Arthrospira maxima
Classification
Bacteria, Cyanobacteria, Oscillatoriales, Arthrospira, A. maxima
Cell Description
Arthrospira maxima is an aquatic blue green alga, where cells are joined from end to end to form twisted filaments. It is an oxygenic phototroph, which means that it uses sunlight and water to acquire its energy. It is a colonial filamentous bacteria that survives in high concentrations of sodium and high pH. It comprises one of the most efficient in vivo water oxidizing complexes, which is accompanied by a high quantum efficiency in photosystem 2. The filaments have no heterocysts, meaning they are unable to fix and use nitrogen as a source of energy. It is usually a pale or bright blue green color and its thylakoids sit irregularly and perpendicularly along the cell wall. It will reproduce by fragmenting the trichromes into motile portions of filament. They separate out and then develop by normal cell division and will not divide again until a normal size is obtained.
Metabolism
The main metabolic pathway is photosynthesis, however fermentation also plays a major role for the life of Arthrospira maxima. Anaerobic hydrogen production is catalyzed by a bidirectional nickel/iron hydrogenase and is linked to the light dependant production of NADPH and the dark production of NADH. The break-down of these compounds is a major pathway for energy production by regenerating NAD and NADP. High levels of Ni, during photoautotrophic growth, cause stress and will cause chlorophyll breakdown and slow growth rate of the bacteria. If large amounts of nitrate are present hydrogen production will be slowed because nitrate is a competing substrate for consumption of NADPH.
Genome Structure
Arthrospira maxima has a genome size of 5.4 Mb or 5,400,000 base pairs. The entire genome has been sequenced and is available through the Departments of Energy’s Joint Genome Institute in raw form. Only a portion of the entire genome has been analyzed. Genes that were involved in DNA replication, repair, modification, transcription and translation were identified. Most of the genes sequenced were involved with DNA replication and repair. Many genes that were involved in energy metabolism were identified. Some important sequences encoding gas vacuole proteins, so the bacteria can remain in the photic zone, were identified. Photosystem encoding genes were identified as well. Genes that encoded proteins for nutrient transport and circadian rhythms were also identified. There were 252 genes, that likely coded for protein, whose function could not be readily identified. It is possible that these gene sequences are unique to Arthrospira maxima.
Ecology
Arthrospira maxima are found in tropical and subtropical regions where there are warm bodies of water with high ph, carbonate, and salinity levels. It is common in soda lakes of the Rift Valley, in Africa, and Mexico. The organism has been collected and used as food for hundreds of years. It is consumed because of its high protein and nutrient content. The annual production of Arthrospira maxima and close relatives is estimated to be 3,000 tons. Arthrospira maxima can tolerate high levels of bicarbonate, carbonate, salinity and pH. It has been observed in water with a pH as high as 11. The species can reach very high cell densities. In a laboratory culture the density has been recorded at 3g dry weight per liter. In Africa, A. maxima serve as a food source for filter feeding flamingoes in soda lakes. The carotenoids in A. maxima give the birds their pink color.
Current Research
The use of cyanobacteria to produce hydrogen and oxygen from solar radiation is a promising, new technology for the production non-fossil fuel based energy. Biologically produced fuel is gaining popularity as fossil fuels are becoming more expensive and scarce. Arthrospira maxima ferments carbon compounds in the absence of light to produce hydrogen. This process is carried out in part by the hydrogenase enzyme which requires iron and nickel to operate. The rate of hydrogen production can be increased by raising the Nickel concentration. A. maxima’s is very promising because it is easy to culture, can achieve high cell densities and can produce hydrogen efficiently.
References
Ananyev G., D. Carrieri, G. C. Dismukes. 2008. Optimization of Metabolic Capacity and Flux through Environmental Cues To Maximize Hydrogen Production by the Cyanobacterium “Arthrospira (Spirulina) maxima”. APPLIED AND ENVIRONMENTAL MICROBIOLOGY 74:19 p. 6102–6113
Arthrospira maxima CS-328. April 2009. Joint Genome Instutite; US Department of Energy. <genome.jgi-psf.org/draft_microbes/artma/artma.info.html>
Carrieria D., G. Ananyeva, A. M. Garcia Costasb, D. A. Bryantb, G. C. Dismukes. 2008. Renewable hydrogen production by cyanobacteria: Nickel requirements for optimal hydrogenase activity. INTERNATIONAL JOURNAL OF HYDROGEN ENERGY 33:2014 – 2022.
Ling N., Y. Mao, X. Zhang, Z. Mo, G. Wang, W. Liu. 2007. Sequence analysis of Arthrospira maxima based on fosmid library. Journal of Appl Phycol 19:333–346
Mühling M., P. J. Somerfield, N. Harris, A. Belay, B. A. Whitton. 2006. Phenotypic analysis of Arthrospira (Spirulina) strains (cyanobacteria). Phycologia 45: 2, 148-157.
Kruse O., J. Rupprecht, J. H. Mussgnug, G. C. Dismuke, B. Hankamer. 2005. Photosynthesis: a blueprint for solar energy capture and biohydrogen production technologies. Photochem Photobiol Sci 4: 957–969
Vincent K. A., J.A. Cracknell, A. Parkin and F.A. Armstrong. 2005 .Hydrogen cycling by enzymes: electrocatalysis and implications for future energy technology. Dalton Transactions (21), 3397-3403.
