Scientists from Canada and the United States have isolated a new unicellular anaerobic eukaryote from brackish estuarine sediment collected just below the waterline from Prince Cove, Marstons Mills, Massachusetts.
This is a false-color micrograph of Pygsuia biforma. Scale bar – 2 µm. Image credit: Matthew W. Brown et al / Proc. R. Soc. B.
According to the researchers, the newly discovered species, named Pygsuia biforma, will help them understand the molecular mechanisms and ancestral genetic toolkit that enabled animals and fungi to evolve into diverse, multicellular life forms.
“The importance of this finding is that it helps us decipher how multicellularity evolved. It demonstrates that some genes and proteins that most people think are specific to being multicellular in animals are already present in their unicellular relatives. It is as if the genetic toolkit for becoming multicellular was assembled and modified bit by bit in the single-cell lineages that share a common ancestry with animals,” explained Prof Jeffrey Silberman of the University of Arkansas, co-author of a paper published in the Proceedings of the Royal Society B.
The genus name of Pygsuia biforma is derived from part of the University of Arkansas Razorbacks sports cheer, ‘Wooo Pig Sooie,’ because it has a row of structures resembling the dorsal bristles of razorbacks, which are feral pigs. ‘Pyg‘ replaces ‘pig‘ as a play on the Latin Pygmae, a mythical race of pygmies, a reference to their small size, and ‘sui‘ replaces ‘sooie‘ for brevity and a reference to the animal family to which suids, the ancient biological family of pigs, belong. Consequently the genus name also means ‘little pig‘ in mock Latin.
The species name, biforma, is derived from the presence two distinct cell forms that are observed in the life cycle.
The scientists study the origins and relationships among single-celled eukaryotes, which have nucleus, amoebae and flagellates, some of which are parasites.
“Animals, plants and fungi are all eukaryotes; that is, they have complex cells with organelles such as a nucleus and mitochondria. Eukaryotes and humans have more in common than most people realize,” Prof Silberman said.
The team performs comparative DNA sequence analyses of a type of eukaryote called protists to help find their particular placement or branch on the tree of life. By isolating formerly unexamined anaerobic protists – a diverse group of unicellular microorganisms – and looking at the independent ways they have formed different types of mitochondria, the researchers hope to reveal essential commonalities among all eukaryotes, perhaps even clues that explain their origin.
Genomic analyses of single cell organisms that are specifically related to multicellular lineages often provide clues to understanding the molecular mechanisms involved in the evolution of multi-cellular life.
To characterize Pygsuia biforma, the team described the morphology and sequenced the protein-coding genes of the organism to construct a 159-protein matrix for phylogenetic analyses. Phylogenetics is the study of the evolutionary relationships among groups of organisms.
The researchers found that the organism resembled two types of a breviate, which is a unicellular eukaryote, but distinguished itself with its conspicuous, long flagella.
Most importantly, the phylogenetic tree established the organism as a distant but unequivocal relative to a supergroup of eukaryotes that include fungi and animals. It provides a glimpse of the various components of cell-to-cell adhesion, which is a requirement for multi-cellular organisms.
Pygsuia biforma also possesses components of the integrin-mediated adhesion complex, which in animals plays a key role in cell-to-cell signaling and adhesion to the extracellular matrix.
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Bibliographic information: Matthew W. Brown et al. 2013. Phylogenomics demonstrates that breviate flagellates are related to opisthokonts and apusomonads. Proc. R. Soc. B, vol. 280, no. 1769; doi: 10.1098/rspb.2013.1755
