Published descriptions of thermoacidophilic unicellular algae date to the mid-19th century. The earliest description of an organism corresponding to the modern G. sulphuraria was published in 1899 by an Italian scientist, A. Galdieri, who gave it the name Pleurococcus sulphurarius. The
taxonomy of thermoacidophilic algae was revised in 1981, which introduced the
genusGaldieria and gave the organism its modern designation.[1][4]G. sulphuraria is the
type species for this genus.[1][2]
The group to which G. sulphuraria belongs, the
Cyanidiophyceae, is the most deeply branching subgroup of the
rhodophyta (red algae), meaning they were the earliest to diverge in the
evolutionary history of this group.[5]
Metabolism
G. sulphuraria is noted for its extreme
metabolic flexibility: it is capable of
photosynthesis and can also grow
heterotrophically on a wide variety of carbon sources, including diverse
carbohydrates. Over 50 different carbon sources that support growth have been reported.[6][7][8] Careful measurements of its growth patterns under laboratory conditions suggest that it is not a true
mixotroph capable of using both energy sources at the same time; rather, it prefers heterotrophic growth conditions and downregulates photosynthesis after extended exposure to extracellular carbon sources.[9] Analysis of the G. sulphurariaphotosystem I complex, a key photosynthetic component, suggests a structure intermediate between the homologous complexes in
cyanobacteria and
plants.[8]
Although most red algae use
floridean starch as a storage
glucan, G. sulphuraria uses a highly unusual form of
glycogen which is among the most highly branched glycogens known, has very short branch lengths, and forms particles of unusually low
molecular weight. These properties are believed to be metabolic adaptations to extreme environmental conditions, although the precise mechanism is unclear.[10]
Habitat and ecology
G. sulphuraria is unusual for a
eukaryote in being
thermoacidophilic – that is, capable of growing at both high temperature and low
pH. It grows well in a pH range of 0–4 and at temperatures up to 56 °C,[9] close to the approximately 60 °C sometimes cited as the likely maximum for eukaryotic life.[11][12] It is also highly tolerant of high
salt concentrations and of toxic metals. It is found in naturally acidic
hot springs, in
solfataric environments, and in polluted environments;[3] It is also found in
endolithic ecosystems, where light is scarce and its heterotrophic metabolic capacities are particularly important.[13][14][15] Laboratory tests indicate that it is capable of actively acidifying its environment.[9]
Genome
The G. sulphurariagenome contains evidence of extensive
horizontal gene transfer (HGT) from thermoacidophilic
archaea and
bacteria, explaining the origin of its
adaptation to this environment. At least 5% of its
proteome is likely to be derived from HGT.[3] This is highly unusual for a eukaryote; relatively few well-substantiated examples exist of HGT from prokaryotes to eukaryotes.[16]
The genome of its
mitochondria is also exceptionally small and has a very high
GC skew, while the genome of its
plastids is of normal size but contains an unusual number of
stem-loop structures. Both of these properties are proposed to be adaptations for the organism's polyextremophilic environment.[17] By comparison to Cyanidioschyzon merolae – a unicellular thermoacidophilic red alga that is obligately photoautotrophic – the G. sulphuraria genome contains a large number of genes associated with carbohydrate metabolism and cross-membrane transport.[18]
Biotechnology
Because of its ability to tolerate extreme environments and grow under a wide variety of conditions, G. sulphuraria has been considered for use in
bioremediation projects. For example, it has been tested for the ability to recover
precious metals,[19] recover
rare-earth metals,[20] and remove
phosphorus and
nitrogen[21] from various waste streams.
It is also an interesting source of proteins and especially phycocianin. The phycocianin produced by this specie is interesting since it is thermoresistant and acidotestant, two interesting properties for food application.
References
^
abcMerola, Aldo; Castaldo, Rosa; Luca, Paolo De; Gambardella, Raffaele; Musacchio, Aldo; Taddei, Roberto (1981). "Revision of Cyanidium caldarium. Three species of acidophilic algae". Giornale Botanico Italiano. 115 (4–5): 189–195.
doi:
10.1080/11263508109428026.
^
abGuiry, M.D.; Guiry, G.M.
"Galdieria sulphuraria". AlgaeBase. World-wide electronic publication, National University of Ireland, Galway.
^Yoon, Hwan Su; Muller, Kirsten M.; Sheath, Robert G.; Ott, Franklyn D.; Bhattacharya, Debashish (April 2006). "Defining the Major Lineages of Red Algae (Rhodophyta)1". Journal of Phycology. 42 (2): 482–492.
doi:
10.1111/j.1529-8817.2006.00210.x.
S2CID27377549.
^Weber, AP; Horst, RJ; Barbier, GG; Oesterhelt, C (2007). "Metabolism and metabolomics of eukaryotes living under extreme conditions". International Review of Cytology. 256: 1–34.
doi:
10.1016/S0074-7696(07)56001-8.
ISBN9780123737007.
PMID17241903.