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• W1566307983 abstract "Extremes in salinity and temperature and high levels of incident ultraviolet radiation(UVR) characterise the brine pockets and channels of upper Antarctic fast ice. Dataon the composition and distribution of the microbial community inhabiting thisenvironment is limited. Furthermore, how this community tolerates the immoderatephysical and chemical parameters of the upper ice brine is poorly understood.The microbial community in the Davis upper fast ice consists of cryo- andhalotolerant autotrophic flagellates, a few diatoms, one ciliate species and severalheterotrophic species. Small autotrophic dinoflagellates and chrysophytes dominate acommunity containing greater flagellate diversity than previously reported. Acryptomonad and two species of Pyramimonas are reported for the first time.The abundant dinoflagellate of Davis fast ice, identified using molecular taxonomy, isPolarella glacialis Montresor et al. Observations of P. glacialis in this study fromfast and pack ice brine samples along the East Antarctic coastline, with others fromthe literature, indicate that this species has a circumpolar distribution. The perfectmatch between the large subunit ribosomal RNA sequences of the Davis andMcMurdo Sound P. glacialis strains suggests a single Antarctica population of thisspecies.The Davis fast ice brine community shows a remarkable resemblance to that ofMcMurdo Sound. The dominant taxa of the Davis ice, P. glacialis and thechrysophytes, are abundant in McMurdo Sound. These similarities point to at least adisparate distribution of this community throughout Antarctic fast ice. _However, theprobable circumpolar occurrence of P. glacialis and similar taxa from other coastalregions indicate a more continuous fast ice distribution.For the first time, P. glacialis is described in terms of its pigments and lipids. Theextremely high polyunsaturated fatty acid composition of this species (up to 76%)most likely enhances its tolerance of the cold brine environment. The sterol profile ofP. glacialis is atypical of dinoflagellates and is dominated by the 4-desmethylsterol, 27-nor-24-methylcholest-5,22E-3B-ol. This sterol is rare in other dinoflagellates andunknown in other algal classes, suggesting its potential as a biomarker for P. glacialisin the environment. Sediment records of this biomarker may prove useful indetermining past Antarctic climate change and fast ice extent.The upper fast ice of Davis Station is characterised by extreme and transitorysalinities and temperatures over the spring-summer transition. Salinities decreasefrom 96 to 2.5 psu whilst temperatures increase from -4.5 to -0.3 °C. Theseparameters and the relatively high UVR environment of the upper ice are identified asmajor ecophysiological stresses in the brine channels.The osmoregulatory and cryoprotectant role of dimethylsulphoniopropionate (DMSP)in P. glacialis and the Davis fast ice community are investigated in the field and thelaboratory. DMSP concentrations in the brine (450 to 230 nM) decrease in linearproportion to salinity and temperature, implicating DMSP as a possible osmolyte andcryoprotectant. In laboratory studies,. P. glacialis cultures produce up to 47 fMDMSP cell-1. However, under salinity upshock, no clear relationship between DMSPproduction and salinity is evident. Under the nitrogen replete culture conditions usedhere, DMSP is not considered a primary osmolyte in P. glacialis.The effects of UV radiation (280 - 400 nm) on the brine community are assessed insitu using spectral perturbation methods. Under the conditions of this experiment,UV-B radiation (280 - 320 nm) inhibited chl a production within the upper ice whilstUV-A (320 - 400nm) appeared to have little effect. All UV radiation retarded thegrowth of P. glacialis asexual cells, however it is not possible to differentiatebetween the effects of UV-A and UV-B. DMSP concentrations within the brine arereduced under the influence of UV-A alone. UV absorbing compounds, withabsorption. spectra between 310 and 335 nm, are evident in the brine. As lightperturbation did not show trends in the accumulation of these compounds, it isconcluded that the UV absorbing compounds present are not photoinducible." @default.
• W1566307983 created "2016-06-24" @default.
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• W1566307983 date "2000-01-01" @default.
• W1566307983 modified "2023-09-26" @default.
• W1566307983 title "Ecophysiology of the brine dinoflagellate, Polarella glacialis, and Antarctic fast ice brine communities" @default.
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