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At least 127 records · Page 7Linked to original sources
PubMed2003

Isolation and characterization of an indigenous isolate of Dunaliella sp. for beta-carotene and glycerol production from a hypersaline lake in India.

Dunaliella, a green alga grows in a wide range of marine and freshwater habitats such as oceans, brine lakes, salt marshes and salt-water ditches near the sea, predominantly in water bodies containing more than 10% salt. Sambhar salt lake, Rajasthan (India) was found as one of the natural habitat of Dunaliella sp. The species was isolated and screened for accumulation of beta-carotene and glycerol. It was studied for the growth attributes like total protein, optical density, total chlorophyll, total carotenoid, beta-carotene and glycerol. Under unstressed physico-chemical conditions the maximum beta-carotene and glycerol observed was 1.15 pg/cell and 94.26 pg/cell respectively. The stress (salt stress (NaCl), high light intensities and continuous light) allowed the alga to accumulate high beta-carotene (approximately 4.21 pg/cell under 118.18 micromole m(-2) s(-1) of light intensity) without massive reduction in biomass content. This opens up new avenues for exploring this strain for future research and its commercial exploitation.

Algal Proteins↗
PubMed2003

Phylogenetic and physiological characterization of a filamentous anoxygenic photoautotrophic bacterium ' Candidatus Chlorothrix halophila' gen. nov., sp. nov., recovered from hypersaline microbial mats.

We report the phylogenetic and physiological characterization of a mesophilic and halophilic member of the filamentous anoxygenic phototrophic (FAP) bacteria, provisionally named ' Candidatus Chorothrix halophila' gen. nov. sp. nov., that has been maintained in a highly enriched culture in our laboratory for over a decade. Phylogenetic analysis of small-subunit RNA-encoding sequences places ' Candidatus Chlorothrix halophila' in a clade that includes cultivated members of the genera Chloroflexus and Oscillochloris. Physiological studies demonstrated sulfide-dependent photosynthetic uptake of (14)C-labeled bicarbonate. Enzymatic assays for the activity of propionyl-coenzyme A synthase indicated that ' Candidatus Chlorothrix halophila' does not use the 3-hydroxypropionate cycle of Chloroflexus aurantiacus OK-70-fl for autotrophic carbon assimilation. New concepts regarding the taxonomy and phylogeny of FAP bacteria have emerged from this work.

Bacterial Physiological Phenomena↗
PubMed2003

Survival of filamentous fungi in hypersaline Dead Sea water.

A variety of filamentous fungi have recently been isolated from the Dead Sea (340 g/L total dissolved salts). To assess the extent to which such fungi can survive for prolonged periods in Dead Sea water, we examined the survival of both spores and mycelia in undiluted Dead Sea water and in Dead Sea water diluted to different degrees with distilled water. Mycelia of Aspergillus versicolor and Chaetomium globosum strains isolated from the Dead Sea remained viable for up to 8 weeks in undiluted Dead Sea water. Four Dead Sea isolates (A. versicolor, Eurotium herbariorum, Gymnascella marismortui, and C. globosum) retained their viability in Dead Sea water diluted to 80% during the 12 weeks of the experiment. Mycelia of all species survived for the full term of the experiment in Dead Sea water diluted to 50% and 10% of its original salinity. Comparison of the survival of Dead Sea species and closely related isolates obtained from other locations showed prolonged viability of the strains obtained from the Dead Sea. Spores of isolates obtained from the terrestrial shore of the Dead Sea generally proved less tolerant to suspension in undiluted Dead Sea water than spores of species isolated from the water column. Spores of the species isolated from the control sites had lost their viability in undiluted Dead Sea water within 12 weeks. However, with the exception of Emericella spores, which showed poor survival, a substantial fraction of the spores of Dead Sea fungal isolates remained viable for that period. The difference in survival rate between spores and mycelia of isolates of the same species points to the existence of adapted halotolerant and/or halophilic fungi in the Dead Sea.

Fungi↗
PubMed2004

Biogeochemistry of an iron-rich hypersaline microbial mat (Camargue, France).

In situ microsensor measurements were combined with biogeochemical methods to determine oxygen, sulfur, and carbon cycling in microbial mats growing in a solar saltern (Salin-de-Giraud, France). Sulfate reduction rates closely followed the daily temperature changes and were highest during the day at 25 degrees C and lowest during the night at 11 degrees C, most probably fueled by direct substrate interactions between cyanobacteria and sulfate-reducing bacteria. Sulfate reduction was the major mineralization process during the night and the contribution of aerobic respiration to nighttime DIC production decreased. This decrease of aerobic respiration led to an increasing contribution of sulfide (and iron) oxidation to nighttime O2 consumption. A peak of elemental sulfur in a layer of high sulfate reduction at low sulfide concentration underneath the oxic zone indicated anoxygenic photosynthesis and/or sulfide oxidation by iron, which strongly contributed to sulfide consumption. We found a significant internal carbon cycling in the mat, and sulfate reduction directly supplied DIC for photosynthesis. The mats were characterized by a high iron content of 56 micromol Fe cm(-3), and iron cycling strongly controlled the sulfur cycle in the mat. This included sulfide precipitation resulting in high FeS contents with depth, and reactions of iron oxides with sulfide, especially after sunset, leading to a pronounced gap between oxygen and sulfide gradients and an unusual persistence of a pH peak in the uppermost mat layer until midnight.

