This is an RSS newsfeed from BioMed Central It is intended to be used with an RSS reader. For more information about RSS newsfeeds from BioMed Central, visit http://www.biomedcentral.com/info/about/rss/ http://www.salinesystems.org The latest articles from Saline Systems (ISSN 1746-1448) published by BioMed Central Seasonal changes in freshwater phytoplankton communities have been extensively studied, but key drivers of phytoplankton in saline lakes are currently not well understood. Comparative lake studies of 19 prairie saline lakes in the northern Great Plains (USA) were conducted in spring and summer of 2004, with data gathered for a suite of limnological parameters. Nutrient enrichment assays for natural phytoplankton assemblages were also performed in spring and summer of 2006. Canonical correspondence analysis of 2004 data showed salinity (logCl), nitrogen, and phosphorus (N:P ratios) to be the main drivers of phytoplankton distribution in the spring, and phosphorus (C:P ratios), iron (logTFe), and nitrogen (logTN) as important factors in the summer. Despite major differences in nutrient limitation patterns (P-limitation in freshwater systems, N-limitation in saline systems), seasonal patterns of phytoplankton phyla changes in these saline lakes were similar to those of freshwater systems. Dominance shifted from diatoms in the spring to cyanobacteria in the summer. Nutrient enrichment assays (control, +Fe, +N,+P, +N+P) in 2006 indicated that nutrient limitation is generally more consistent within lakes than for individual taxa across systems, with widespread nitrogen and secondary phosphorus limitation. Understanding phytoplankton community structure provides insight into the overall ecology of saline lakes, and will assist in the future conservation and management of these valuable and climatically-sensitive systems. http://www.salinesystems.org/content/5/1/1 Courtney R Salm, Jasmine E Saros, Callie S Martin and Jarvis M Erickson Saline Systems 2009, 5:1 2009-01-05 doi:10.1186/1746-1448-5-1 Saline Systems 1746-1448 5 1 2009-01-05 Trehalose in ectoderms functions in energy metabolism and protection in extreme environmental conditions. We structurally characterized trehalose 6-phosphate synthase (TPS) from hemocytes of the blue crab, Callinectes sapidus. C. sapidus Hemo TPS (CasHemoTPS), like insect TPS, encodes both TPS and trehalose phosphate phosphatase domains. Trehalose seems to be a major sugar, as it shows higher levels than does glucose in hemocytes and hemolymph. Increases in HemoTPS expression, TPS enzyme activity in hemocytes, and hemolymph trehalose levels were determined 24 h after lipopolysaccharide challenge, suggesting that both TPS and TPP domains of CasHemoTPS are active and functional. The TPS gene has a wide tissue distribution in C. sapidus, suggesting multiple biosynthetic sites. A correlation between TPS activity in hemocytes and hemolymph trehalose levels was found during the molt cycle. The current study provides the first evidence of presence of trehalose in hemocytes and TPS in tissues of C. sapidus and implicates its functional role in energy metabolism and physiological adaptation. http://www.salinesystems.org/content/4/1/18 J Sook Chung Saline Systems 2008, 4:18 2008-12-12 doi:10.1186/1746-1448-4-18 Saline Systems 1746-1448 4 18 2008-12-12 Background: Cyclotella choctawhatcheeana Prasad 1990 is a small centric diatom found in the plankton of water bodies with a wide range of salt concentrations. This paper describes the morphological features of the valve of C. choctawhatcheeana, from Alchichica lake, a hyposaline lake located in Central Mexico, and provides information about their ecology with respect to water chemistry and distribution in the water column along the annual cycle. Alchichica, and their neighbor lake Atexcac, are the only Mexican water bodies where C. choctawhatcheeana has been registered. Results: Morphological differences were found with respect to the original description. The valves of C. choctawhatcheeana from Alchichica exceeded the diameter (5-12 mum) given for the type material (3.0-9.5 mum), and it does not forms or seldom forms short chains (2-3 cells) in contrast of up to 20 cell chains. Other difference was the presence of irregularly distributed small silica granules