Galdieria

Galdieria is a genus of red algae belonging to the order Galdieriales;^[1] family Galdieriaceae.^[2] It was created by Italian botanist Aldo Merola in 1981 for the identification from the species of Cyanidium.^[3][4]

Galdieria
Scientific classification
Domain:	Eukaryota
Clade:	Archaeplastida
Division:	Rhodophyta
Class:	Cyanidiophyceae
Order:	Cyanidiales
Family:	Galdieriaceae
Genus:	Galdieria Merola et al., 1981

Species:^[2]

• Galdieria daedala O.Yu.Sentsova, 1991
• Galdieria maxima O.Yu.Sentsova, 1991
• Galdieria partita O.Yu.Sentsova, 1991
• Galdieria phlegrea Pinto et al., 2007
• Galdieria sulphuraria (Galdieri) Merola et al., 1981
• Galdieria javensis H.S.Yoon et al., 2023
• Galdieria yellowstonesis H.S.Yoon et al., 2023

There are around 7 species in Galdieria, with cryptic species in the species complex G. sulphuraria. The species in Galdieria are extremophilic and mixotrophic, using more than 50 external carbon source for metablism.^[5]

Recently, researchers have induced haploid cell generation and sexual reproduction in G. sulphuraria(NIES-550) , G. yellowstonesis(SAG108.79) and G. partita(NBRC102759) under the condition of pH=1.0.^[6] Both diploid and haploid cells are mixotrophic, the main difference between them being the cell wall; only diploid cells have cell wall. There are two haploid cells types. One is the common round cell, while the other is the 'tadpole-shaped' cell. The latter is motile, but the tail is not a cilium. They also found two kind of haploid cell while isogamy mating, and turning out the heterozygous individuals. The other is self-diploidization by haploid endoreduplication under the acetic acid stress, and turning out the homozygous individuals. The previous observation of life cycle in Galdieria was regarded as asexual reproduction, although some molecular evidence showed at least 4 time recombinations in last recent (??).^[7] This study is the first observation of sexual reproduction, it might reveal more clues about the ecological function of this lineage. For examples, the diploid cells in Galdieria can tolerate a wider range of pH, but the haploid cell might dominate in habitats with lower pH.

This lineage mainly thrives in the sulphur acidic geothermal area (30–60°C, pH=0.0–4.0), one of reasons making them tolerant such extreme environment might because the horizontal gene transfer (HGT) for prokaryotes. In the pangenome of Galdieria, showing around 5% genes gained from HGT, and 1% of genes drove them survive from heavy metals, cold stress, and other harsh conditions.^[8]

The specific physiological and ecological function make Galdieria become a suitable material for eukaryotes to investigate the adaptation and evolution on the early earth.^[9]

The other aspect of application in this lineage is to deal with the water pollution,^[10] cause the mixotrophic feature and high tolerance to the heavy metal, Galdieria can serve as a efficient material for the water pollution.

Although the morphological traits are hard to use for classification and still some cryptic species existing. Overall, this genus was highly development in molecular analysis, 15 genome of different strains had been publicated on NCBI^[11] at least.