Extreme Hypersaline Research Articles

Adaptations to High Salt in a Halophilic Protist: Differential Expression and Gene Acquisitions through Duplications and Gene Transfers.

The capacity of halophiles to thrive in extreme hypersaline habitats derives partly from the tight regulation of ion homeostasis, the salt-dependent adjustment of plasma membrane fluidity, and the increased capability to manage oxidative stress. Halophilic bacteria, and archaea have been intensively studied, and substantial research has been conducted on halophilic fungi, and the green alga Dunaliella. By contrast, there have been very few investigations of halophiles that are phagotrophic protists, i.e., protozoa. To gather fundamental knowledge about salt adaptation in these organisms, we studied the transcriptome-level response of Halocafeteria seosinensis (Stramenopiles) grown under contrasting salinities. We provided further evolutionary context to our analysis by identifying genes that underwent recent duplications. Genes that were highly responsive to salinity variations were involved in stress response (e.g., chaperones), ion homeostasis (e.g., Na+/H+ transporter), metabolism and transport of lipids (e.g., sterol biosynthetic genes), carbohydrate metabolism (e.g., glycosidases), and signal transduction pathways (e.g., transcription factors). A significantly high proportion (43%) of duplicated genes were also differentially expressed, accentuating the importance of gene expansion in adaptation by H. seosinensis to high salt environments. Furthermore, we found two genes that were lateral acquisitions from bacteria, and were also highly up-regulated and highly expressed at high salt, suggesting that this evolutionary mechanism could also have facilitated adaptation to high salt. We propose that a transition toward high-salt adaptation in the ancestors of H. seosinensis required the acquisition of new genes via duplication, and some lateral gene transfers (LGTs), as well as the alteration of transcriptional programs, leading to increased stress resistance, proper establishment of ion gradients, and modification of cell structure properties like membrane fluidity.

Marine Bacterial and Archaeal Ion-Pumping Rhodopsins: Genetic Diversity, Physiology, and Ecology

The recognition of a new family of rhodopsins in marine planktonic bacteria, proton-pumping proteorhodopsin, expanded the known phylogenetic range, environmental distribution, and sequence diversity of retinylidene photoproteins. At the time of this discovery, microbial ion-pumping rhodopsins were known solely in haloarchaea inhabiting extreme hypersaline environments. Shortly thereafter, proteorhodopsins and other light-activated energy-generating rhodopsins were recognized to be widespread among marine bacteria. The ubiquity of marine rhodopsin photosystems now challenges prior understanding of the nature and contributions of "heterotrophic" bacteria to biogeochemical carbon cycling and energy fluxes. Subsequent investigations have focused on the biophysics and biochemistry of these novel microbial rhodopsins, their distribution across the tree of life, evolutionary trajectories, and functional expression in nature. Later discoveries included the identification of proteorhodopsin genes in all three domains of life, the spectral tuning of rhodopsin variants to wavelengths prevailing in the sea, variable light-activated ion-pumping specificities among bacterial rhodopsin variants, and the widespread lateral gene transfer of biosynthetic genes for bacterial rhodopsins and their associated photopigments. Heterologous expression experiments with marine rhodopsin genes (and associated retinal chromophore genes) provided early evidence that light energy harvested by rhodopsins could be harnessed to provide biochemical energy. Importantly, some studies with native marine bacteria show that rhodopsin-containing bacteria use light to enhance growth or promote survival during starvation. We infer from the distribution of rhodopsin genes in diverse genomic contexts that different marine bacteria probably use rhodopsins to support light-dependent fitness strategies somewhere between these two extremes.

