Use of a deviant mitochondrial genetic code in yellow-green algae as a landmark for segregating members within the phylum

Abstract

Several algae that were previously classified in the phylum Xanthophyta (yellow-green algae) were assigned in 1971 to a new phylum, Eustigmatophyta. It was anticipated that the number of algae reclassified to Eustigmatophyta would increase. However, due to the fact that the morphological characteristics that segregate eustigmatophytes from other closely related algae can be only obtained through laborious electron microscopic techniques, the number of members in this phylum have increased rather slowly. We attempted, therefore, to segregate two closely related groups of algae, eustigmatophytes and yellow-green algae, on the basis of a molecular phylogenetic tree as a means of providing an alternative method of distinguishing these phyla. We analyzed the mitochondrial cytochrome oxidase subunit I (COXI) gene sequences of eight algae classified as xanthophyceans and found that six manifested the expected deviant genetic code where AUA codes for methionine (AUA/Met), but not for isoleucine (AUA/Ile) as in the universal genetic code. The other two, Monodus sp. (CCMP 505) and Ophiocytium majus (CCAP 855/1), which were presumed to be yellow-green algae, and all the examined eustigmatophytes utilized AUA for Ile. In addition, the phylogenetic tree of COXI gene sequences showed that the six yellow-green algae bearing the AUA/Met deviant code composed a tight clade with a bootstrap value of 100%. The phylogenetic tree of the corresponding sequences from Monodus sp. and Ophiocytium majus and the eustigmatophytes also composed a tight cluster, but with a bootstrap value of 92%. These results strongly suggest that two previously classified members of yellow-green algae belong to the phylum Eustigmatophyta. Therefore, examination of the mitochondrial genetic code in algae appears to be a potentially very useful genetic marker for classifying these organisms, especially when it is considered with the results obtained through a molecular phylogenetic tree.

Genetic variation in bloom-forming ichthyotoxicPseudochattonellaspecies (Dictyochophyceae, Heterokonta) using nuclear, mitochondrial and plastid DNA sequence data

“…In the regions cox1, psbA and rbcL, 11 out of 1723 positions differed when the sequences from P. farcimen were compared with those of P. verruculosa. The usefulness of the mitochondrial and plastid markers (cox1, psbA, rbcL) was in agreement with previous studies of heterokonts (Ehara et al, 1997;Martin & Tooley, 2003;Schena & Cooke, 2006;Evans et al, 2007). Edvardsen et al (2007) showed differentiation between the two Pseudochattonella species by comparing SSU rDNA sequences from two strains: P. farcimen UIO110 and P. verruculosa NIES 670.…”

“…The mitochondrial gene encoding the cytochrome c oxidase subunit 1 (cox1 also referred to as COI) has emerged as the standard identification marker (barcode) for higher animals (Ratnasingham & Hebert, 2007) and marine life (www.coreocean.org). Ehara et al (1997) found cox1 to have appropriate variability to resolve higher order relationships among heterokonts too. Several plastid genes have been used as phylogenetic markers in autotrophic heterokonts (Bachvaroff et al, 2005).…”

The Mechanisms of Codon Reassignments in Mitochondrial Genetic Codes

“…Reassignment of AUA from Ile to Met has also been observed (Ehara et al 1997) in some species of yellow-green algae (Xanthophytes). The entire genome of these species is not yet available and the lack of information about the tRNA genes and codon usage makes it impossible to deduce the mechanism of change.…”

New lipid‐producing, cold‐tolerant yellow‐green alga isolated from the rocky mountains of colorado

“…DN1 appear to be surrounded by an intracellular membrane (Figure ). In other organisms lipid body membranes are composed of a phospholipid monolayer . Lipid bodies in H. sp.…”