Dr. Nuria Gaju and Dr. Mayra Martinez are leading a research group based on environmental microbiology in the Autonomous University of Barcelona. They are studying composition and dynamics of different types of bacterial communities in different types of environments; artificial and natural environments. Basically, they have two main objectives on the research.The first one, is to study the possibilities of improving the management of the best with important economical and agricultural impacts. The second one, is to study how can it be possible the different mediation of the emerging pollutants. So now, we are going to interview Nuria Gaju. Hi, Nuria. Hi. So Nuria, could you explain us which are the organisms that we find in archaea and bacteria groups, and which are the difference between these two groups? Bacteria and archaea are both prokaryotes. The term prokaryotes is referred to unicellular organisms that like membrane-bound nucleus and other membrane-bound organelles. However, they differ enough at the structural, physiological, and genetic level to be placed in separate domains. These domains, bacteria and archaea, are as different from each other as they are from eukaryotes. So which of the three domains archaea, bacteria, and eukaryote, have more biodiversity, more number of species? Can we know the number of species of bacteria in the world? We then know how many species of prokaryotes inhabit the Earth. Nowadays, only a small proportion of prokaryotes can be cultivated in pure cultures, less than one percent. But molecular technologies are helping us to improve our knowledge on microbial diversity. This molecular data showing us that prokaryotes are the most diverse among all organisms. Just to give you some data. At the end of last century, Wiedemann and collaborators made an estimation of the total number of prokaryotes on the Earth, and the number they obtained was 10 to the 30 cells. If we talk in terms of bacterial species, they are describe it 10 to the fourth. But if we want to speculate on the unknown diversity, authors do not arrive to a consensus, and numbers differs from millions to trillions. Could you talk us about the biodiversity of prokaryotes in specific environments like for example, in different types of soils. Imagine a gram of soil, a single gram of wool soil can harbor 10 to the 10 bacterial cells, and species diversity from 10 to the three to 10 to the fourth. But the important question is to document its global distribution. Because in a recent publication, authors studying more than 200 soils around the around the world, they found that only two percent of the bacterial groups accounted for almost half the bacterial diversity. Then although in other environment prokaryotes exhibit high diversity, only a lone number of species are dominant. Nuria, where can we find prokaryotic organisms? Everywhere. We can find prokaryotic organisms everywhere, living at boiling temperatures or even higher in deep-sea thermal vents. At temperatures below freezing in sea ice. Some produce sulfuric nitric acid, many grow without oxygen. The activities of these anaerobic microorganisms are of paramount importance, because they carry out processes that cannot be accomplished by plants, animals, and eukaryotic microorganisms. They are environmentally essential, especially because they often have unique roles in the biogeochemical cycles such as methane production, nitrogen fixation. I would like to emphasize that life in this planet depends to a large extend on this unseen majority, the prokaryotes. So Nuria, thank you for your collaboration. You are welcome. It was a pleasure to participate in this course. Knowing how many species are on the Earth, is one of the most important questions in science. So here in this slide, you can see the results of one study that tried to quantify the species on the Earth. The number of species known is clear, but it is not clear the estimated number of species that are in the world, so this means it's not clear the prediction of how many species are in total. Approximately, it's estimated that we know 15 percent of the species that are really in the world. So in this table you see that it's known around 1.3 millions of species, and it's estimated that there are around 89 millions of species. So the table also shows results for the prokaryotic organisms, and you see that they are low. So the authors of this work, they recognize it discuss in the result section that these values are not right because the model doesn't take into account enough information about the classification of the prokaryotes. Nowadays, we know that it's estimated that that there are millions of species of prokaryotic cells, as we have seen also with the microbiologist. So depending on the models that made the estimations, we will have one's prediction or another. So we have seen the classification of species and we have tried to understand how many species are in the world. Now I would like you to explain, how can we quantify diversity. So basically to quantify diversity, what we do is to use diversity indexes. This is one of the most used techniques to quantify it. A diversity index is a quantitative measure that reflects how many different types are in a dataset or a community, and simultaneously, it takes into account how evenly these species appear or this basic entity appear, so that it explains how they are distributed among these types. A community dominated by one or two species is considered to have less diversity than a community that is dominated by many different species with similar abundances. So I have prepared this slide to show you some basic diversity index that are very used in ecology to study this diversity. The first one is the species richness. So basically is the number of species in the corresponding dataset or community, so you only need to to make a list of the species you find. Then we have other indexes that contain more information. For example, the Shanon diversity index which takes into account the relative abundances of the species. Then the Shanon diversity index is very related to the species evenness because this is basically, how equal the community is numerically and it is calculated dividing the Shanon diversity index by the maximum value of the Shanon diversity index of that community. Finally, there is the Simpson index. This index consider the total number of organisms of a particular species respect to the total number of organisms of all species. So with all these information, we have answered the question what's biodiversity.