Spatial Distribution and Molecular Diversity of Archaeal Communities in the Extreme Hypersaline Meromictic Brâncoveanu Lake (Transylvanian Basin, Romania)

ABSTRACTDating from the Middle Miocene, the massive halite deposits lying beneath the Transylvanian Basin (Central Romania) have been valuable mineral resources quarried for millennia. Among the numerous hypersaline pit lakes that resulted from this mining, Brâncoveanu Lake is unique by its extreme salinity. Assessment of physicochemical variables, water chemistry and trophic status indicated that Brâncoveanu Lake is a permanently stratified, pH-neutral, NaCl-rich and eutrophied system. We investigated the abundance, molecular diversity and vertical distribution of archaeal community by culture-independent approaches. Additionally, the most relevant environmental parameters shaping the archaeal community composition were evaluated by statistical methods. Archaea appeared to largely outnumber Bacteria; altogether the great prevalence of Halobacteriaceae-related sequences could imply a major contribution of this group to the biogeochemical carbon turnover. The fairly distinct composition of archaeal communities reflects the lake's physicochemical stratification. Among the limnological factors, salinity and oxygen showed a significant impact on determining the composition and structure of archaeal assemblages. Furthermore, Brâncoveanu Lake might harbor novel microorganisms such as members of the recently described phylum Nanohaloarchaea. Overall, this study reported the occurrence of halophilic Archaea in a little explored hydrogeochemical system and provided a better insight into geomicrobiology of meromictic hypersaline pit lakes.

Biotic responses to extreme hypersalinity in an arid zone estuary, South Africa

The Groen Estuary does not function as a typical temporarily open/closed estuary for much of the time, due primarily to the high variability of its physico-chemical attributes. Extreme states are represented by an open mouth following a flood (low salinity) and extreme hypersaline conditions that develop after a prolonged period (years) of mouth closure and a high rate of evaporation from the water body. Available information suggests that biotic recruitment from the marine environment follows mouth breaching, but species disappear progressively as salinity increases and threshold salinity values are reached. A field survey in February 2015 indicated that at the time, salinity ranged from 223 in the lower reaches and <10 upstream over a distance of <1km. The study provided new information on the estuary that includes the revised delineation of the lateral boundary. Habitat mapping from past aerial photographs showed that the open water surface area has decreased over time but the vegetated areas have remained stable. No benthic macroinvertebrates, mesozooplankton or fish were present. Together with low avian species counts and abundance it was concluded that the Groen Estuary represented a small, naturally stressed ecosystem in February 2015. Main stressors were extreme hypersalinity, relatively low water volume, anoxic sediments and a mouth that had remained closed for a relatively long period of time (years).

Population and osmoregulatory responses of a euryhaline fish to extreme salinity fluctuations in coastal lagoons of the Coorong, Australia

River flows and salinity are key factors structuring fish assemblages in estuaries. The osmoregulatory ability of a fish determines its capacity to tolerate rising salt levels when dispersal is unfeasible. Estuarine fishes can tolerate minor fluctuations in salinity, but a relatively small number of species in a few families can inhabit extreme hypersaline waters. The Murray–Darling Basin drains an extensive area of south-eastern Australia and river flows end at the mouth of the River Murray. The system is characterized by erratic rainfall and highly variable flows which have been reduced by intensive river regulation and water extraction. The Coorong is a coastal lagoon system extending some 110 km south-eastwards from the mouth. It is an inverted estuary with a salinity gradient that typically ranges from estuarine to triple that of sea water. Hypersalinity in the southern region suits a select suite of biota, including the smallmouth hardyhead Atherinosoma microstoma – a small-bodied, euryhaline fish with an annual life cycle. The population response of A. microstoma in the Coorong was examined during a period of considerable hydrological variation and extreme salinity fluctuations (2001–2014), and the findings were related to its osmoregulatory ability. Most notably, the species was extirpated from over 50% of its range during four continuous years without river flows when salinities exceeded 120 (2007–2010). These salinities exceeded the osmoregulatory ability of A. microstoma. Substantial river flows that reached the Coorong in late 2010 and continued into 2011 led salinities to fall below 100 throughout the Coorong by January 2012. Subsequently, A. microstoma recovered to its former range by January 2012. The findings show that the consequences of prolonged periods of insufficient river flows to temperate inverted estuaries will include substantial declines in the range of highly euryhaline fishes, which also may have wider ecological consequences.

