Biomedical Engineering Reference
In-Depth Information
of fungi, which accommodates the ascomyceteous yeasts. Within this branch, recog-
nized by the current classification in the phylum Ascomycota, as the subphylum
Saccharomycotina, class Saccharomycetes, order Saccharomycetales [
2
] , sourdough
yeasts belong to different genera. The major sourdough yeasts belong to genera that
are currently placed in the family Saccharomycetaceae, although family assignment of
yeast genera is still difficult because of a lack of informative data. Basidiomycetous
yeasts and dimorphic ascomycetes, also adapted to growth in liquid environments by
unicellular growth forms, lack the fermentative abilities that are common to the
Saccharomycetales and that are important for growth under oxygen limitations. The
taxonomy of the Saccharomycetales, classically based on morphology and physiol-
ogy, is in the process of being adapted to the increasing knowledge of evolutionary
relationships reconstructed from gene sequences, in other words, a phylogenetic sys-
tem of classification is being developed [
2
]. This implies a number of name changes.
The new genus names have the advantage of reflecting the common genetic back-
ground of related yeast species, hereby providing an informative classification in
contrast to the former largely artificial classification.
An overview of recent name changes restricted to species that have been obtained
from sourdough is given here. The name changes most relevant to the yeasts found
in sourdough concern the genera
Saccharomyces
Meyen ex Reess and
Pichia
E.C.
Hansen emend. Kurtzman. The genus
Saccharomyces
has been limited to the group
of species known as
Saccharomyces sensu stricto
, including the type species of the
genus,
Saccharomyces cerevisiae,
on the basis of multiple gene sequences [
3
] . The
group of species formerly often addressed as
Saccharomyces sensu lato
has been
divided into several genera. The new genus
Kazachstania
is accommodating the
former
Saccharomyces exiguus
,
Saccharomyces unisporus,
and
Saccharomyces
barnettii
as
Kazachstania exigua
,
Kazachstania unispora
, and
Kazachstania bar-
nettii
, respectively.
Saccharomyces kluyveri
has been assigned to the new genus
Lachancea
as
Lachancea kluyveri
. The genus
Pichia
has been restricted to species
closely related to the generic type species
Pichia membranifaciens
, including
Pichia
fermentans
[
4
] . The former genus
Issatchenkia
has been integrated into the newly
de fi ned genus
Pichia
as its species are located on the same branch as the type spe-
cies
P. membranifaciens
on the phylogenetic tree based on multiple gene sequences
used for the redefinition of genera. While the species epithet of
Issatchenkia occi-
dentalis
has been preserved in its new name
Pichia occidentalis
, a complete name
change of
Issatchenkia orientalis
to
Pichia kudriavzevii
was necessary as the com-
bination
Pichia orientalis
had been used for a different species before. The former
species
Pichia anomala
and
Pichia subpelliculosa
were found to be only distantly
related to the generic type species
P. membranifaciens
and have therefore been
assigned to the newly created genus
Wickerhamomyces
as
Wickerhamomyces anom-
alus
and
Wickerhamomyces subpelliculosus
. A review of the taxonomic consider-
ations including the earlier genus name
Hansenula
has been given by Kurtzman
[
5
,
6
]. Other, only occasionally from sourdough isolated species from the former
genus
Pichia
have been reassigned to new genera, while preserving their species
epithet and include
Kodamaea ohmeri, Meyerozyma guilliermondii
,
Millerozyma
farinosa
,
Ogataea polymorpha
,
Saturnispora saitoi,
and
Scheffersomyces stipitis
.