around the margin of the external view of the valve, meanwhile in Prasad's diagnosis a ring of siliceous granules is present near the valve margin; all other features were within the range of variation of the species. Maximum densities (up to 3877 cells ml-1) of C. choctawhatcheeana were found in Alchichica lake from June to October, along the stratificated period of the lake. Low densities (48 cells ml-1) when the water column was mixed, in January and February. C. choctawhatcheeana of Lake Alchichica was found in an ample depth range from 20 m down to 50 m. Conductivity (K25) ranged between 13.3 and 14.5 mS cm-1 and the pH between 8.8 and 10.0. Water temperature fluctuated between 14.5 and 20 oC. Dissolved oxygen ranged from anoxic (non detectable) up to saturation (7 mg l-1). Conclusion: The morphology of C. choctawhatcheeana from Alchichica corresponded to the original description, with exception of some secondary traits. C. choctawhatcheeana can grow in several different environmental conditions. It can use nutrients along the water column during the mixing period in the lake. But when nutrients are scarce, C. choctawhatcheeana, can be located in very high densities, into a well defined depth layer of the lake, being an important contributor to the depth chlorophyll maximum (DCM). The species seems to be a small size but significant component of the phytoplankton in the saline Mexican lake Alchichica. http://www.salinesystems.org/content/4/1/17 Maria Guadalupe Oliva, Alfonso Lugo, Javier Alcocer and Enrique A. Cantoral-Uriza Saline Systems 2008, 4:17 2008-12-08 doi:10.1186/1746-1448-4-17 Saline Systems 1746-1448 4 17 2008-12-08 Haloarchaeal strains require high concentrations of NaCl for their growth, with optimum concentrations of 10–30%. They display a wide variety of morphology and physiology including pH range for growth. Many strains grow at neutral to slightly alkaline pH, and some only at alkaline pH. However, no strain has been reported to grow only in acidic pH conditions within the family Halobacteriaceae.In this study, we isolated many halophiles capable of growth in a 20% NaCl medium adjusted to pH 4.5 from 28 commercially available salts. They showed growth at pH 4.0 to 6.5, depending slightly on the magnesium content. The most acidophilic strain MH1-52-1 isolated from an imported solar salt (pH of saturated solution was 9.0) was non-pigmented and extremely halophilic. It was only capable of growing at pH 4.2–4.8 with an optimum at pH 4.4 in a medium with 0.1% magnesium chloride, and at pH 4.0–6.0 (optimum at pH 4.0) in a medium with 5.0% magnesium. The 16S rRNA and DNA-dependent RNA polymerase subunit B' gene sequences demonstrated clearly that the strain MH1-52-1 represents a new genus in the family Halobacteriaceae. http://www.salinesystems.org/content/4/1/16 Hiroaki Minegishi, Toru Mizuki, Akinobu Echigo, Tadamasa Fukushima, Masahiro Kamekura and Ron Usami Saline Systems 2008, 4:16 2008-10-29 doi:10.1186/1746-1448-4-16 Saline Systems 1746-1448 4 16 2008-10-29 Since its discovery in 1998, representatives of the extremely halophilic bacterium Salinibacter ruber have been found in many hypersaline environments across the world, including coastal and solar salterns and solar lakes. Here, we review the available information about the distribution, abundance and diversity of this member of the Bacteroidetes. http://www.salinesystems.org/content/4/1/15 Josefa Antón, Arantxa Peña, Fernando Santos, Manuel Martínez-García, Philippe Schmitt-Kopplin and Ramon Rosselló-Mora Saline Systems 2008, 4:15 2008-10-28 doi:10.1186/1746-1448-4-15 Saline Systems 1746-1448 4 15 2008-10-28 Chromohalobacter salexigens, a Gammaproteobacterium belonging to the family Halomonadaceae, shows a broad salinity range for growth. Osmoprotection is achieved by the accumulation of compatible solutes either by transport (betaine, choline) or synthesis (mainly ectoine and hydroxyectoine). Ectoines can play additional roles as nutrients and, in the case of hydroxyectoine, in thermotolerance. A supplementary solute, trehalose, not present in cells grown at 37°C, is accumulated at higher temperatures, suggesting its involvement in the response to heat stress. Trehalose is also accumulated at 37°C in ectoine-deficient mutants, indicating that ectoines