NITZSCHIA OVALIS(BACILLARIOPHYCEAE) MONO LAKE STRAIN ACCUMULATES 1,4/2,5 CYCLOHEXANETETROL IN RESPONSE TO INCREASED SALINITY¹

Abstract

The growth of microalgae in hypersaline conditions requires that cells accumulate osmoprotectants. In many instances, these are polyols. We isolated the diatom Nitzschia ovalis H. J. Arn. from the saline and alkaline water body Mono Lake (CA, USA). This isolate can grow in salinities ranging from 5 to 120 parts per thousand (ppt) of salt but normally at 90 ppt salinity. In this report, we identified the major polyol osmoprotectant as 1,4/2,5 cyclohexanetetrol by electron ionization-mass spectrometry (EI-MS), (1) H, (13) C nuclear magnetic resonance spectroscopy (NMR), and infrared (IR) and showed an increase in cellular concentration in response to rising salinity. This increase in the cyclitol concentration was evaluated by gas chromatography of the derived tetraacetylated cyclohexanetetrol obtaining an average of 0.7 fmol · cell(-1) at 5 ppt and rising to 22.5 fmol · cell(-1) at 120 ppt. The 1,4/2,5 cyclohexanetetrol was also detected in the red alga Porphyridium purpureum. Analysis of the free amino acid content in N. ovalis cultures exposed to changes in salinity showed that proline and lysine also accumulate with increased salinity, but the cellular concentration of these amino acids is about 10-fold lower than the concentration of 1,4/2,5 cyclohexanetetrol. The comparison of amino acid concentration per cell with cyclitol suggests that this polyol is important in compensating the cellular osmotic pressure due to increased salinity, but other physiological functions could also be considered.

Resistance and resilience of benthic biofilm communities from a temperate saltmarsh to desiccation and rewetting

“…First, lower-molecular-weight fixed carbon secreted by the MPB would be used quickly by bacteria (Cook et al, 2007;Hofmann et al, 2009); however, reductions in enzyme activity would cause a net increase in sediment concentrations if 'new' carbohydrate production remained constant. Second, bacteria and diatoms are likely to synthesize organic compatible solutes to protect from desiccation and increased salinity (van Bergeijk et al, 2003;Garza-Sanchez et al, 2009); such compounds can be secreted or leak from cells, and may be liberated by cell lysis of those microbes that are unable to tolerate the increasing osmotic stress. Third, total bacterial mortality in intertidal sediments, potentially from many sources (for example grazing, viral lysis, thermal and salinity stress), has been shown to be the primary fate (up to 65%) of bacterial production (van Oevelen et al, 2006), with the released carbon being recycled back to the DOC pool.…”

Synchronized Regulation of Different Zwitterionic Metabolites in the Osmoadaption of Phytoplankton

“…Organic osmolytes include polyols [2,3], amino acids [4,5] and zwitterionic substances [6,7,8]. Certain zwitterionic metabolites may fulfill multiple physiological roles in algae e.g., as osmolytes, antioxidants and cryoprotectants [9,10,11].…”

Compatible solutes in three marine intertidal microphytobenthic Wadden Sea diatoms exposed to different salinities

“…Besides the free amino acids, several other organic osmolytes have been detected in marine and estuarine diatoms, such as glycine betaine (Dickson & Kirst, 1987b), homarine (Dickson & Kirst, 1987b;Nothnagel, 1995), cyclohexanetetrol (Fujii et al, 1995;Garza-Sa´nchez et al, 2009), glycerol (Dickson & Kirst, 1987b), and finally, mannose (Paul, 1979). While glycerol and mannose are direct products of photosynthesis, like sugars (e.g.…”