Biochemical Phenomena↗
PubMed2003

Characterization of microbial diversity in hypersaline environments by melting profiles and reassociation kinetics in combination with terminal restriction fragment length polymorphism (T-RFLP).

The diversity of prokaryotes inhabiting solar saltern ponds was determined by thermal melting and reassociation of community DNA. These measurements were compared with fingerprinting techniques such as terminal restriction fragment length polymorphisms (T-RFLP) analysis, denaturant gradient gel electrophoresis (DGGE), and cloning and sequencing approaches. Three ponds with salinities of 22, 32, and 37% (NaCl saturation) were studied. The combination of independent molecular techniques to estimate the total genetic diversity provided a realistic assessment to reveal the microbial diversity in these environments. The changes in the prokaryotic communities at different salinity (22, 32, and 37% salt) were significant and revealed that the total genetic diversity increased from 22% to 32% salinity. At 37% salinity the diversity was reduced again to nearly half that at 22% salinity. Our results revealed that the community "genome" had a DNA complexity that was 7 (in 22% salinity pond), 13 (in 32% salinity pond), and 4 (in 37% salinity pond) times the complexity of an Escherichia coli genome. The base composition profiles showed two abundant populations, which changed in relative amount between the three ponds. They indicated an uneven taxon distribution at 22% and 37% salinity and a more even distribution at 32% salinity. The results indicated a large predominating population at 37% salinity, which might correspond to the abundance of square archaea (SPhT) observed by transmission electron microscopy (TEM) and also indicated by the same T-RFLP fragment as the SPhT. The SPhT phylotype has also been reported to be the most frequently retrieved phylotype from this environment by culture independent techniques. In addition, two different operational taxonomic units (OTU) were detected at 37% salinity based on PCR with bacterial specific primers and T-RFLP. One of these predominant phylotypes is the extreme halophilic bacterium belonging to the bacteroidetes group, Salinibacter ruber.

Bacteria↗
PubMed1998

Moderately halophilic gram-positive bacterial diversity in hypersaline environments.

Moderately halophilic bacteria are microorganisms that grow optimally in media containing 3%-15% (w/v) salt. They are represented by a heterogeneous group of microorganisms included in many different genera. Gram-negative moderately halophilic bacteria have been studied in more detail, but studies on gram-positive species are more scarce. Recent studies carried out by our research group on gram-positive moderate halophiles have permitted clarifying their taxonomic and phylogenetic position and describing new species. Thus, we have isolated six strains from ponds of salterns that show phenotypic and genotypic characteristics similar to those of Nesterenkonia halobia (formerly Micrococcus halobius), a moderately halophilic gram-positive coccus that was described on the basis of a single strain. Our data demonstrate quite clearly that they are members of this species and contribute to a better description of these moderately halophilic cocci. Similarly, a study of a large number of gram-positive moderately halophilic rods that were able to produce endospores led us to describe a new species, designated Bacillus salexigens. Further, isolates grouped in other three phenons, obtained by numerical taxonomy analysis and showing phenotypic features quite similar to those of this species, represent different genomovars, with very low DNA-DNA homology. Although they might represent additional new species, it will be necessary to determine new phenotypic features to differentiate them from previously described Bacillus species. We have also studied the viability of some old enrichments provided by B.E. Volcani, which were set up in 1936. We isolated 31 gram-positive motile endospore-forming rods that, according to their phenotypic characteristics, could represent a new species of the genus Bacillus.

Bacillus↗
PubMed2006

Effect of hypo- and hypersaline conditions on osmolality and Na+/K+-ATPase activity in juvenile shrimp (Litopenaeus vannamei) fed low- and high-HUFA diets.

