02573nas a2200265 4500008004100000022001400041245010400055210006900159260001200228300001400240490000700254520177600261653002002037653002102057653001502078653001702093653002402110653001202134653002502146100001202171700002002183700001602203700002902219856005902248 2019 eng d a0948-305500aDrivers of protistan community autotrophy and heterotrophy in chemically stratified Antarctic lakes0 aDrivers of protistan community autotrophy and heterotrophy in ch c01/2019 a225 - 2390 v823 a

Single-celled, eukaryotic microorganisms, known as protists, are responsible for 2 important, yet opposing, metabolic activities within aquatic food webs. They are major primary producers and highly active predators in marine and fresh water systems. While genomics has accelerated in recent years for this taxonomically diverse group, our understanding of the metabolic capabilities of most protists remains limited. It is also poorly understood how protist trophic mode is affected by biotic and abiotic factors, and therefore it is difficult to predict how events such as global climate change will affect the balance between autotrophic and heterotrophic activities in protist communities. To address open questions regarding how protist metabolic versatility is influenced by their environment, we characterized the potential for carbon fixation versus organic carbon degradation using enzymatic assays (RubisCO and β-D-glucosaminidase, respectively) within the water columns of ice-covered lakes in McMurdo Dry Valleys (MDV), Antarctica. Steep physical and chemical gradients in the water columns, microorganism domination and minimal allochthonous inputs makes the MDV lakes uniquely suited to investigate environment-microbe interactions. Spatial trends in RubisCO and β-D-glucosaminidase activities were lake-specific and vertically stratified within the water columns. Moreover, bottom-up drivers controlling the activity of C-fixation vs. organic C-degradation among the MDV protist communities were distinct between the upper photic vs. the deep, aphotic zones. We conclude that differential controls over major C-cycling enzymes have important implications on the influence of environmental change on the carbon and nutrient cycles in the MDV lakes.

10aAntarctic lakes10aAquatic protists10aAutotrophy10aHeterotrophy10aMcMurdo Dry Valleys10aRubisCO10aβ-D-glucosaminidase1 aLi, Wei1 aDolhi-Binder, J1 aCariani, ZE1 aMorgan-Kiss, Rachael, M. uhttps://www.int-res.com/abstracts/ame/v82/n3/p225-239/02158nas a2200229 4500008004100000245010300041210006900144260003900213490000900252520137700261653001001638653002801648653003801676653002401714653001901738653001801757653002301775653001601798100001601814700002901830856006901859 2019 eng d00aImpact of simulated polar night on Antarctic mixotrophic and strict photoautotrophic phytoplankton0 aImpact of simulated polar night on Antarctic mixotrophic and str aOxford, OHbMiami Universityc20180 vM.S.3 a

Phytoplankton in polar regions experience long periods of continuous darkness annually during the polar night. Due to difficulties in performing field work during this period, it is largely unknown how phytoplankton endure this extreme transition from 24-hour daylight in the fall to several months of total darkness in the austral winter. The primary goal of this study was to compare physiological and photosynthetic responses of several Antarctic phytoplankton of variable trophic abilities (pure photosynthetic vs. mixotrophic) to simulated polar night conditions, including the transition seasons before and after winter. Two distinct responses were observed to extended darkness: (1) strict photoautotrophs (Chlamydomonas sp. ICE-MDV and Chlamydomonas sp. UWO241) exhibited functional downregulation their photosynthetic processes in the winter, followed by a lag phase of several days during mimicked spring, and (2) mixotrophs (Isochrysis sp. MDV and Geminigera cryophila) maintained functional photosynthetic apparatus, increased heterotrophy through the winter, and exhibited immediate growth upon return to light incubation. These differing responses to mimicked polar night conditions could represent two different strategies for surviving the long period of darkness in the phytoplankton’s natural environment.

10aalgae10aAntarctic phytoplankton10achlorophyll fluorescence analysis10aMcMurdo Dry Valleys10aPhotosynthesis10aphytoplankton10apolar microbiology10apolar night1 aCariani, ZE1 aMorgan-Kiss, Rachael, M. uhttp://rave.ohiolink.edu/etdc/view?acc_num=miami1547204599969081