Effects of hypo- and hypersalinity on photosynthetic performance of Sargassum fusiforme (Fucales, Heterokontophyta)

Photoprotection mechanisms protect photosynthetic organisms, especially under stress conditions, against photodamage that may inhibit photosynthesis. We investigated the effects of short-term immersion in hypo- and hypersalinity sea water on the photosynthesis and xanthophyll cycle in Sargassum fusiforme (Harvey) Setchell. The results indicated that under moderate light [110 μmol(photon) m-2 s-1], the effective quantum yield of PSII was not reduced in S. fusiforme fronds after 1 h in hyposalinity conditions, even in fresh water, but it was significantly affected by extreme hypersalinity treatment (90‰ sea water). Under high light [HL, 800 μmol(photon) m-2 s-1], photoprotective mechanisms operated efficiently in fronds immersed in fresh water as indicated by high reversible nonphotochemical quenching of chlorophyll fluorescence (NPQ) and de-epoxidation state; the quantum yield of PSII recovered during the subsequent relaxation period. In contrast, fronds immersed in 90‰ sea water did not withstand HL, barely developed reversible NPQ, and accumulated little antheraxanthin and zeaxanthin during HL, while recovery of the quantum yield of PSII was severely inhibited during the subsequent relaxation period. The data provided concrete evidence supporting the short-term tolerance of S. fusiforme to immersion in fresh water compared to hypersalinity conditions. The potential practical implications of these results were also discussed.

Preface to the proceedings of Halophiles 2013.

Halophiles are organisms, and their viruses, adapted to thriving and reproducing in high salt concentrations, representatives of which can be found in all domains of life. To flourish in these environments, an individual must overcome many obstacles including high osmotic pressure, low water availability, high and low pH conditions, high temperatures, and high cell densities that enforce stiff competition for limited resources due to the low solubility of gasses and other nutrients. Therefore, all halophiles can be considered poly-extremophiles. These interesting life forms do not cause infectious diseases or cancer, impact human lifestyles or infect our food supply. So why study them? Often halophiles are studied because the salty environment is a model system for uncovering basic principles of microbial life. This extreme environment selects against any organism not able to cope with high salt, which reduces the overall community structure and function. The expectation is that this decrease in complexity allows for more easily achieved insights into fundamental microbial adaptations, and ecological, biogeochemical and evolutionary processes. Because the extreme hypersaline environments are limited to only microbial life, the habitat is analogous to that which existed on Earth before the Cambrian Explosion. Thus investigations of hypersaline habitats can deliver insight into the longest epoch of life. Modern microbial mats growing in hypersaline habitats are similar in structure to ancient stromatolites found in the Precambrian fossil record. Related to this is the search for life in the cosmos: the long period of dominant microbial life on Earth suggests a higher likelihood of finding microbial life on another world than finding advanced life, sentient beings, or even trees. Additionally, the adaptations required for life in high salt can produce enzymes that are interesting for biotechnology, industrial processes, and bioremediation. Every 3 years since the late 1970s halophile researchers who focus on microbial life in hypersaline environments have gathered to present their latest exciting research to like-minded souls. This eBook is a compendium of research written by many of the presenters at Halophiles 2013, the international congress held at the University of Connecticut in Storrs, CT (to view all of the conference oral and poster presentation abstracts, please visit https://www.regonline.com/custImages/250000/250066/Halophiles2013Program_final.pdf). Its range of subject matter is extensive reflecting the 4-day event, and the breadth of research interests. To address this diversity of topics, the chapters are arranged into slightly narrower areas of research interests, but even within these defined partitions the reader will find a wide range of interesting research. Here, we explore the world of halophiles.

Introduction to the Special Issue “Geobiology of Organo- and Biofilms”

Prokaryotic life in present-day extreme environments, e.g., Deep Biosphere, hypersaline environments and many others, is tight-knit with the earliest environmental conditions on earth and therefore...

Genomic adaptations of the halophilic Dead Sea filamentous fungus Eurotium rubrum.

