Sexual reproduction of the snow alga Chloromonas fukushimae (Volvocales, Chlorophyceae) induced using cultured materials

Abstract

Snow algae are microalgae, growing in melting snowpacks, and are thought to act as primary producers in the snow ecosystem. Chloromonas (Volvocales, Chlorophyceae) contains more than 15 snow-inhabiting species. Although vegetative cells and zygotes, or asexual cysts, of snow species of the genus are frequently collected in the field, sexual reproduction and zygote formation in culture have only been induced in C . tughillensis . Here we describe the sexual reproduction of another snow-inhabiting species, C . fukushimae , which was induced using both previously examined and newly established Japanese strains. Mating of isogamous gametes began after mixing two different strains, implying that C . fukushimae is an outcrossing species. Motile and nonmotile zygotes of the species were also described in this report. The nonmotile zygote of C . fukushimae was distinguishable from those of the other snow-inhabiting species of Chloromonas , based on the zygote shape and the presence of several large lipid bodies within the cell. In addition, C . fukushimae carried out sexual reproduction and produced zygotes even under the nitrogen-sufficient condition.

Cysts of the Snow Alga Chloromonas krienitzii (Chlorophyceae) Show Increased Tolerance to Ultraviolet Radiation and Elevated Visible Light

“…The flagellates of C. krienitzii were "backward"-swimmers, meaning that during the cell movement the flagella are in the rear (Supplementary Video 1). In this study, sexual reproduction (e.g., Matsuzaki et al, 2020) was not observed.…”

The snow alga Chloromonas kaweckae sp. nov. (Volvocales, Chlorophyta) causes green surface blooms in the high tatras (Slovakia) and tolerates high irradiance

“…Aggregates of 16 or more cells resulting in the repeated division of daughter cells within the parental cell wall (e.g., Matsuzaki et al 2018) were not produced even in 2-month-old cultures. Sexual reproduction and production of cysts or zygotes were not observed in the culture, even when using the induction method for Chloromonas fukushimae and C. tughillensis (Matsuzaki et al 2020). Cells of C. kaweckae showed no growth at 15°C after cultivation for 2 weeks, as described in previous reports of other snow-inhabiting Chloromonas species (e.g., Matsuzaki et al 2019), this may suggest that it represents a psychrophile (i.e., coldloving organism with growth temperature optima below 15°C).…”

“…Sexual reproduction and production of cysts or zygotes were not observed in the culture, even when using the induction method for Chloromonas fukushimae and C. tughillensis (Matsuzaki et al. 2020 ). Cells of C .…”

“…They evolved complex life cycles which enabled them to colonize melting snow (Hoham and Duval 2001 , Matsuzaki et al. 2020 ). At exposed sites, the apparently high‐light sensitive green flagellate stages are usually found in deeper parts of the snowpack under milder light conditions, while later in the season, when the cells are exposed on the snow surface, they already have entered robust and orange to reddish pigmented cyst stages that are less susceptible to damage from high irradiance and other stresses (Sattler et al.…”

Rosetta gen. nov. (Chlorophyta): Resolving the identity of red snow algal rosettes

“…But of the genus Rosetta , no member of which has yet been cultured, there is little that can be said definitively about life histories. Those Chloromonadinia species that have been successfully cultivated and induced to undergo sexual reproduction exhibit a lifecycle reminiscent of the model organism Chlamydomonas reinhardtii , which produce thick‐walled brownish‐orange zygotes (Hoham, 1975; Hoham et al., 1983; Matsuzaki et al., 2020; Procházková et al., 2020). Field observations have tempted some researchers to map this life history onto the ruby‐like cells of Rosetta and Sanguina ; however, given the diversity of species present in field samples, these conclusions are not definitive.…”