Faculty of Natural and Agricultural Sciences
School of Biological Sciences
Department of Microbiology and Plant Pathology
Selected Highlights from Research Findings
A bacterial disease is causing severe losses to seedlings and cuttings of a Eucalyptus grandis x E. nitens hybrid in South African forestry nurseries. Research findings indicated that this disease, commonly referred to as bacterial blight and dieback, is caused by Pantoea ananatis. It is extremely difficult, using conventional identification techniques, to distinguish this bacterium from other species of the genus Pantoea.
The researchers have developed a diagnostic method, based on Amplified Fragment Length Polymorphisms (AFLPs), to accurately and rapidly distinguish between the six species and two subspecies in the genus.
Prof TA Coutinho
Microbiology and Plant Pathology
+27 (0) 12 420 3934
teresa.coutinho@up.ac.za
The fact that animals and fungi are each other’s closest relatives represents one of the major discoveries of the early nineties. This assemblage, designated the super-kingdom Opisthokonta, has since been expanded to include a number of single-celled eukaryotes (protozoa) that include chaonoflagellates (aquatic protozoa with single flagella and typical collars of tentacles) ministeriids (stalked or free-living amoebae with symmetrically-distributed, radiating pseudopodia), ichthyosporea (fungus-like animal parasites that are either amoeboid or uniflagellated), corallochytrea (simple free-living saprotrophic organisms that lack flagella), and nucleariids (amoebae with extremely thin pseudopodia).
Although the exact relationships among these protozoa and their relationship with animals and fungi were unclear, it was speculated that the most recent common ancestor (RCA) of animals and fungi was an extinct choanoflagellate-like protozoan (the so-called “choanoflagellate theory”). This was mainly because the morphology of chaonoflagellates resembles that of certain sponge (primitive animals) and chytrid (primitive fungi) cells.
In 2005 researchers resolved the exact relationships among the various opisthokont protozoa and their relationships with animals and with fungi. This work was done in collaboration with researchers at the University of Montreal in Canada and the University of York in the United Kingdom. It involved molecular phylogenetic analyses of large data sets that include multiple gene sequences for many organisms from all of the known eukaryote lineages. Researchers also used information from the complete mitochondrial genomes and EST (sequences for genes that are expressed) genomes that they sequenced.
Research results strongly rejected the choanoflagellate theory. Although most of the examined protozoa are specifically associated with animals, ministeriids appeared to be most closely related to animals. This suggests that the RCA of animals was a ministeriid-like protozoan rather than a choanoflagellate.
Findings also indicate that nucleariids represents the earliest lineage of fungi, which suggests that the RCA of fungi was a nucleariid-like protozoan. This is surprising since fungi share no obvious morphological characters with nucleariids.
Typically, nucleariids are multi- or uninucleate amoebae that feed on algae and bacteria by actively engulfing them, while fungi usually produce networks of apically extending branched multinucleate tubes (hyphae) in which they live and from where they absorb nutrients.
However, this apparent lack of shared derived characters (synapomorphies) may simply be because scientists have not looked for them. A detailed examination of nucleariid traits such as cell-wall chemistry, modes of reproduction, ultrastructure and comparisons with that of fungi, may reveal important characters that will shed light on our understanding of the origin of fungi and the overall evolution of this important group of eukaryotes.
Dr E Steenkamp
Microbiology and Plant Pathology
+27 (0) 12 420 3262
emma.steenkamp@up.ac.za
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