in polysaccharide transport in Gram-negative bacteria, transferring the assembled lipid-linked repeating units from the cytoplasmic membrane to the periplasmic space. Maximum induction of the eps genes is reached during stationary phase in the presence of 5 % (w/v) marine salts.

Amino Acid Sequence↗

PubMed2003

Megaplasmids in Gram-negative, moderately halophilic bacteria.

We have discovered that many Halomonas species harbour large extrachromosomal DNA elements. Using currently available protocols it is technically very difficult to identify large plasmids in bacteria, and even more so when they are coated in mucous polysaccharide. We used culture conditions suitable for both halophilic and halophilic exopolysaccharide-producing bacteria and applied a modified gel electrophoresis method to locate and visualise the megaplasmids. Almost all the species of Halomonas studied harbour two plasmids of about 70 kb and 600 kb and some species carry other smaller extrachromosomal DNA elements. The common presence of these megaplasmids may well be related to the survival strategies of the bacteria in their special surroundings.

DNA, Bacterial↗

PubMed2002

Analysis of the genome of the moderate halophile Halomonas eurihalina.

We have studied the genomic organization of Halomonas eurihalina, a moderately halophilic bacterium that produces an anionic exopolysaccharide with a potentially wide range of applications in industry. To estimate the genome size of strain F2-7, large restriction fragments of genomic DNA were separated by pulsed-field gel electrophoresis. According to the average size of the resolved restriction fragments, the genome size of H. eurihalina strain F2-7 was estimated to be around 2500 kb. The physical map of the chromosome for the endonuclease SwaI has been constructed. The F2-7 strain has two plasmids, pVE1 and pVE2, and in this study we have isolated three new plasmids, pVE3, pVE4, and pVE5, of 5.3, 16, and 6.5 kb, respectively, from strains H-1, H-217, and H-236 of H. eurihalina. We have characterized these plasmids and constructed their physical maps. Curing experiments produced no evidence for the involvement of these plasmids in the expression of the mucous phenotype.

Blotting, Southern↗