Comparative ultrastructural analysis of Chloromonas and Gloeomonas (Chlorophyceae): tracing the origin of Gloeomonas-specific basal apparatus traits

Abstract: On the basis of prior phylogenetic analyses placing Gloeomonas as a lineage within the very diverse genus Chloromonas, it was hypothesized that the morphologically distinct Gloeomonas, bearing widely spaced basal bodies, evolved from ancestral organisms like Chloromonas. In addition, the phylogenetically related Chloromonas (Cr.) rubrifilum, was expected to possess traits intermediate to the two forms. To test these hypotheses, we performed detailed transmission electron microscope analysis on nine species of these genera. The species were divided into two categories on the basis of ultrastructural features: group 1, consisting of four diverse species of Chloromonas and Ixipapillifera, had a V-shaped basal body arrangement, and group 2, of Cr. rubrifilum and four Gloeomonas species, forming a single clade possessing widely spaced basal bodies. Members of group 1 commonly had a simple, flat plate-like distal connecting fiber (dcf), three or sometimes two microtubules in the sinister root, continu...