Sequenced the genome of the amoeba Naegleria gruberi

How was the Earth a billion and a half years ago? And that the organisms inhabiting?

In the long evolutionary path that leads from bacteria to humans, a milestone occurred about 1.5 billion years ago when microbes started to "build" cellular compartments where to store their materials, for example, the DNA inside the nucleus, or end up doing all the machinery energy within mitochondria.

The shape of the vessel Naegleria, with two flagella. The nucleus is stained in blue

Scientists have recently sequenced the genome of a strange single-celled organism called Naegleria gruberi, which is a useful reference to understand the transition from prokaryotes, in which all the proteins necessary for life "float" in a kind of soup inside cell, to eukaryotes, which produce such protein organized in a highly compartmentalized.

The sequence obtained from the Department of Energy Joint Genome Institute (JGI) and analysis by scientists of the 'University of California - Berkeley, University of Lancaster British and other US centers and English, has been published today, March 5, in the journal Cell .

"In a sense, the analysis of the Naegleria genome shows us how it could have been our planet more than a billion years ago, and the type and characteristics of organisms that once lived there," says Simon E. Prochnik, the bioinformatics JGI and Berkeley, and co-author of Cell.

A body from the triple personality: hunt bacteria in the form of amoeba, swims in the form scourged and become dormant in the form of cysts

Naegleria is a common soil amoeba - the sequenced organism was taken from the mud of a eucalyptus grove on the Berkeley campus - that, under stress, quickly grows two flagella, like the tail of a sperm, which he uses to swim in puddles.

Electron micrograph of cysts of Naegleria

It can also assume a third semblance, becoming a hard cyst, which can resist long in the soil until the environment becomes hot and humid enough to enable it to summarize the vegetative form of amoeba.

"This single-celled organism hunting and eating bacteria in the form of amoeba, swims around looking for a better environment in the form scourged, and stops safe waiting for better times in the form of cysts "says Prochnik. "The transformation from amoeba to flagellate cell, like that found in N.gruberi, is very rare event"

Not surprisingly, the genome of this organism possesses many genes that allow these three distinct "identity" were well identified 15,727 protein-coding genes, a large number when you consider that the human being possesses approximately 23000 coding.

Prochnik continues: "Naegleria has a lot of genes because it has a way of life much more complicated than most single-celled organisms (especially pests), which assures him a versatility: Naegleria contains all the genetic information necessary to survive in a large number of different environments and to a wide range of stresses "

The researchers compared the Naegleria genome to the genomes of 16 other eukaryotes, ranging from man to fungi and green plants, as well as other unicellular eukaryotes, and have revealed about 4,000 genes that may have been part of the genome first primitive eukaryote. The number of the identified genes surprised the researchers, because of previous comparisons between eukaryotes and prokaryotes (including parasites) came out a much smaller number of ancestral genes. This probably is related precisely to the fact that parasites living off the backs of their guests, and could lose many of the genes essential to life for an autonomous body, without losing their ability to survive. So the ability to make the comparison with eukaryotic genomes of autonomous bodies, not parasitic as Naegleria, that have retained all their essential genes, allows no doubt a more precise analysis.

Lifestyle complicated and flexible metabolism makes Naegleria able to survive the most adverse conditions

Naegleria is part of a diverse group of microorganisms that includes a cousin, Naegleria fowleri, which can infect humans, leading to an extremely serious disease called primary amoebic meningoencephalitis .

Form of amoeba, Naegleria exposes a series of small pins, just called pseudopodia, which allow it to move during his hunt for other microbes; then when the food runs out, the flagella are synthesized and the cell swims in search of new hunting grounds. The interesting thing is that the two structures are composed of two different proteins essential to cell life even in the more complex eukaryotes: the pseudopodia are composed of actin, tubulin and the scourges of here so that the different expression of one or the other structure depending on the environmental conditions can be very helpful for understanding the way in which parallel systems to actin and tubulin were born and evolved, and still vested with a fundamental importance in eukaryotes.

The study of the genome also reveals how Naegleria can produce energy in a very versatile addition to the classic degradation of glucose, amino acids or fatty acids in the presence of oxygen, in the absence of the latter may use other nutrients to produce energy and hydrogen as a byproduct . As Chlamydomonas alga recently sequenced, Naegleria also uses its metabolic flexibility to survive the temporary and intermittent hypoxia (lack of oxygen) of muddy environments. So the study of the genome of this microorganism, as well as to elucidate the molecular mechanisms of its metabolism, can be very useful to better understand the process of production of hydrogen which, as in other organisms, can be used to produce energy.

Finally Fritz-Laylin, about the potential of the study of genomes, concludes: "By comparing different organisms like Naegleria from all over the evolutionary tree of eukaryotes, we may finally be able to understand where we come from"

Source: University of Berkeley


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