Fatty acid composition of cellular membranes can modify permeability and can modulate the activity of Na(+)/K(+)-ATPase. Although highly unsaturated fatty acids (HUFA) improve survival and osmoregulatory capacity to low salinities in penaeid shrimp, the possible mechanisms have not been established. For this purpose the influence of HUFA supplementation in diet (2.9 vs. 34% HUFA proportion to total fatty acids) on osmoregulatory responses of juvenile Litopenaeus vannamei submitted to an acute (15 h) or chronic exposure (21 days), to low (5 g L(-1)) and high salinities (50 g L(-1)) was analyzed. Shrimp fed the high-HUFA diet, had higher concentration of main HUFA (20:5n-3 and 22:6n-3) in polar lipids of gills. Osmotic pressure in hemolymph was significantly affected by salinity in acute (640, 751, 847 mOsm/kg for 5, 30 and 50 g L(-1), respectively), and chronic exposure (645, 713, 814 mOsm/kg), but variations between them were small compared to environmental salinity (206, 832, 1547 mOsm/kg), indicating that osmoregulation was achieved in a matter of hours. An increase in Na(+)/K(+)-ATPase activity was observed only after a chronic exposure to low salinity. Free amino acids (FAA), mainly alanine and arginine, were higher at 30 (control) and 50 g L(-1) in accordance to their role as organic osmolites. Neither osmotic pressure, Na(+)/K(+)-ATPase activity, nor FAA was affected by HUFA supplementation. However, higher water content in gills of shrimp exposed to low salinities was counteracted by increased HUFA content, which could be a result of changes in water permeability of gills. The osmoregulatory capacity of penaeid shrimp to low and high salinities was achieved within 15 h of acclimation and did not depend on HUFA supplementation in the diet.

Amino Acids↗
PubMed2004

The effect of temperature on juvenile Mozambique tilapia hybrids (Oreochromis mossambicus x O. urolepis hornorum) exposed to full-strength and hypersaline seawater.

The effects of temperature on the salinity tolerance of Mozambique-Wami tilapia hybrids (Oreochromis mossambicus x O. urolepis hornorum) were investigated by transferring 35 g/l, 25 degrees C-acclimated fish to 35, 43, 51 or 60 g/l salinity at 15, 25 or 35 degrees C for 24 h, and by assaying gill tissue for branchial Na(+), K(+)-ATPase activity at the three temperatures after acclimating the fish to 15, 25 or 35 degrees C for 2 weeks. Tilapia survived all salinities at 25 and 35 degrees C; however, at 15 degrees C, mortality was 85.7% and 100% in the 51 g/l and 60 g/l groups, respectively. There was a significant interaction between temperature and salinity, as plasma osmolality, [Na(+)] and [Cl(-)] were significantly increased at 51 and 60 g/l salinity in 35 degrees C water (P<0.001). Additionally, muscle water content was significantly reduced at 43 g/l, 15 degrees C relative to pre-transfer values (P<0.001). Branchial Na(+), K(+)-ATPase activity was reduced at 15 degrees C regardless of acclimation temperature, and 25 degrees C-acclimated gill tissue did not show an increase in activity when assayed at 35 degrees C. Results indicate that the effects of a combined temperature-salinity transfer on plasma osmolality and ion concentrations, as well as muscle water content, are greater than when either challenge is given alone. Additionally, branchial Na(+), K(+)-ATPase activity is altered when assayed at varying temperatures; in the case of 15 degrees C, regardless of acclimation temperature. Our enzyme activity data may indicate the presence of a high temperature isoform of branchial Na(+), K(+)-ATPase enzyme.

Acclimatization↗
PubMed2004

Characterization of functional bacterial groups in a hypersaline microbial mat community (Salins-de-Giraud, Camargue, France).

A photosynthetic microbial mat was investigated in a large pond of a Mediterranean saltern (Salins-de-Giraud, Camargue, France) having water salinity from 70 per thousand to 150 per thousand (w/v). Analysis of characteristic biomarkers (e.g., major microbial fatty acids, hydrocarbons, alcohols and alkenones) revealed that cyanobacteria were the major component of the pond, in addition to diatoms and other algae. Functional bacterial groups involved in the sulfur cycle could be correlated to these biomarkers, i.e. sulfate-reducing, sulfur-oxidizing and anoxygenic phototrophic bacteria. In the first 0.5 mm of the mat, a high rate of photosynthesis showed the activity of oxygenic phototrophs in the surface layer. Ten different cyanobacterial populations were detected with confocal laser scanning microscopy: six filamentous species, with Microcoleus chthonoplastes and Halomicronema excentricum as dominant (73% of total counts); and four unicellular types affiliated to Microcystis, Chroococcus, Gloeocapsa, and Synechocystis (27% of total counts). Denaturing gradient gel electrophoresis of PCR-amplified 16S rRNA gene fragments confirmed the presence of Microcoleus, Oscillatoria, and Leptolyngbya strains (Halomicronema was not detected here) and revealed additional presence of Phormidium, Pleurocapsa and Calotrix types. Spectral scalar irradiance measurements did not reveal a particular zonation of cyanobacteria, purple or green bacteria in the first millimeter of the mat. Terminal-restriction fragment length polymorphism analysis of PCR-amplified 16S rRNA gene fragments of bacteria depicted the community composition and a fine-scale depth-distribution of at least five different populations of anoxygenic phototrophs and at least three types of sulfate-reducing bacteria along the microgradients of oxygen and light inside the microbial mat.

Biofilms↗