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During the first week of our trip, we made an exciting discovery! In one of the ponds in Maiviken Cove, we found cyanobacterial mats.

 

Maiviken is a a beautiful cove on Thather Peninsula,only a 1 hour walk away from KEP. The cyanobacterial mat were in a small pond close to the scree slopes on the eastern side of the valley. The cyanobacterial-based mats were a lot more gelatinous than, for example, mats from the McMurdo Ice Shelf, but nevertheless clearly definiable as lift-off mats of up to 1 cm thickness.

 

Back in the lab, I had a look under the microscope and the mats were comprised of various morphotypes of Oscillatoriales includig Phormidium and Leptolyngbya, the unicellular order Chroococcales as well as Nodularia, which is a genus in the nitrogen-fixing order Nostocales.

 

A few weeks later, I also found cyanobacterial mats with a similar taxa composition in apond in Hapon Bay, which is also on Thather Peninsula. This finding is interesting as there is very little know about mat-forming cyanobacteria from South Georgia. Therefore, we collected material for more detailed microscopic and DNA analyses of the cyanobacterial diversity in these mats.

IMG_8116.jpgCyanbacterial mats in Maiviken Cove

 

On Barff Peninsula, I found a meltwater stream where the cyanobacterial genus Nostoc was growing on some of the rocks. The Nostoc nodules were ca 1 cm in diameter. It was difficult to get a good image beause of the reflection of the sun in the fast flowing water.

IMG_8398.jpgNostoc in a stream on Barff Peninsula

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This afternoon we went for a walk on the Lake Fryxell. The ice is incredible clear in the moat regions, and one can find everywhere cyanobacterial mats frozen into the ice. These cyanobacterial mats were originally from the bottom of the lake, and are called lift-off mats. Microbial mats often drift to the top of the water when they are pushed upwards through the formation of gas bubbles. Although mats are now frozen, it is very likely that many of the cyanobacteria in the mats are still viable.

 

Lake Fryxell with Canada Glacier in the background

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Dried cyanobacterial mats in the ice

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Most of the cyanobacterial mats that we have found were orange pigmented and the macroscopic structure was flaky to cohesive. The orange colour is due to carotenoids which are an protection against UV and oxidative stress.

 

I had a small light micrscope with me in the field and the genus Leptolyngbya dominated the orange mats. Leptolyngbya are filamentous non-branching cyanobacteria belonging to the order Oscillatoriales. They are mostly between 0.5-3 micrometre thick. However, the lower side of the orange layers sometimes had green pigmentation, which besides the Leptolyngbya also had some Phormidium. The genus Phormidium also belong to the order Oscillatoriales, but they are thicker with a width of around 5 micrometres.

 

   Flaky orange-pigmented cyanobacterial mats dominated by Leptolyngbya

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Cohesive orange-pigmented cyanobacterial mats

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green lower side of cyanobacterial mat with Phormidium

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Interestingly, we also found some cyanobacterial mats which were dark purple to black. This colour is due to the UV-screening Scytonemin. We found the genus Schizothrix sp. (Oscillatoriales)  in the mats which is known to produce Scytonemin. We also found several ponds with large accumulations of the genus Nostoc, which belongs to the order Nostocales and has specialist cells called heterocysts for nitrogen-fixation.

 

Cyanobacterial mats with the Scytonemin-producing genus Schizothrix

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Nostoc accumulations in a meltwater pond

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We also found a few ponds with green algae. Green algae biofilms are easy to distinguish from cyanobacteria as green algae are very bright green.

                                                                                              

Green algae

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There are many small ponds and lakes at Cape Evans, similar to Cape Royds . After a quick survey of the ponds, we concentrated on five ponds for sampling. We sampled for morphological, DNA- and RNA-based analysis of the cyanobacterial diversity, as well as nutrient analysis of the water.

 

In one pond we found a pink coloured layer at the bottom of the mats, which is due to the presence of purple bacteria that  are anoxygenic phototrophs.


 



Cyanobacterial mats in Skua Lake

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Large cyanobacterial mat accumulations

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Cyanobacterial mat with a pink layer of purpil bacteria  at the bottom



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Water sampling at a small pond at Cape Evans


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The terrain surounding Cape Royds is covered with many ponds that vary in size, depth, shape and conductivity (salinity). There are also two larger lakes: Blue Lake and Clear lakes that are ice-covered all year. They were named during Shakleton’s expedition because of their blue and clear ice colour.  We were amazed by the variability of pond characteristics and diversity of microbial mats.



Back at the Natural History Museum we will study the cyanobacterial mats using microscopy and DNA-based tools to see if different mat types comprise different cyanobacterial communities.




                                             small pond with lift-off mats at Cape Royds

                                                 

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                                                                 Cyanobacteria-dominated mats

    

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In Lake Hoare the mats are vertically stratified. Each year one layer is formed and they can be used as indicators of growth and environmental conditions just like tree rings. Similar to microbial mats in other lakes the layers have different pigmentations for light capturing and protection.

 

                                                                                Cyanobacterial mats in Lake Hoare

 

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After the divers had brought up mat samples from a depth of ca 10 m, we went back to the lab and identified the diversity using light microscopy. The microbial mats contained different cyanobacteria including the genera Oscillatoria, Phormidium, Leptolyngbya and Nostoc.

 

After returning to the Natural History Museum, we will carry out DNA-based methods to characterise their evolutionary relationship to other Antarctica cyanobacteria.