''Gloeobacter'' is a genus of

cyanobacteria Cyanobacteria (), also known as Cyanophyta, are a phylum of gram-negative bacteria that obtain energy via photosynthesis. The name ''cyanobacteria'' refers to their color (), which similarly forms the basis of cyanobacteria's common name, bl ...

. It is the

sister group In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and ...

to all other

. ''Gloeobacter'' is unique among cyanobacteria in not having

thylakoid Thylakoids are membrane-bound compartments inside chloroplasts and cyanobacteria. They are the site of the light-dependent reactions of photosynthesis. Thylakoids consist of a thylakoid membrane surrounding a thylakoid lumen. Chloroplast thyl ...

s, which are characteristic for all other cyanobacteria and

chloroplast A chloroplast () is a type of membrane-bound organelle known as a plastid that conducts photosynthesis mostly in plant and algal cells. The photosynthetic pigment chlorophyll captures the energy from sunlight, converts it, and stores it i ...

s. Instead, the light-harvesting complexes (also called

phycobilisome Phycobilisomes are light harvesting antennae of photosystem II in cyanobacteria, red algae and glaucophytes. It was lost in the plastids of green algae / plants (chloroplasts). General structure Phycobilisomes are protein complexes (up to 6 ...

s), that consist of different proteins, sit on the inside of the

plasma membrane The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of all cells from the outside environment (t ...

among the (

cytoplasm In cell biology, the cytoplasm is all of the material within a eukaryotic cell, enclosed by the cell membrane, except for the cell nucleus. The material inside the nucleus and contained within the nuclear membrane is termed the nucleoplasm. ...

). Subsequently, the

proton gradient An electrochemical gradient is a gradient of electrochemical potential, usually for an ion that can move across a membrane. The gradient consists of two parts, the chemical gradient, or difference in solute concentration across a membrane, and ...

in ''Gloeobacter'' is created over the plasma membrane, where it forms over the thylakoid membrane in cyanobacteria and chloroplasts. The whole genome of ''G. violaceus'' (strain PCC 7421) and of ''G. kilaueensis'' have been sequenced. Many genes for

photosystem Photosystems are functional and structural units of protein complexes involved in photosynthesis. Together they carry out the primary photochemistry of photosynthesis: the absorption of light and the transfer of energy and electrons. Photosy ...

I and II were found missing, likely related to the fact that

photosynthesis Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored in ...

in these bacteria does not take place in the thylakoid membrane as in other cyanobacteria, but in the

Description

''Gloeobacter violaceus'' produces several pigments, including chlorophyll a, β-carotene, oscillol diglycoside, and

echinenone Echinenone is a xanthophyll, with formula C40H54O. It is found in some cyanobacteria. It is synthesized from β-carotene by the enzyme beta-carotene ketolase (or CrtW). It has also been isolated from sea urchins Sea urchins () are spiny, g ...

. The purple coloration is due to the relatively low chlorophyll content. ''G. kilaueensis'' grows with a few other bacteria as a purple-colored

biofilm A biofilm comprises any syntrophic consortium of microorganisms in which cells stick to each other and often also to a surface. These adherent cells become embedded within a slimy extracellular matrix that is composed of extracellular po ...

around 0.5 mm thick. Cultivated colonies are dark purple, smooth, shiny, and raised. ''G. kilaueensis'' is mostly unicellular, capsule-shaped, about 3.5×1.5 µm, and imbedded in mucus. They divide over the width of the cell. Cells color gramnegative, and lack

vancomycin Vancomycin is a glycopeptide antibiotic medication used to treat a number of bacterial infections. It is recommended intravenously as a treatment for complicated skin infections, bloodstream infections, endocarditis, bone and joint infection ...

resistance. They are not

motile Motility is the ability of an organism to move independently, using metabolic energy. Definitions Motility, the ability of an organism to move independently, using metabolic energy, can be contrasted with sessility, the state of organisms th ...

and do not glide. Growth ceases in complete darkness, so ''Gloeobacter'' is very likely obligatory photoautotrophic.

Species and distribution

''Gloeobacter violaceus'' was found on a limestone rock in the Swiss canton

Obwalden Obwalden, also Obwald (german: Kanton Obwalden, rm, Chantun Sursilvania; french: Canton d'Obwald; it, Canton Obvaldo), is one of the 26 cantons forming the Swiss Confederation. It is composed of seven municipalities and the seat of the gover ...

. ''G. kilaueensis'' occurred within a lava cave at the Kilauea-caldera on Hawaii. It grew there at a temperature around 30 °C at very high humidity, with moisture condensing and dripping off the biofilm. ''Gloeobacter'' could have split off from the other cyanobacteria between 3.7 and 3.2 billion years ago. The species of ''Gloeobacter'' may have branched 280 million years ago. ''Anthocerotibacter panamensis'', found in a sample of

hornwort Hornworts are a group of non-vascular Embryophytes (land plants) constituting the division Anthocerotophyta (). The common name refers to the elongated horn-like structure, which is the sporophyte. As in mosses and liverworts, hornworts have a ...

from a rainforest in Panama, also lacks thylakoids. It has very few of the genes that are required to perform photosynthesis, but is still able to perform it, very slowly. It may have been split from ''Gloeobacter'' about 1.4 Ga ago. According to AlgaeBase this genus is also a member of the family Gloeobacteraceae.AlgaeBase
''Anthocerotibacter'' F.-W.Li, 2021
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References

{{Taxonbar, from=Q5571156 Cyanobacteria genera Cyanobacteria