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Science News

2 Posts tagged with the cryptomycota tag
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Dr Tom Richards and postdoctoral fellow Dr Meredith Jones, previously of the University of Exeter but now in the Department of Zoology, with Dr David Bass (Zoology) have uncovered a 'missing link' in the fungal tree of life after analysing samples taken from the university's pond. Their study, published in Nature, explains the discovery of a hitherto unknown type of fungi which has fundamentally expanded the scientific understanding of this group of organisms.


"This study has been very surprising -- not least because the original sample came from the nearby pond. Fungi have been well studied for 150 years and it was thought we had a good understanding of the major evolutionary groups, but these findings have changed that radically. Current understanding of fungal diversity turns out to be only half the story -- we've discovered this diverse and deep evolutionary branch in fungi that has remained hidden all this time."

 

The researchers have temporarily named the new group cryptomycota -- which is Greek for 'hidden fungi'. Cryptomycota change the understanding of the whole fungi group because they lack something which was previously considered essential for the classification - a tough cell wall which is important for how fungi feed and grow, breaking down dead animal and plant biomass. Despite lacking the tough cell wall, they seem still to be very successful in the environment because of their extensive diversity and cosmopolitan distribution.

 

"While the first sample used in our investigation was taken from the university pond, Cryptomycota are present in samples taken from all over the world. The huge genetic diversity and prevalence of this group leads us to believe they probably play an important role in a range of environmental processes. It is possible there are many different forms of this organism with a range of characteristics we don't even know about yet. There is a lot more research to be done to find establish how they feed, reproduce, grow, and their importance in natural ecosystems."

 

This study is the result of new efforts to try to understand the diversity of life on Earth by taking DNA sampling out into the field. Until recent years, researchers investigating microbial diversity have sampled by growing microbes in lab cultures, but now it seems that the vast majority of life forms are never captured using these methods -- meaning most of the evolutionary complexity of life remains unsampled. This work was primarily supported by an NERC grant to Tom Richards and is a result of an international collaboration between his group and Dr Ramon Massana's group at the Institut de Ciències del Mar, Barcelona.


MDM Jones, I Forn, C Gadelha, MJ Egan, D Bass, R Massana, TM Richards (2011). Discovery of novel intermediate forms redefines the fungal tree of life. Nature doi:10.1038/nature09984

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Scientists working on the diversity of life are familiar with new estimates of the number of species – we believe that there are around 1.7 million species that have been described over the past three centuries, the vast majority represented in collections such as that of the NHM.  Estimates of the total number of species that actually exist vary hugely, ranging from 10 million to up to 100 million - but the majority certainly seem to be unknown and undescribed. Contrast this with the view in the mid-Eighteenth Century, when Linnaeus thought in terms of the thousands of species that might exist, and was able to describe what he thought was a substantial proportion of life on Earth.

 

We know some groups reasonably well: for example the discovery of new bird species is at a low frequency and mammals similarly so, despite there being a large number of scientists who specialise in these groups.  The situation with invertebrates is rather different – we think that there are millions of undescribed species and the limiting factor is the number of scientists available to find and describe them.

 

But this traditional model is based on knowing that a group exists and (more or less) what a species is in that group– such as beetles, or flowering plants, or nematodes.  When it comes to very small organisms – whether bacteria or other groups, we are much less certain of the overall extent and groupings of natural diversity.

 

Our view has been limited in the past by the need to see the organism or to be able to culture it in a laboratory..  Our understanding now can change rapidly as a result in advances in the use of molecular biological techniques that enable us to look for distinctive DNA or RNA in the environment and compare this with what is already known.

 

A new discovery, led by NHM scientist Tom Richards with David Bass (both in Zoology), and collaborators from Exeter, Cambridge, Barcelona and Harvard, has opened up a new horizon in how we think about fungal diversity (Jones et al., 2011). It could represent the discovery of a new fungal phylum - a major group in taxonomic terms.

 

Fungi are extremely diverse – with traditional estimates of 1.5 million species.  They are more closely related - as a sister group - to animals than to plants and have traditionally been thought to have characteristic cell walls made of chitin or cellulose.  It is thought that plants, animals and fungi all originated from single-celled organisms that used flagellae to propel themselves through water (James et al., 2006).

 

Tom, David and their colleagues took information on known RNA diversity in fungi and compared this with new material from sea and freshwater samples from Devon in the UK.  They found a wide diversity of new RNA profiles for previously unknown organisms that were clearly within the fungi but which were distinctly different from what was already known: the new profles were most similar to a couple of unusual species in the genus RozellaRozella is considered a primitive fungus because it lacks the normally characteristic cell wall (as do the newly discovered fungi) and has represented a tiny and uncharacteristic group in past understanding of fungal diversity.  The lack of a cell wall seems to make these fungi difficult to culture in the laboratory - and so difficult to find.

 

They also found evidence that these new and hidden fungi – which they called Cryptomycota – have three life cycle stages: one a resistant dormant cyst; a second mobile zoospores with flagellae; and a third attached to the cell of another organism (such as diatoms, which are single-celled plants).

 

What does this mean?  These fungi could play a significant part in ecosystems, interacting with other organisms and influencing how those ecosystems work and how other organisms live.  We don’t at this stage know how widespread they are, how diverse they are, or their ecology, but given their diversity it seems possible that they are widespread and their ecology diverse.

 

It also shows that our traditional methods of exploring diversity can miss major groups – if we have not been able to see organisms easily, and they cannot be cultured in the lab, we do not know that they exist, so our estimates of possible diversity could be significantly in error. What else is there to be found?

 

 

James, T. et al. (2006) Reconstructing the early evolution of Fungi using a six-gene phylogeny. Nature 443, 818-822 (19 October 2006) doi:10.1038/nature05110

 

Jones, D.M. et al. (2011) Discovery of novel intermediate forms redefines the fungal tree of life. Nature, Published online 11 May 2011 doi:10.1038/nature09984

 

http://www.nature.com/news/2011/110511/full/news.2011.285.html