Follow up interview with Stefan Leuko

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Results of sampling in Shark Bay

This is a transcript of a QuickTime movie (11.0 MB) recorded in May 2006. Stefan Leuko, from the Australian Centre for Astrobiology, discusses some of the results obtained from samples collected at Shark Bay in 2005.


While we were out at Shark Bay you took a lot of samples of the microbial mats, the smooth mats and the pustular mats, and also of the stromatolites and at different levels of the stromatolites, so can you comment on the results that you’ve had so far at these early stages?

Yes, we were quite lucky actually with the samples we took. They were quite diverse, (which is) what we actually hoped for. So we basically analysed them. We were culturing. We were culturing independent methods. We did molecular profiling with all the samples we’ve got. We’ve got interesting results. We’ve found novel species of halophilic archaea as well as we’ve found novel species of cyanobacteria. We are still, as I said before and last year in the field, we are trying to find out the distribution of the cyanobacteria. We’ve made great progress with that from the samples I took actually in Shark Bay. So we are quite happy with our samples. We found lots of new and interesting things and we hope it’s getting us closer to find out how life might have evolved 3.5 billion years ago.

Was there any difference in what you found in the smooth mats and the pustular mats or were they the same?

No, the smooth mats were a little bit less diverse than the pustular mats. One reason could be that it’s mostly overlaid with water, so there’s lots of water influx, which is not favourable for many of the bacteria, halophiles and cyanobacteria. And so the smooth mat is more, don’t give that much protection from the water, not like a pustular mat with all the little kind of stones and rocks within. So we think that the pustular mat actually gives them more protection from water, sunlight and so the bacteria and cyanobacteria can evolve in there much better than on the smooth mat.

We saw a lot of stromatolites that were a browny colour and some of them were black and the ones that were red, they thought were dead. Did you see any evidence for that in the samples that you took or did you only take samples from the ones that were living in the water?

No, actually, although it looks dead on the outside it’s still alive on the inside so the outer crust is actually just a protection, I guess, from the sun.

Even the red ones?

Even the red ones. We found lots and lots of cyanobacteria in there. They might be just in a dormant state and just wait for more favourable conditions to arise again. So even the rock solid top of a stromatolite contained lots and lots of actually live organisms, which we were able to cultivate and are still working on, actually.

Inside the stromatolite, quite a long way inside it, do you think you would find any, I know you didn’t take samples from there, but from what you’ve seen, do you think you would find any living organisms right inside?

Almost certainly. I think the whole stromatolite is one big living organism although it might not look like on the top because it’s a hard crust but still just a millimetre under the crust you find a huge diversity of different organisms living in there and thriving in this environment and just getting the nutrients from the sea water coming in or maybe some other high community systems, which we don’t know yet but it would be really interesting to get a whole stromatolite sample from the core and see if there is any diversity, difference in there or is it the same at the outside. I think it might be a big difference in the inside.

And was there anything that you were surprised about in the samples that you returned, anything that surprised you or other scientists who’ve looked at them?

Basically the diversity surprised us a little bit. We thought because it’s kind of a harsh environment with lots of UV and high salt, it’s twice the salinity of the normal sea water, we thought that the diversity was less actually rather than we expected. We found lots of new cyanobacterias, which are not yet known. At the moment the lab are working with us in the way to characterise them and basically understand what makes a stromatolite a stromatolite with this diversity and how do the bacteria actually work together.

The bacteria in the mats and in the stromatolites that have formed the mushroom and the club shapes in the water, were they the same sorts of bacteria?

Yeah, they all belong to the same sort of bacteria, it’s mostly cyanobacteria by trapping and binding little sands to build the stromatolite over the time. So even though it was a different kind of sample site, it was still the same basically bacteria and micro organisms are actually present in this environment.

But we still don’t know why some of them remain as mats and others form the shapes?

That is still a question to be answered.




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