The Dead Sea is one of the most hypersaline habitats on Earth. The fungus Eurotium rubrum (Eurotiomycetes) is among the few species able to survive there. Here we highlight its adaptive strategies, based on genome analysis and transcriptome profiling. The 26.2 Mb genome of E. rubrum shows, for example, gains in gene families related to stress response and losses with regard to transport processes. Transcriptome analyses under different salt growth conditions revealed, among other things differentially expressed genes encoding ion and metabolite transporters. Our findings suggest that long-term adaptation to salinity requires cellular and metabolic responses that differ from short-term osmotic stress signalling. The transcriptional response indicates that halophilic E. rubrum actively counteracts the salinity stress. Many of its genes encode for proteins with a significantly higher proportion of acidic amino acid residues. This trait is characteristic of the halophilic prokaryotes as well, supporting the theory of convergent evolution under extreme hypersaline stress.

English

North of Tunisia consists of numerous ecosystems including extreme hypersaline environments in which the microbial diversity has been poorly studied. The Sehline Sebkha is an important source of salt for food. Due to its economical importance with regards to its salt value, a microbial survey has been conducted. The purpose of this research was to examine the phenotypic features as well as the physiological and biochemical characteristics of the microbial diversity of this extreme ecosystem, with the aim of screening for metabolites of industrial interest. Four samples were obtained from 4 saline sites for physico-chemical and microbiological analyses. All samples studied were hypersaline (NaCl concentration ranging from 150 to 260 g/L). A specific halophilic microbial community was recovered from each site and initial characterization of isolated microorganisms was performed by using both phenotypic and phylogenetic approaches. The 16S rRNA genes from 77 bacterial strains and two archaeal strains were isolated and phylogenetically analyzed and belonged to two phyla Firmicutes and gamma-proteobacteria of the domain Bacteria. The results show that the Sehline Lake harbored novel prokaryotic diversity, never reported before for solar salterns. In addition, diversity measurement indicated an increase of bacterial diversity with rising salinity gradient, which is probably due to competition between bacteria and others species. Key words: Sebkha, bacteria, extremophiles, biodiversity, screening.

Seasonal fluctuations in ionic concentrations drive microbial succession in a hypersaline lake community

Microbial community succession was examined over a two-year period using spatially and temporally coordinated water chemistry measurements, metagenomic sequencing, phylogenetic binning and de novo metagenomic assembly in the extreme hypersaline habitat of Lake Tyrrell, Victoria, Australia. Relative abundances of Haloquadratum-related sequences were positively correlated with co-varying concentrations of potassium, magnesium and sulfate, but not sodium, chloride or calcium ions, while relative abundances of Halorubrum, Haloarcula, Halonotius, Halobaculum and Salinibacter-related sequences correlated negatively with Haloquadratum and these same ionic factors. Nanohaloarchaea and Halorhabdus-related sequence abundances were inversely correlated with each other, but not other taxonomic groups. These data, along with predicted gene functions from nearly-complete assembled population metagenomes, suggest different ecological phenotypes for Nanohaloarchaea and Halorhabdus-related strains versus other community members. Nucleotide percent G+C compositions were consistently lower in community metagenomic reads from summer versus winter samples. The same seasonal G+C trends were observed within taxonomically binned read subsets from each of seven different genus-level archaeal groups. Relative seasonal abundances were also linked to percent G+C for assembled population genomes. Together, these data suggest that extreme ionic conditions may exert selective pressure on archaeal populations at the level of genomic nucleotide composition, thus contributing to seasonal successional processes. Despite the unavailability of cultured representatives for most of the organisms identified in this study, effective coordination of physical and biological measurements has enabled discovery and quantification of unexpected taxon-specific, environmentally mediated factors influencing microbial community structure.

Exploration and characterization of agriculturally and industrially important haloalkaliphilic bacteria from environmental samples of hypersaline Sambhar lake, India

Screening of bacteria from Sambhar lake, an extreme hypersaline environment of India, led to the isolation of 93 haloalkaliphilic bacteria growing optimally in media with 2-25% salt and 6-12 pH. Based on 16S rRNA gene sequences, 93 isolates were further categorized into 32 groups, with each group representing a different taxa belonging to 3 phyla (Firmicutes, Proteobacteria and Actinobacteria). Majority of the isolates (53.12%) showed similarity with phylum Firmicutes which was followed by Proteobacteria (40.63%) and Actinobacteria (6.25%). The isolates belonging to 32 representative groups were further evaluated for the production of extracellular enzymes viz. amylase, cellulase, protease and xylanase, plant growth promoting attributes and BIOLOG™ substrate usage. Among all the isolates, xylanase producing isolates were in maximum (68%) as compared to protease (56%), cellulase (40%), and amylase (37%) producing strains. Similarly, among plant growth promoting activities, ammonia producing isolates were highest (56%) when compared to those producing ACC deaminase (53%), IAA (50%), hydrogen cyanide (28%), siderophore (21%) and solubilizing P (34%). Isolates showing enzymatic and PGP activities could be further utilized for promoting plant growth in saline affected area.

