Nostoc flagelliforme

A Microbial Biorealm page on the genus Nostoc flagelliforme

Classification

Higher order taxa

Bacteria; Cyanobacteria; Cyanophyceae; Nostocales; Nostocaceae

Species

NCBI: Taxonomy

Nostoc flagelliforme

Description and significance

Nostoc flagelliforme, one type of blue-green alga, lives in a specific niche with highly varying temperatures, low rainfall, and limited nutrients, but under such conditions it thrives in colonial filaments or alone as single, free-living cells. Its adaptability to its erratic environment is what makes it an intriguing and useful organism. It can be found in arid and semiarid locations within Algeria, China, the former Czechoslovakia, France, Mexico, Mongolia, Morocco, Russia, Somalia, and the United States. In N. flagelliforme’s typical habitat, the changes in temperature from just night to day can be extreme. In Yongden, of the Gansu Province in China, temperatures from night to day differed by 11.0-16.4 degrees Celsius during the summer months. These conditions are important in demonstrating the adaptability of the organism; however; N. flagelliforme’s greatest survival tool may be its ability to desiccate in high temperatures and light exposure for months to even years, and then to recover full photosynthetic activity within hours or days, depending on its surroundings. [2]

It is also important to note that N. flagelliforme is a terrestrial organism. Cultivating in a laboratory environment has proven difficult, if not impossible, for extended periods of time. Aquatic cultures of the organism, such as those used in the lab, may result in altering the chemical and physical properties of the sheath that surrounds its colonies from that grown in the wild. This difference in colonial sheath may be the cause of early disintegration of the sheath and cells by other bacteria. The sheath is presumed to be important for creating a more constant environment around N. flagelliforme colonies, including the capability of retaining water. Disintegration of the sheath as happens in the lab appears to be the cause of colony death. [3]

Genome structure

Unfortunately there is very little genomic data on Nostoc flagelliforme available, but the few proteins that have been documented help to support the more widely distributed claims about the organism. Superoxide dismutase is a protein that has been found in the genome of N. flagelliforme at the locus ABR01632. It is 200 amino acids in length, and it is responsible for catalyzing the conversion of superoxides radicals to hydrogen peroxide and molecular oxygen. The presence of this protein shows us that the organism uses oxygen as a final electron acceptor during respiration. [7]

One other protein found in N. flagelliforme is putative neutral trehalase. This protein is found at the ABO31436 locus and is 469 amino acids long. It serves to aid in the protection of other proteins and membranes against stresses such as heat shock. This protein demonstrates the strong survivability and adaptability of the organism. [8]

Cell structure and metabolism

The primary carbon source of Nostoc flagelliforme is carbon dioxide. Its main metabolic pathway is the conjunction of photosynthesis and dark respiration, but it can also utilize the nitrogen fixation pathway. Due to its terrestrial nature, the organism’s photosynthetic activity is highest when slightly desiccated, or dried. Photosynthesis peaks at 30% water loss, most likely due to a decreased aqueous diffusion barrier for carbon dioxide. Further desiccation results in decreased photosynthetic activity, likely due to loss of intracellular water. Dark respiration is able to increase in productivity until approximately 70% water loss, at which point it lowers to half activity until it stops completely. The further away from the optimal 30% water loss, the less light is required for photosynthesis. It is believed that this is due to inefficient use of high irradiance rather than efficient use of low irradiance. As conditions become less desirable, the cause of a lower light requirement is probably not a change in light source, but photosynthetic efficiency most likely decreases. The organism’s ability to perform tasks such as light harvesting, energy conversion, and carbon assimilation decline as desiccation increases. [2]

N. flagelliforme is known to have a significantly low carbon dioxide compensation point in comparison to other blue-green alga. This means that less carbon dioxide is required for optimal photosynthetic uptake and release. This may be because it possesses a carbon dioxide-concentrating mechanism (CCM) that staggers carbon dioxide use as required. However, it appears that N. flagelliforme’s CCM may be less efficient than that of other organisms. This is important because increased carbon dioxide has been found to augment photosynthetic activity for N. flagelliforme. It is believed that in cultivation attempts, increased carbon dioxide levels will help the bacteria flourish. As carbon dioxide levels increase over time, as is happening across the Earth, it will diminish as a limit for the organism’s growth. Higher temperatures and irradiances will also become less imposing obstacles. (It is important to note that while temperature sensitivity may be present for enzymes involved in photophosphorylation, electron transport, and plastoquinone diffusion, net photosynthetic output varies little within the range of 15-35 degrees Celsius. Such a broad temperature range actually encourages a larger photosynthetic output for the organism, but temperatures in its habitat extend outside of this range.) [2]

After prolonged drought and full desiccation of the organism, its metabolic reactivation goes in order of respiration, photosynthesis, and finally nitrogen fixation. Photosynthetic recovery requires several hours after rehydration. Several factors play a role in recovery time. These factors include the amount of water available for rehydration, and the amount of exogenous potassium ions available. Nutrients like phosphorous play only a minor role in recovery rates. Potassium ions were observed to dramatically increase these rates. Rehydration in a BG11 medium containing adequate K+ resulted in recovery 16 times faster than in distilled water. Peak photosynthetic recovery rates were observed with 345 M K+; however, higher levels of potassium ions have little effect. In the wild, dew may supply the organism with sufficient water while keeping it slightly desiccated, but potassium supplied by rain is limited by evaporation and lack of rain, meaning that N. flagelliforme growth may be limited by K+ levels. K+ is believed to be so important because if its role as a regulatory cation for intracellular pH. It is also a factor in maintaining an ionic environment suitable for preserving the structure of necessary enzymes. [4]

Ecology

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Pathology

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Application to Biotechnology

Does this organism produce any useful compounds or enzymes? What are they and how are they used?

Current Research

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References

[1] Komárek, J., Kling, H. & Komárková, J. "Filamentous Cyanobacteria". Freshwater Algae of North America. (Wehr, J.D. & Sheath, R.G. Eds), pp. 177-196. San Diego: Academic Press.

[2] Qiu, B., and Gao, K. "Photosynthetic characteristics of the terrestrial blue-green alga, Nostoc flagelliforme". European Journal of Phycology. 2001. Volume 36. pp. 147-156.

[3] Gao, K., and Ye, C. "Culture of the terrestrial cyanobacterium, Nostoc flagelliforme (Cyanophyceae), under aquatic conditions". Journal of Phycology. 2003. Volume 39. pp. 617-623.

[4] Qiu, B., and Gao, K. "Dried field populations of Nostoc flagelliforme (Cyanophyceae) require exogenous nutrients for their photosynthetic recovery". Journal of Applied Phycology. 1999. Volume 11. pp. 535-541.

[5] Kanekiyo, K., Hayashi, K., Takenaka, H., Lee, J.B., and Hayashi, T. "Anti-herpes simplex virus target of an acidic polysaccharide, nostoflan, from the edible blue-green alga Nostoc flagelliforme". Biological & Pharmaceutical Bulletin. 2007. Volume 30. pp. 1573-1575.

[6] Yi, Z.W., Huang, H., Kuang, T.Y., and Sui S.F. "Three-dimensional architecture of phycobilisomes from Nostoc flagelliforme revealed by single particle electron microscopy". FEBS Letters. 2005. pp. 3569-73.

[7] Wang, Y., Chen, L.-P., Chen, X., Zhang, X., Yu, J. and Wang, Q.-X. "Cloning and expression of the gene which encodes SOD of Nostoc flagelliforme in E. coli". Unpublished.

Edited by Adam Northrup, student of Rachel Larsen