Analyses of hyphal diversity in Trichosporonales yeasts based on fluorescent microscopic observations
Authors: Aoki Keita , Ohkuma Moriya , Sugita Takashi , Kobayashi Yuuki , Tanaka Naoto , Takashima Masako 
Published: February 2025

In dimorphic yeasts, hyphal growth is primarily associated with infection and mycosis progression, with
Trichosporon asahii
causing deep-seated mycosis and summer-type hypersensitivity pneumonitis. Magnesium accelerates hyphal growth in
T. asahii
, leading to multi-septation, vacuolar expansion, and decreased lipid droplet size. However, the commonality of these phenotypes has not been studied in Trichosporonales yeasts. Therefore, to explore whether similar magnesium-induced phenotypes occur across Trichosporonales yeasts, we examined hyphal growth, multi-septation, vacuolar extension, and lipid droplet size and number in 30 species. Cell length increased with magnesium treatment in 13 yeasts: 5
Trichosporon
(
T. asahii
,
Trichosporon aquatile
,
Trichosporon asteroides
,
Trichosporon coremiiforme
, and
Trichosporon ovoides
), three
Apiotrichum
(
Apiotrichum brassicae
,
Apiotrichum montevideense
, and
Apiotrichum veenhuisii
), three
Cutaneotrichosporon
(
Cutaneotrichosporon cavernicola
,
Cutaneotrichosporon cutaneum
, and
Cutaneotrichosporon dermatis
),
Pascua guehoae
, and
Takashimella koratensis. C. dermatis
also underwent pseudo-hyphal growth. Multi-septation increased in seven dimorphic yeasts, including five
Trichosporon
spp.,
Trichosporon faecale
, and
C. dermatis
. The vacuolar area was significantly extended in
T. asahii
,
T. aquatile
,
T. ovoides
, and
C. dermatis
. Lipid droplet size increased only in
Trichosporon inkin
; however, it decreased in
T. asahii
,
T. coremiiforme
, and
T. faecale
. Additionally, lipid droplet number was preferentially altered in
Apiotrichum
and
Cutaneotrichosporon
. These results suggested that magnesium-induced multi-septation and vacuolar area expansion phenotypically distinguish
Trichosporon
hyphae from
Apiotrichum
and
Cutaneotrichosporon
hyphae and distinguish
C. dermatis
pseudo-hyphae from
Cutaneotrichosporon
spp. Moreover, differences in lipid droplet size can discriminate species within
Trichosporon
. Our results suggest that phenotypic alteration via magnesium treatment can contribute to the characterization of Trichosporonales yeasts. These findings provide insights into fungal pathogenesis and may support new treatment strategies.

IMPORTANCE

Magnesium sulfate considerably affects hyphal growth and cellular organization in
Trichosporon asahii
. To examine the commonality of this phenotype in Trichosporonales, we treated 30 Trichosporonales yeasts with magnesium sulfate and observed genus-level phenotypic alterations. Using cell length measurement, lipid droplet staining, septum staining, and vacuole staining, considerable hyphal diversity was observed among Trichosporonales. Notably, differences in the multi-septation phenotype and vacuolar size distinguished
Trichosporon
hyphae from
Apiotrichum
and
Cutaneotrichosporon
hyphae and distinguished
Cutaneotrichosporon dermatis
from other
Cutaneotrichosporon
spp. Moreover, differences in lipid droplet phenotype divided
Trichosporon
hyphae into two groups. Our study revealed the relationship between hyphal morphology and phylogenetic systematics in Trichosporonales.