Do Acartia tonsa (Dana) eggs regulate their volume and osmolality as salinity changes?

Subitaneous eggs from an euryhaline calanoid copepod Acartia tonsa were challenged by changes in salinity within the range from full strength salinity, down to zero and up to >70psu. Egg volume changed immediately, increasing from 2.8×10(5)μm(3) at full strength salinity (35psu) to 3.8×10(5)μm(3) at 0psu and back to its initial volume when gradually being returned to full strength salinity. Egg osmolality followed the molality of the surrounding water when challenged within a salinity range from 2 to 50psu. Egg respiration was not affected when eggs kept at 35psu was exposed to low salinity (2psu). These results suggest that eggs are unable to regulate their volume or osmolality when challenged with changes in salinity. Gradual changes in salinity from 35 to 2psu and back did not harm the eggs (embryos), since the hatching success remained unaffected by such changes in salinity. In contrast, extreme hyper-saline conditions (76psu) made the eggs implode and killed the embryo. We propose that the embryo is protected from salinity stress by its plasma membrane and that water exchange driven by osmosis is restricted to the perivitelline space of the egg, which acts as a perfect osmometer in the salinity range of 5-35psu. We hypothesize further that the embryo is able to keep its volume and osmolality constant due to the impermeability of the inner plasma membrane of the egg or by a combination of osmoregulation and reduced permeability of the inner plasma membrane.

Biodegradation of petroleum hydrocarbons in hypersaline environments

Literature on hydrocarbon degradation in extreme hypersaline media presents studies that point to a negative effect of salinity increase on hydrocarbonoclastic activity, while several others report an opposite tendency. Based on information available in the literature, we present a discussion on the reasons that justify these contrary results. Despite the fact that microbial ability to metabolize hydrocarbons is found in extreme hypersaline media, indeed some factors are critical for the occurrence of hydrocarbon degradation in such environments. How these factors affect hydrocarbon degradation and their implications for the assessment of hydrocarbon biodegradation in hypersaline environments are presented in this review.

Unveiling microbial life in the new deep‐sea hypersaline Lake Thetis. Part II: a metagenomic study

So far only little is known about the microbial ecology of Mediterranean deep-sea hypersaline anoxic lakes (DHALs). These brine lakes were formed by evaporite dissolution/brine seeps and are important model environments to provide insights into possible metabolisms and distributions of microorganisms on the early Earth. Our study on the Lake Thetis, a new thalassohaline DHAL located South-East of the Medriff Corridor, has revealed microbial communities of contrasting compositions with a high number of novel prokaryotic candidate divisions. The major finding of our present work is co-occurrence of at least three autotrophic carbon dioxide fixation pathways in the brine-seawater interface that are likely fuelled by an active ramified sulphur cycle. Genes for the reductive acetyl-CoA and reductive TCA pathways were also found in the brine suggesting that these pathways are operational even at extremely elevated salinities and that autotrophy is more important in hypersaline environments than previously assumed. Surprisingly, genes coding for RuBisCo were found in the highly reduced brine. Three types of sulphide oxidation pathways were found in the interface. The first involves a multienzyme Sox complex catalysing the complete oxidation of reduced sulphur compounds to sulphate, the second type recruits SQR sulphide:quinone reductase for oxidation of sulphide to elemental sulphur, which, in the presence of sulphide, could further be reduced by polysulphide reductases in the third pathway. The presence of the latter two allows a maximal energy yield from the oxidation of sulphide and at the same time prevents the acidification and the accumulation of S(0) deposits. Amino acid composition analysis of deduced proteins revealed a significant overrepresentation of acidic residues in the brine compared with the interface. This trait is typical for halophilic organisms as an adaptation to the brine's extreme hypersalinity. This work presents the first metagenomic survey of the microbial communities of the recently discovered Lake Thetis whose brine constitutes one of saltiest water bodies ever reported.

