Krokinobacter eikastus

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Higher order taxa

Bacteria>Bacteroidetes>Flavobacteria>Flavobacteriales>Flavobacteriaceae>Krokinobacter>Krokinobacter eikastus



Description and significance

One of five strains of Flavobacteriaceae isolated from marine sediment off the coast of Japan located in the Tokyo and Sagami bays off the Pacific coastline. Krokinobacter eikastus is referred to as type strain PMA-26 T. A surface layer dwelling bacteria, Krokinobacter eikastus plays pivotal roles in the biogeochemical cycle of the euphotic zone in marine environments. In addition, K. eikastus aid in the degradation of organic matter. Scientists have discovered a new functional class of microbial rhodopsin within K. eikastus which functions as a light-driven proton pump known as proteorhodopsins. Krokinobacter was the first discovered light driven sodium pump found within a cell membrane. Light-driven proton pumping rhodopsins are widely distributed among microorganisms establishing proton gradients by converting sunlight to energy the cell can use to drive biological processes. Scientists have discovered a way to manipulate the light-driven transport into a potassium pump. Integrated into neurons this could prove KR2 to be a valuable tool in optogenetics. The surface of the KR2 complex is of particular interest in current research. Research is focused on the primary proteins KR1 and KR2 of the sodium pump. When exposed to light these light-sensitive proteins allowed charged molecules to move into or out of the cell.

Genome structure

The G+C content of DNA is 38%. Sequence accession no. (16S rRNA gene):AB198088. The entire genome has not been fully sequenced in its entirety. Analysis of the 16S rRNA gene sequence divided the five strains into two subgroups with a 2.3% sequence difference.

Cell and colony structure

Cell structure: gram negative, rods, 0.5-0.7 micrometers in width X 2.5-4.0 micrometers in length. Colonies on marine agar are slightly convex, yellow pigmented, 1-2mm in diameter, with both regular and irregular edges. The yellow pigment is due to carotenoids, a class of naturally occurring pigments. K. eikastus can be differentiated from the other four strains by its utilization of mannitol.


Strictly aerobic with an oxidative type of metabolism. Energy acquisition via light-driven Na+ pump. Biolog GN2 microplates in combination with a biolog microstation plate determined the ability of all five strains of Krokinobacter to utilize a total of 95 different carbon sources. 21 of those carbon sources were utilized by all five strains.


K. eikastus is a surface dwelling bacteria with an optimal growth temperature of 20 degrees Celsius and an optimal salt concentration of 3%. K. eikastus has been referred to as the future of optogenetics. Optogenetics is a biological technique that uses light sensitive proteins to control cells in living tissue. Researchers are working specifically with the KR2 protein found within the sodium proton pump and manipulating its structure to find use for it within the field of optogenetics. Current research and development in the field of Optogenetics is focusing on a gene therapy which aims to restore light-sensitivity in the retinas of patients suffering from an inherited disease known as retinitis pigmentosa, which causes retinal degeneration.


Free-living bacteria. The pathology of the species is currently unknown. Particular proteins, specifically KR2 is of current research for application in the field of optogenetics.


Keiichi Inoue, Hikaru Ono, Rei Abe-Yoshizumi, Susumu Yoshizawa, Hiroyasu Ito, Kazuhiro Kogure, Hideki Kandori,“A light-driven sodium ion pump in marine bacteria”,Nature Communications Online Edition: 2013/04/10(Japan time), doi: 10.1038/ncomms2689. Khan, S. T., Nakagawa, Y. & Harayama, S.. Krokinobacter gen. nov., with three novel species, in the family flavobacteriaceae. Int. J. Syst. Evol. Microbiol. 56, 323–328 (2006) . Forschungszentrum Juelich. "Versatile switch for light-controlled cells: The structure of the light-driven ion pump KR2 may provide a blueprint for new optogenetic tools." ScienceDaily. ScienceDaily, 10 April 2015. <>. A light-driven sodium ion pump in marine bacteria Nat Commun 4, 1678, 2013 (2)Khan ST, Nakagawa Y. Harayama S Krokinobacter gen. nov., with three novel species, in the family Flavobacteriaceae Int J Syst Evol Microbiol 56, 323-328, 2006 Ivan Gushchin, Vitaly Shevchenko, Vitaly Polovinkin, Kirill Kovalev, Alexey Alekseev, Ekaterina Round, Valentin Borshchevskiy, Taras Balandin, Alexander Popov, Thomas Gensch, Christoph Fahlke, Christian Bamann, Dieter Willbold, Georg Büldt, Ernst Bamberg& Valentin Gordeliy: Crystal structure of a light-driven sodium pump. Nature Structural & Molecular Biology (2015) doi:10.1038/nsmb.3002

Edited by Kristina Lilley of Dr. Lisa R. Moore, University of Southern Maine, Department of Biological Sciences,