IPY

International Polar Year 2007-2008: IPY Polar Night Project (NSF0631659)

Research on the lakes of the McMurdo Dry Valleys (MCM) began with the advent of the International Geophysical Year (IGY) in the late 1950’s. IGY research revealed the physical/chemical nature of the lakes, showed that they were the only year-round liquid water environments on the continent, and inferred that the biological systems in the permanently ice-covered lakes must possess novel physiological strategies that allow them to survive at low temperature and under extended darkness. Although studies during the spring-summer period have yielded a quantum increase in our understanding of the lakes, the unique aspects of physiological adaptation, biodiversity and ecosystem function during the permanently cold and prolonged darkness of the Antarctic winter will never be understood without extended season research. The U.S. component of “International Polar Year 2007-2008” (IPY), through the research initiative “Adaptations to life in extreme cold and prolonged darkness,” provided an important framework in which to study biological adaptation/acclimation by plankton to extreme cold and prolonged darkness at the cellular, genomic and ecosystem level. This project proposed to study lakes within the Taylor Valley during the transition to polar night to test the overarching hypothesis that the onset of darkness induces a cascade of physiological changes that alters the functional roles of autotrophic and heterotrophic microplankton within the lakes. The overarching hypothesis of this project was: Polar night induces a cascade of physiological changes that alters the functional role of autotrophic and heterotrophic microplankton within the lakes. Work in the Morgan-Kiss laboratory specifically addressed two sub-hypotheses: H2-Functional downregulation of the photochemical apparatus during the summer-winter transition is integral to the overwintering strategy of phytoplankton; H3-The photosynthetic process will be structurally altered at the level of gene expression in phototrophic communities during the winter-summer transition.

Experiment Summary

Experiments undertaken by the Morgan-Kiss group were focused on the phytoplankton communities residing in the east and west lobes of Lake Bonney. Data acquisition related to the original sub-hypotheses covered three major experiments:

(i) Adaptation of the model photopsychrophile, Chlamydomonas raudensis UWO241 to polar night.
(ii) Phylogenetic diversity and dynamics of the micro-eukaryotic (the protists) community (18S rRNA).
(iii) Phylogenetic diversity and dynamics of multiple isoforms (rbcL IA/B and ID) of the key enzyme catalyzing inorganic carbon fixation, RubisCO, as well as a gene (psbA) encoding a major photochemistry protein, D1.

In addition, we have tracked diversity of two largely uncharacterized microbial groups in Lake Bonney, Archaea and chemolithoautotrophs, using gene-specific probes for Archaeal 16S rRNA and form II RubisCO (cbbM).

C. raudensis Transplant Experiments

One of the only photoautotrophs to be well studied from the lakes is a Chlamydomonas sp. isolated from East Bonney in 1980s by Priscu and colleagues. More than ten years culturing this organism under controlled laboratory conditions has revealed that the photochemical apparatus if finely adjusted to the extremely stable low light/low temperatures. However, adaptation of a highly efficient photochemical apparatus has been as a consequence of a loss of multiple acclimatory responses. In an effort to enhance our understanding of the physiology of the enigmatic alga, we designed a novel in situ experiment that involved transplanting cultures of C. raudensis back to its native environment and study alterations in its physiology/biochemistry during the transition to complete darkness. Experiments included: • PE: photosynthesis-irradiance curves (Dr. Michael Lizotte)
• Chlorophylls-a and –b, total protein abundance
• Quantification of RbcL (RubisCO), D1 (Photosystem II reaction center), LHC (light harvesting complex II) and phosophoproteins using western blotting
• Gene copy number (DNA) and transcript abundance (mRNA) of rbcL, psbA, and 18S rRNA using real time quantitative PCR

Date Lake Depth (m) Process 23 Feb 08 East Bonney 17 Set-up and T0 samples
1 Mar 08 East Bonney 17 T1 - 2 tubes removed
8 Mar 08 East Bonney 17 T2 - 2 tubes removed
15 Mar 08 East Bonney 17 T3 - 2 tubes removed
22 Mar 08 East Bonney 17 T4 - 2 tubes removed
30 Mar 08 East Bonney 17 End of expt. T5 - 7 tubes removed

Lake Water Collections

Protists play important roles in carbon and nutrient cycling in all aquatic environments. Since the dry valley lakes are almost exclusively dominated by microorganisms, protists species occupy both the base and the top of the dry valley food web. Thus, characterizing the diversity and functional role of this group of microorganisms is critical to understanding food web dynamics in the dry valley lakes. Although a large number of studies have reported on protist diversity in Antarctic aquatic ecosystems, research to date has relied on taxonomic characterization by microscopic identification: no published data currently exists on the phylogenetic diversity of the eukaryotic microorganisms residing in the water column of the lakes. In order to explore protist diversity in the dv lakes 18S rDNA clone libraries from samples collected from ELB and WLB during the transition from Antarctic summer to polar winter. Furthermore, To gain a better understanding of the dynamics of the primary producers of the dry valley microbial food chain during the polar night transition, we monitored via Q-PCR expression levels of rbcL, which encodes for the large subunit of the key enzyme catalyzing CO2 fixation. Experiments included:

• Clone libraries screened by RFLP/sequencing for the following phylogenetic genes: 18S rRNA, archaeal 16S rRNA
• Clone libraries screened by RFLP/sequencing for the following functional genes: rbcL form ID, rbcL form IA/B, psbA, cbbM.
• Gene copy number (DNA) and transcript abundance (mRNA) of rbcL form ID, rbcL form IA/B using real time quantitative PCR
• Transcript abundance of 18S rRNA, archaeal 16S rRNA, psbA and cbbM using real time quantitative PCR

Date Lake Depth (m) Process 24 Feb 08 West Bonney 5,13,15,20 Background filtration for pigments, lipids and molecular assays
25 Feb 08 East Bonney 5,13,18,20 Background filtration for pigments, lipids and molecular assays
2 Mar 08 West Bonney 6,13,15,20 Background filtration for pigments, lipids and molecular assays
2 Mar 08 East Bonney 6,13,18,20 Background filtration for pigments, lipids and molecular assays
9 Mar 08 West Bonney 6,13,15,20 Background filtration for pigments, lipids and molecular assays
9 Mar 08 East Bonney 6,13,18,20 Background filtration for pigments, lipids and molecular assays
16 Mar 08 West Bonney 6,13,15,20 Background filtration for pigments, lipids and molecular assays
16 Mar 08 East Bonney 6,13,18,20 Background filtration for pigments, lipids and molecular assays
24 Mar 08 West Bonney 6,13,15,20 Background filtration for pigments, lipids and molecular assays
24 Mar 08 East Bonney 6,13,18,20 Background filtration for pigments, lipids and molecular assays
29 Mar 08 East Bonney 6,13,18,20 Background filtration for pigments, lipids and molecular assays
30 Mar 08 West Bonney 6,13,15,20 Background filtration for pigments, lipids and molecular assays
10 Apr 08 East Bonney 6,13,18,20 Background filtration for pigments, lipids and molecular assays