Heart beat rate adaptations to varying salinity of two intertidal Mediterranean bivalves: The invasive Brachidontes pharaonis and the native Mytilaster minimus

Changes in heart beat rates (HBR) of Brachidontes pharaonis (an invasive Lessepsian species) and Mytilaster minimus (a native Mediterranean species) in response to changes in salinity values from brackish (20) to extreme hyper-saline (75) were investigated both in situ and in the laboratory. The two species displayed different responses to varying salinity, with clear differences in HBR observed between groups investigated at different salinities and between groups originating from different environments. The native species, adapted to narrow salinity changes as those observed in the superficial waters of the Mediterranean Sea, showed signs of stress at salinities slightly above 37 (in the range 37–45). On the other hand, the invasive species displayed clear signs of stress only at salinities over 45 and exhibited heart activity even under hyper-saline conditions (i.e. salinity = 75). These results indicate that the Lessepsian species has the potential to invade most of the transitional environments across the entire Mediterranean basin. We therefore stress the need of including Brachidontes pharaonis in all coastal monitoring programmes assessing the actual and potential spreading of alien species in the Mediterranean region.

Biochemical responses of red alga Gracilaria corticata (Gracilariales, Rhodophyta) to salinity induced oxidative stress

The biochemical responses of Gracilaria corticata (J. Agardh) J. Agardh to salinity induced oxidative stress were studied following the exposure to different salinities ranging from 15, 25, 35 (control), 45 to 55 in laboratory conditions. The growth was highest under 25 (3.14 ± 0.69% DGR) and 35 (3.58 ± 0.32% DGR) and decreased significantly in both extreme lower (15) and hyper (55) salinities. Both phycoerythrin (PE) and allophycocyanin (APC) were significantly higher in hyper-salinity (45) with an increase of almost 70% and 52% from their initial contents. Conversely, the level of increase of the same in hypo-salinities was considerably lower as compared with that of hyper-salinity. Both hypo- and hyper-salinity treatments induced almost two fold increase in the contents of polyphenols, proline and the activities of antioxidative enzymes such as superoxide dismutase (SOD), ascorbate peroxidase (APX) and glutathione reductase (GR) especially for 6 d exposure. The Na + ions readily displaced the K + and Ca 2+ from their uptake sites at extreme hyper-salinity (55) and accounted for substantial increase in the ratio of Na +/K + and Na +/Ca 2+ that impeded the growth under long term exposure (> 6 d). The survivability at salinity 45 even with considerably higher ratio of Na +/K + and Na +/Ca 2+ suggests the compartmentalization of Na + into the vacuoles. Further, the micro nutrients such as Zn, Fe and Mn were decreased at both high and low end salinities with highest at extreme hyper-salinity. The C18:1(n−9) cis, C18:2(n−6), C18:3(n−3) and C20:4(n−6) were found in significant amounts in hyper-salinities. The C18:1(n−9) cis in particular increased by 60.25% and 70.51% for salinities 45 and 55, respectively from their initial amounts. The ratio of total unsaturated to saturated fatty acids (UFA/SFA) also increased linearly with increasing salinity. These results collectively suggest the potential role of antioxidative enzymes, phycobiliproteins, PUFAs and mineral nutrients to combat the salinity induced oxidative stress in G. corticata.