suppress trehalose synthesis in the wild-type strain. The genes for ectoine (ectABC) and hydroxyectoine (ectD, ectE) production are arranged in three different clusters within the C. salexigens chromosome. In order to cope with changing environment, C. salexigens regulates its cytoplasmic pool of ectoines by a number of mechanisms that we have started to elucidate. This is a highly complex process because (i) hydroxyectoine can be synthesized by other enzymes different to EctD (ii) ectoines can be catabolized to serve as nutrients, (iii) the involvement of several transcriptional regulators (σS, σ32, Fur, EctR) and hence different signal transduction pathways, and (iv) the existence of post-trancriptional control mechanisms. In this review we summarize our present knowledge on the physiology and genetics of the processes allowing C. salexigens to cope with osmotic stress and high temperature, with emphasis on the transcriptional regulation. http://www.salinesystems.org/content/4/1/14 Carmen Vargas, Montserrat Argandoña, Mercedes Reina-Bueno, Javier Rodríguez-Moya, Cristina Fernández-Aunión and Joaquín J Nieto Saline Systems 2008, 4:14 2008-09-15 doi:10.1186/1746-1448-4-14 Saline Systems 1746-1448 4 14 2008-09-15 Background: Most studies of the transcriptional response to UV radiation in living cells have used UV doses that are much higher than those encountered in the natural environment, and most focus on short-wave UV (UV-C) at 254 nm, a wavelength that never reaches the Earth's surface. We have studied the transcriptional response of the sunlight-tolerant model archaeon, Halobacterium sp. NRC-1, to low doses of mid-wave UV (UV-B) to assess its response to UV radiation that is likely to be more biologically relevant. Results: Halobacterium NRC-1 cells were irradiated with UV-B at doses equivalent to 30 J/m2 and 5 J/m2 of UV-C. Transcriptional profiling showed that only 11 genes were up-regulated 1.5-fold or more by both UV-B doses. The most strongly up-regulated gene was radA1 (vng2473), the archaeal homologue of RAD51/recA recombinase. The others included arj1 (vng779) (recJ-like exonuclease), top6A (vng884) and top6B (vng885) (coding for Topoisomerase VI subunits), and nrdJ (vng1644) (which encodes a subunit of ribonucleotide reductase). We have found that four of the consistently UV-B up-regulated genes, radA1 (vng2473), vng17, top6B (vng885) and vng280, share a common 11-base pair motif in their promoter region, TTTCACTTTCA. Similar sequences were found in radA promoters in other halophilic archaea, as well as in the radA promoter of Methanospirillum hungatei. We analysed the transcriptional response of a repair-deficient ΔuvrA (vng2636) ΔuvrC (vng2381) double-deletion mutant and found common themes between it and the response in repair proficient cells. Conclusion: Our results show a core set of genes is consistently up-regulated after exposure to UV-B light at low, biologically relevant doses. Eleven genes were up-regulated, in wild-type cells, after two UV-B doses (comparable to UV-C doses of 30 J/m2 and 5 J/m2), and only four genes were up-regulated by all doses of UV-B and UV-C that we have used in this work and previously. These results suggest that high doses of UV-C radiation do not necessarily provide a good model for the natural response to environmental UV. We have found an 11-base pair motif upstream of the TATA box in four of the UV-B up-regulated genes and suggest that this motif is the binding site for a transcriptional regulator involved in their response to UV damage in this model archaeon. http://www.salinesystems.org/content/4/1/13 Ivan Boubriak, Wooi Loon Ng, Priya DasSarma, Shiladitya DasSarma, David J Crowley and Shirley J McCready Saline Systems 2008, 4:13 2008-08-29 doi:10.1186/1746-1448-4-13 Saline Systems 1746-1448 4 13 2008-08-29 Transcription of the ectoine biosynthesis genes ectA, ectB and ectC from Marinococcus halophilus in recombinant Escherichia coli DH5α is probably initiated from three individual σ70/σA-dependent promoter sequences, upstream of each gene. Consequently, mRNA-fragments containing the single genes and combinations of the genes ectA and ectB or ectB and ectC, respectively, could be detected by Northern blot analysis. Under the control of its own regulatory promoter region (ectUp) a