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International Polar Year:
Bacterioplankton genomic adaptations to Antarctic winter

Project description

This project aims to open the doors into understanding the marine bacterioplankton from targeted diversity, genomic, transcriptomic and proteomic perspectives in a seasonal context – which is essential in this high latitude ecosystem. Through a comparative approach in which winter and summertime bacterioplankton will be studied, discoveries of the biological diversity, evolutionary history, physiological capacity, and genes key to survival in the austral winter waters will be made. The results will unravel the story behind the success of the planktonic archaea in winter waters, and test the hypothesis that the majority of the Bacteria are in starvation/survival mode in winter.

Objectives and Hypotheses

Objective 1. Describe the diversity and genomic content of the austral winter bacterioplankton community. The research is initially discovery-based as it promises to offer much in the way of understanding the capabilities of Antarctic bacterioplankton (e.g. extent of photoheterotrophy and chemoautolithotrophy) in winter. We will also be able to test the following hypotheses:

H1: The prokaryotic community has characteristic winter-time bacterial and archaeal populations that are less diverse in Antarctic coastal waters than corresponding assemblages in temperate systems.

H2: The functional capacity of the winter and summer bacterioplankton assemblages, revealed through a genome content survey, reflects specific seasonally-biased adaptations to the Antarctic Ocean ecosystem.

H3: The Antarctic bacterioplankton environmental genome reflects widespread adaptations to permanently cold conditions Antarctic waters regardless of season.

Approach: High throughput SSU rRNA gene and large-contig environmental clone libraries currently being sequenced through an award supported by the DOE Community Sequencing Program (CSP) will provide the data required to test these hypotheses. This program does not award any support to the investigator – all support goes to the sequencing effort conducted at the Joint Genome Center. The CSP-supported efforts will provide about $800,000 in sequencing and library preparation services comprising:

Objective 2. Investigate the winter-time metabolism and growth dynamics of Antarctic marine bacterioplankton populations in order to understand the specific adaptations key to survival. This objective draws upon discovery based and hypothesis-driven science. The hypotheses to be tested are:

H1: Bacteria respond to the onset of Austral winter by transitioning into the starvation-survival mode.

H2: Bacteria can be recovered into metabolically-active populations from the starvation-survival state by illuminating samples and stimulating phytoplankton blooms and/or by adding organic matter in experimental treatments (i.e., an experimentally-imposed seasonal transition from “winter” to “summer” conditions). This will result in competitive dominance by Bacteria which outgrow Archaea.

H3: Planktonic marine crenarchaeota possess adaptations for enhanced growth and survival in the Austral winter, enabling them to become a dominant part of the picoplankton community.

Approach: We propose to study the bacterioplankton community in situ and in experimental mesocosms during an austral winter field season at Palmer Station.

  1. The bacterioplankton community will be profiled along with environmental parameters to determine abundance, activity and diversity.
  2. The winter-time bacterioplankton transcriptome will be characterized by hybridizing mRNA to microarrays designed from the Antarctic bacterioplankton environmental genome sequence data. Simultaneously, samples will be collected for Antarctic Ocean proteomics studies which aim to detect proteins expressed and essential for survival during winter.
  3. Targeted archaeal and bacterial populations suspected to be important in the bacterioplankton will be studied using microautoradiography-fluorescent in situ hybridization (MAR-FISH), Q-PCR and Q-RT-PCR of SSU rRNA and stress-response genes to determine specific activities of organisms suspected to be thriving in winter conditions.