The change of seasons can be clearly felt in the Alps. Moderate temperatures with high levels of light in summer give way to months of extreme cold and little sunlight in winter. This change can be felt particularly clearly in lakes, because the ice cover lets even less light through.

The bacterial strain Sphingomonas glacialis AAP5 was first discovered in 2013 in Gossenköllesee. Scientists have now discovered that it has adapted to the change of seasons in a special way: the bacterial strain uses two different methods to obtain energy from light. This is reported in a scientific publication that has just been published in the renowned journal “Proceedings of the National Academy of Sciences (PNAS)”. Also on the study, led by Michal Koblížek from the Czech Academy of Sciences, were Christopher Bellas and Ruben Sommaruga from Institute for Ecology at the University of Innsbruck essentially involved. Sommaruga, who is a professor at the institute and leader of the research group “Lake and Glacier Ecology,” explains how the bacterium’s light harvesting works:

Two ways to generate energy

“Light-harvesting bacteria usually only use one of the mechanisms for generating energy from sunlight,” says Sommaruga. “Although genes that contain two light-harvesting mechanisms have already been identified in some bacterial strains, there has been no evidence that a species actually uses both. With Sphingomonas glacialis AAP5, however, we were able to provide this evidence.”

The first mechanism is proton-pumping rhodopsin. These molecules act like a machine powered by light energy, creating a concentration difference of protons between the inside and outside of the bacterium. This difference in concentration then acts as an energy source for the bacterium.

The second mechanism is photosynthesis via bacteriochlorophyll-a. This works in a similar way to plants, which gain from sunlight through the green chlorophyll-a in their leaves. However, photosynthesis with bacteriochlorophyll-a can also absorb light in the long-wave range and produce oxygen (so-called anoxygenic photosynthesis).

Changeable high mountain lakes

To demonstrate the use of both light-harvesting mechanisms in Sphingomonas glacialis AAP5, the researchers grew bacterial cultures under light and darkness conditions and at temperatures between 4°C and 25°C. Using RNA analysis, they examined the activity of genes that are necessary for light collection by rhodopsin or bacteriochlorophyll-a. The experiments showed that in the new bacterium, energy production by bacteriochlorophyll-a takes place at low temperatures and lower light intensities, while the proton-pumping rhodopsins only become active at temperatures below 16°C and with high light intensities.

“The bacterium employs the two light-harvesting mechanisms under very different light and temperature conditions,” says Sommaruga. “We therefore assume that it is an adaptation to the change of seasons and that the bacterium can always use the optimal mechanism, for example when it is currently under ice.”

The limnological research station Gossenköllesee

The Gossenköllesee is a 1.6 hectare high mountain lake at 2,416 m above sea level above the Kühtai saddle in the Stubai Alps. Data has been collected at this lake since 1975, after the original research station at Finstertaler See had to make way for a reservoir project. From 1975 to 2014 the lake was designated as a UNESCO biosphere reserve.

There is one right on the lake Research station of the University of Innsbruck, which was completely renovated in 1994. This is supplied with electricity and water, contains laboratory space, sleeping accommodation for 6 people, kitchen, sanitary facilities, sauna and a storage room. There is a weather station with online transmission on the roof. There is a measuring buoy in the lake, which measures the temperature, pH value, oxygen content and conductivity of the water during the ice-free months. Additional equipment includes boat and diving gear for 2 people.

Current scientific studies at Gossenköllesee deal with various groups of aquatic organisms such as bacteria, flagellates and copepods and their UV protection mechanisms. Atmospheric input and its influence on the water body are also examined. Recent studies are devoted to the discovery and ecology of new viruses in the lake.

In addition to specific research, monitoring programs are also operated at the research station. It is a LTSER (Long-Term Socio Ecological Research) site of the LTSER platform Tyrolean Alps and LTSER Austria and since 2015 a site of GLEON (Global Lake Ecological Observatory Network). It is also a place of training for pupils and students.

Publication:

K. Kopejtka, J. Tomasch, D. Kaftan, AT Gardiner, D. Bína, Z. Gardian, C. Bellas, A. Dröge, R. Geffers, R. Sommaruga, Koblížek , M.: A bacterium from a mountain lake harvests light with both proton-pumping xanthorhodopsins and bacteriochlorophyll-based photosystems. PNAS (2022) https://doi.org/10.1073/pnas.2211018119