Gloeomargarita lithophora

Not to be confused with species of Gloeobacter.

Gloeomargarita lithophora, a cyanobacterium, is the proposed closest present day relative of all chloroplasts^[1] (except for the independently evolved in the amoeboid Paulinella chromatophora). The ancient relative of Gloeomargarita's was engulfed by a eukaryotic host in an endosymbiotic event around 1900-1400 million years ago.^[2][3] The origin of plastids by endosymbiosis signifies the beginning of photosynthesis in eukaryotes,^[4] and as such their evolutionary relationship to Gloeomargarita lithophora, as the sister group,^[3] is of high importance to the evolutionary history of endosymbiotic organelles and photosynthesis.

Gloeomargarita lithophora
Image of G. lithophora cells showing carbonate and polyphosphate inclusions taken using annular dark-field imaging (HAADF-STEM).
Scientific classification
Domain:	Bacteria
Phylum:	Cyanobacteria
Order:	Gloeomargaritales
Family:	Gloeomargaritaceae
Genus:	Gloeomargarita
Species:	G. lithophora
Binomial name
Gloeomargarita lithophora

Description

G. lithophora was first isolated in 2007 from microbiolate samples taken from alkaline Lake Alchichica (Mexico). These samples were maintained in a lab aquarium and G. lithophora was isolated from biofilm that occurred within the aquarium. G. lithophora are gram-negative, unicellular rods with oxygenic photoautotrophic metabolism and gliding motility. They contain chlorophyll a and phycocyanin and photosynthetic thylakoids located peripherally. Cells are 1.1 μm wide and 3.9 μm long on average. Growth occurred in both liquid and solid BG-11 growth media, as well as in alkaline water. Optimal growth temperature is 25 °C and optimal growth pH is 8–8.5.^[5]

Bioremediation

Some evidence suggests that Gloeomargarita lithophora could serve as a biological buffer to treat water contaminated with strontium, barium, or radioactive pollutants such as radium. This could be a useful application of bioremediation.^[6][7][8]