seemingly osmoregulated ectoine production was observed. In addition, aspartate kinases were identified as the main limiting factor for ectoine production in recombinant E. coli DH5α. Co-expression of the ectoine biosynthesis genes and of the gene of the feedback-resistant aspartate kinase from Corynebacterium glutamicum MH20-22B (lysC) led to markedly increased production of ectoine in E. coli DH5α, resulting in cytoplasmic ectoine concentrations comparable to those reached via ectoine accumulation from the medium. http://www.salinesystems.org/content/4/1/12 Thorsten Bestvater, Petra Louis and Erwin A Galinski Saline Systems 2008, 4:12 2008-08-29 doi:10.1186/1746-1448-4-12 Saline Systems 1746-1448 4 12 2008-08-29 The significance of the transport of nutrient-rich hypolimnetic water via the benthic boundary layer (BBL) to the productivity of Mono Lake was studied using a coupled hydrodynamic and ecological model validated against field data. The coupled model enabled us to differentiate between the role of biotic components and hydrodynamic forcing on the internal recycling of nutrients necessary to sustain primary productivity. A 4-year period (1991–1994) was simulated in which recycled nutrients from zooplankton excretion and bacterially-mediated mineralization exceeded sediment fluxes as the dominant source for primary productivity. Model outputs indicated that BBL transport was responsible for a 53% increase in the flux of hypolimnetic ammonium to the photic zone during stratification with an increase in primary production of 6% and secondary production of 5%. Although the estimated impact of BBL transport on the productivity of Mono Lake was not large, significant nutrient fluxes were simulated during periods when BBL transport was most active. http://www.salinesystems.org/content/4/1/11 Louise C Bruce, Robert Jellison, Jörg Imberger and John M Melack Saline Systems 2008, 4:11 2008-08-19 doi:10.1186/1746-1448-4-11 Saline Systems 1746-1448 4 11 2008-08-19 Background: Extracellular dissolved DNA has been demonstrated to be present in many terrestrial and aquatic environments, actively secreted, or released by decaying cells. Free DNA has the genetic potential to be acquired by living competent cells by horizontal gene transfer mediated by natural transformation. The aim of this work is to study the persistence of extracellular DNA and its biological transforming activity in extreme environments like the deep hypersaline anoxic lakes of the Mediterranean Sea. The brine lakes are separated from the upper seawater by a steep chemocline inhabited by stratified prokaryotic networks, where cells sinking through the depth profile encounter increasing salinity values and osmotic stress. Results: Seven strains belonging to different taxonomic groups isolated from the seawater-brine interface of four hypersaline lakes were grown at medium salinity and then incubated in the brines. The osmotic stress induced the death of all the inoculated cells in variable time periods, between 2 hours and 144 days, depending on the type of brine rather than the taxonomic group of the strains, i.e. Bacillaceae or gamma-proteobacteria. The Discovery lake confirmed to be the most aggressive environment toward living cells. In all the brines and in deep seawater dissolved plasmid DNA was substantially preserved for a period of 32 days in axenic conditions. L'Atalante and Bannock brines induced a decrease of the supercoiled form up to 70 and 40% respectively; in the other brines only minor changes in plasmid conformation were observed. Plasmid DNA after incubation in the brines maintained the capacity to transform naturally competent cells of Acinetobacter baylii strain BD413. Conclusion: Free dissolved DNA is likely to be released by the lysis of cells induced by osmotic stress in the deep hypersaline anoxic lakes. Naked DNA was demonstrated to be preserved and biologically active in these extreme environments, and hence could constitute a genetic reservoir of traits acquirable by horizontal gene transfer. http://www.salinesystems.org/content/4/1/10 Sara Borin, Elena Crotti, Francesca Mapelli, Isabella Tamagnini, Cesare Corselli and Daniele Daffonchio Saline Systems 2008, 4:10 2008-08-05 doi:10.1186/1746-1448-4-10 Saline Systems 1746-1448 4 10 2008-08-05