The Role of Microorganisms in Degradation of Spring Algae Blooms
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| License | CC Attribution 3.0 Unported: You are free to use, adapt and copy, distribute and transmit the work or content in adapted or unchanged form for any legal purpose as long as the work is attributed to the author in the manner specified by the author or licensor. | |
| Identifiers | 10.21036/LTPUB10828 (DOI) | |
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Transcript: English(auto-generated)
00:04
Every year in spring you have massive algal blooms in the temperate and polar oceans which vanish after two to three weeks of blooming. The mechanism of this degradation was completely unknown so far and we asked ourselves who is degrading it.
00:20
We focused on the bacterial part of it and the second question was how are they doing it. For tackling the research questions we have chosen a suite of methods. The first one is based on the ribosomal RNA.
00:42
This gives you the phylogenetic distribution of the different bacterial organisms and the nature of the bacterial organisms. This is actually addressing the first research question, who is there and how abundant are they? The ribosomal RNA is a universal marker, gives you the phylogenetic relation of the different organisms present in the water sample.
01:04
The fluorescence in situ hybridization is a method which you can stain the bacteria in a specific manner on the genus level or on the family level. You really can enumerate the different bacterial genera families in the water sample. The second question was what are they doing? This is currently the method of choice, metagenome sequencing.
01:28
You extract the bulk of DNA, sequence it, assemble it into larger pieces and do a gene prediction on these larger pieces. With a comparison of the different databases you can then get a hint on what the gene is coding for and what functions they have in nature basically.
01:47
This is exactly what we want to find out. What we found out was for us quite surprising that not the huge diversity reacted to the phytoplankton biomass but rather a limited number of organisms, of bacteria.
02:08
They all belonged to the flavobacterial group. One of the earlier responders which reacted first to the algae biomass was a group called Formosa. They reacted within a week time and they increased in cell numbers to make up 20% of the whole entire community which was really a lot.
02:33
And then vanished within a week only giving rise to another bacterial group which is called the polaribacter.
02:40
They come later and so on. There were another three, four of different groups responding in tight succession and also in abundances from maybe 1 to 2% up to 20%. And it was really very surprising for us. If we look then into the genomes, the metagenomes of these organisms we could see that there's a clear pattern.
03:06
From the beginning of the bacterial bloom which responded to the phytoplankton bloom basically, that the substrates get more and more complicated. For example, earlier responders had degradation potential for laminarine which
03:22
is a relatively simple polysaccharide of alpha-1,3-connected glycoside. To later organisms like polaribacter they had repertoire for many different polysaccharides like chondroitin sulfide, manan or xylan.
03:40
And it was for us also a clear hint that they are distinct ecological niches that they partition the polysaccharides among them and that each has a certain specialization for a certain group of polysaccharides. Our findings were surprising in that respect that we have found not a zillions of different bacterial organisms and groups but that
04:12
we have found a limited number of genera and families which were obviously solely responsible for the degradation of the algal biomass.
04:21
They were in the flower bacterial group. That was something new but was always postulated at this rather stochastic process that who is their first wins. Actually what we've shown in several years now that is a deterministic process that always the same organisms come up and bloom.
04:44
And this is actually a reason in the second finding what we found that these organisms have a fixed set of polysaccharide degradation enzymes. So we wrote glycosyl butylases that are organized in poles. These are
05:03
large gene sets. They are specific for degradation of a type of polysaccharides. And these polysaccharides were also limited in diversity. So always the same sets came up. So we had the beginning of the bloom was laminarine important and the end of the blooms were the more complicated polysaccharides, the branch polysaccharides important.
05:29
We have 10 to 15 types which are important and then thousands. If you look now in new organisms which were unknown and we find these gene sets for polysaccharide degradation, we could immediately refer them to this function and say, okay, these bacteria must be
05:48
specific growing on laminarine, for example, or on xylem or on mannan, depending on the repertoire what we showed. And this is for us an exciting tool as ecologists that we can predict the ecological role of these bacteria in the environment.
06:01
This is absolutely novel and gives us really new clues on their role. So the next steps what we are currently doing in the lab is to verify the function of the predicted enzymes, what we have from the different organisms.
06:21
For now it's only a comparison to databases and the functions predicted based on bioinformatic measures. But we are more and more now cloning these enzymes and verifying the functions down to even the crystal structure of the individual enzymes. As an ultimate goal we want also to show the function in the environment, in
06:44
the natural environment to sort out specific organisms and see what they are currently expressing. And if they are really working on one or the other polysaccharide and put this together to a bigger picture.