Dark survival strategies in benthic diatoms from polar waters

The microphytobenthos of polar shallow waters is dominated by diatoms, which serve as an important food source for benthic organisms. Due to the excretion of extracellular polymeric substances (EPS) this community stabilizes the sediment. Benthic primary production is in the same range as its pelagic counterpart, although it may only occur at specific times during the polar summer (see also “Biomass, primary production and ecophysiology of the microphytobenthos from the Arctic Kongsfjorden”, KA899/12-1,2,3).

During the polar winter, the diatoms have to cope with a long period of darkness. Since the dark survival strategies of these organisms are almost unstudied, a comprehensive evaluation of the underlying cell biological, biochemical and molecular biological mechanisms will be carried out under laboratory conditions looking at representative species abundant in the Arctic Kongsfjorden, Spitsbergen and the Antarctic Potter Cove.

The features to be studied include the maximum survival period and putative changes in cell biology (macromolecular composition, cellular ultrastructure, viability, activity) and in gene expression (expression of functional genes involved in the degradation of storage products such as chrysolaminaran and lipid droplets).

Recently conducted laboratory experiments showed that these diatoms were able to recover growth after several months of darkness. However, the longer the dark incubation the longer the lag-phase for full recovery of growth. The dark incubated cells remained viable in terms of membrane integrity, but the physiological activity measured as intracellular esterase activity was strongly reduced.

We will look for genes contributing to dark survival in diatoms using a molecular biological approach. The gene-products of putative candidates include a lipase and a glucanase. The storage and use of energy reserves like the carbohydrate chrysolaminaran and lipid droplets are, among others, discussed as a strategy for dark survival.

In addition the effect of temperature on the dark survival capability will be of particular interest in our project referring to an increase in water temperature and climate change. If an increase in water temperature negatively affects the dark survival potential of these benthic primary producers as shown for temperate species, this will have consequences for all higher trophic levels and the ecology of benthic polar ecosystems.



Fig.1:Photography of diatoms. (Courtesy of R. Schumann, University of Rostock)

Scientists

Prof. Dr. Ulf Karsten
University of Rostock, Institute of Biological Sciences, Rostock

PD Dr. Burkhard Becker
University of Köln, Institute of Botany, Köln

Carolin Schlie
University of Rostock, Institute of Biological Sciences, Rostock

Research areas

Kongsfjorden, Svalbard, Spitsbergen (Norway) (79° N, 12° E)
Potter Cove, King George Island (Isla 25 de Mayo), South Shetland Islands, Antarctica (62° S, 58° W)

Publications

Fach B, Woelfel J, Rüdiger F Schumann R, Karsten U, 2009. Ecophysiological performance of benthic diatoms from Arctic waters. In: “Cellular origin, life in extreme habitats and astrobiology –The diatom world” (Eds.: Seckbach J, Kociolek P), COLE Series (submitted)

Homepage

Homepage Rostock
Homepage Köln

Research funding organisation

German Research Foundation

Project number: KA 899/15-1
Funding period: 2009 - 2010