Horizontal gene transfer promoted the evolution of the ability to propagate under anaerobic conditions

In English The ability to propagate under anaerobic conditions
is an essential and unique trait of brewer’s or
baker’s yeast (Saccharomyces cervisiae). To understand
the evolution of facultative anaerobiosis we studied the
dependence of de novo pyrimidine biosynthesis, more
precisely the fourth enzymic activity catalysed by dihydroorotate
dehydrogenase (DHODase), on the enzymes
of the respiratory chain in several yeast species. While
the majority of yeasts possess a mitochondrial DHODase,
Saccharomyces cerevisiae has a cytoplasmatic enzyme,
whose activity is independent of the presence of
oxygen. From the phylogenetic point of view, this enzyme
is closely related to a bacterial DHODase from
Lactococcus lactis. Here we show that S. kluyveri, which
separated from the S. cerevisiae lineage more than 100
million years ago, represents an evolutionary intermediate,
having both cytoplasmic and mitochondrial
DHODases. We show that these two S. kluyveri enzymes,
and their coding genes, differ in their dependence
on the presence of oxygen. Only the cytoplasmic
DHODase promotes growth in the absence of oxygen.
Apparently a Saccharomyces yeast progenitor which had
a eukaryotic-like mitochondrial DHODase acquired a
bacterial gene for DHODase, which subsequently
allowed cell growth gradually to become independent of
oxygen.