Differential expression of the heat shock protein Hsp70 in natural populations of the tilapia, Sarotherodon melanotheron, acclimatised to a range of environmental salinities

BackgroundThe relationship between environmental variation and induction of heat shock proteins (Hsps) has been much documented under experimental conditions. However, very little is known about such induction in natural populations acclimatised to prevailing environmental conditions. Furthermore, while induction of stress proteins has been well documented in response to environmental contaminants and thermal stressors, little is known about whether factors, such as extreme salinity, are also potential inductors. The black-chinned tilapia Sarotherodon melanotheron is unusual for its ability to colonise estuarine environments in West Africa that are characterised by extremely high salinities. The relationships between mRNA levels of the 70 kDa heat shock protein (Hsp70) and Na+, K+-ATPase1α (Naka) in the gills, environmental salinity, and a life-history trait (condition factor) were investigated in wild populations of this species sampled from three locations in the Saloum estuary, at salinities ranging from 40 to 100 psu.ResultsThe highest Hsp70 and Naka mRNA levels, and the poorest condition factors were recorded in the most saline sampling site (100 psu). The Hsp70 and Naka mRNA were correlated amongst themselves and showed a direct positive correlation with environmental salinity, and a negative correlation with fish condition factor. Thus, the Hsp70 is constitutively overexpressed by S. melanotheron acclimatised to extreme hypersalinity.ConclusionsThese results indicate that, although S. melanotheron can colonise extremely saline environments, the overexpression of Hsp70 combined with the higher Naka mRNA expression reveals that this represents a chronic stress. The induction of Hsp70 was, therefore, a biomarker of chronic hyper-osmotic stress which presumably can be linked to the impaired growth performance and precocious reproduction that have been demonstrated in the populations at the extremely saline sites.

Desulfosalsimonas propionicica gen. nov., sp. nov., a halophilic, sulfate-reducing member of the family Desulfobacteraceae isolated from a salt-lake sediment

A novel halophilic Gram-negative sulfate-reducing bacterium affiliated with the deltaproteobacterial family Desulfobacteraceae, strain PropA(T), was isolated from the extreme hypersaline sediment of the northern arm of Great Salt Lake, Utah, USA. Comparative 16S rRNA gene sequence analysis showed that strain PropA(T) is the first cultured representative of a clade of phylotypes that have been retrieved from a range of geographically and ecologically distinct hypersaline environments. Strain PropA(T) shared < or =90 % 16S rRNA gene sequence identity with cultured strains within the family Desulfobacteraceae. Cells of strain PropA(T) were rod-shaped and sometimes motile. The strain required NaCl for growth and grew at salinities up to 200 g NaCl l(-1) (optimum 60 g l(-1)). Growth was observed at 15-40 degrees C, optimum growth occurred at about 40 degrees C, while growth was absent at 10 and 45 degrees C. The pH range for growth was pH 6.0-8.3. Yeast extract (0.1 g l(-1)) was required for growth. C(2-4) alcohols, C(3-4) carboxylic acids, yeast extract and H(2)/acetate supported growth with sulfate as electron acceptor. Sulfate, thiosulfate and sulfite served as electron acceptors, but not elemental sulfur, nitrate or fumarate. The DNA G+C content of strain PropA(T) was 54.1 mol%. Based on the genotypic and physiological properties, we propose that strain PropA(T) represents a novel species within a novel genus, Desulfosalsimonas propionicica gen. nov., sp. nov. The type strain of Desulfosalsimonas propionicica is PropA(T) (=DSM 17721(T) =VKM B-2385(T)).

Characterization of halophiles isolated from solar salterns in Baja California, Mexico

Solar salterns are extreme hypersaline environments that are five to ten times saltier than seawater (150-300 g L(-1) salt concentration) and typically contain high numbers of halophiles adapted to tolerate such extreme hypersalinity. Thirty-five halophile cultures of both Bacteria and Archaea were isolated from the Exportadora de Sal saltworks in Guerrero Negro, Baja California, Mexico. 16S rRNA sequence analysis showed that these cultured isolates included members belonging to the Halorubrum, Haloarcula, Halomonas, Halovibrio, Salicola, and Salinibacter genera and what may represent a new archaeal genus. For the first time, metabolic substrate usage of halophile isolates was evaluated using the non-colorimetric BIOLOG Phenotype MicroArray plates. Unique carbon substrate usage profiles were observed, even for closely related Halorubrum species, with bacterial isolates using more substrates than archaeal cultures. Characterization of these isolates also included morphology and pigmentation analyses, as well as salinity tolerance over a range of 50-300 g L(-1) salt concentration. Salinity optima varied between 50 and 250 g L(-1) and doubling times varied between 1 and 12 h.