Friday, January 02, 2015

Joint PNNL/Penn State study addresses photoacclimation in Synechococcus PCC 7002

Alexander S. Beliaev of PNNL and Donald A. Bryant of Penn State have an interesting paper in "Frontiers in Microbiology" titled "Effect of mono- and dichromatic light quality on growth rates and photosynthetic performance of Synechococcus sp. PCC 7002."

They employed turbidostatic cultivation to the study effects of varying 630- and 680-nm light intensities upon steady-state growth of Synechococcus PCC 7002. They noted that rapid specific growth rates (μ) of up to 0.2 h−1 (doubling time of 3.5 h) were achieved when Synechococcus 7002 was cultivated in turbidostat mode under light-limited conditions at 30°C. The conditions were such that --Cell densities of 0.09 (OD730), corresponding to 34 ± 4 mgAFDWL−1, were constantly maintained to reduce self-shading in the photobioreactor. -- Turbidostatic cultivation provides a means to investigate steady states defined by the maximum growth rate of an organism at a given condition, without altering the cell culture density of the culture. In the context of phototrophic growth, turbidostats enable the maintenance of optically thin (i.e., low OD) cultures.

Among other things, the authors observed:

Notably, under monochromatic light conditions, cultures exhibited similar growth rates only when they were irradiated with 630 nm light; cultures irradiated with only 680 nm light grew at rates that were 60–70% of those under other light quality regimes at equivalent irradiances.

The authors concluded

We infer that these results reflect the plasticity of the photosynthetic apparatus to photoacclimate via a series of mechanisms including modulation of phycobilisome and reaction center size and stoichiometry, as well as the ability to redistribute excitation energy efficiently and effectively between the two photosystems.


Beliaev is co-inventor on published US patent application 20130149766 , titled PRODUCTION OF BIO-BASED MATERIALS USING PHOTOBIOREACTORS WITH BINARY CULTURES.

Bryant is co-inventor on published US patent application 20130171677 , titled RECOMBINANT PHYCOBILIPROTEINS WITH ENHANCED FLUORESCENCE AND PHOTOCHEMICAL PROPERTIES, which includes the text

The phycobiliproteins are a family of light-harvesting proteins found in cyanobacteria, red algae, and the cryptomonads. These proteins absorb strongly in the visible region of the spectrum because they carry various covalently attached linear tetrapyrrole prosthetic groups (bilins). Their ability to absorb and conduct light energy to chlorophylls is due to the posttranslational covalent attachment of linear tetrapyrrole chromophore(s) to cysteine residue(s) in the chromophore binding pockets(s) of these proteins. The highly efficient transfer of energy to chlorophylls of the photosystems in the natural system causes them to have nearly no fluorescence when properly assembled in vivo, but when phycobilisomes are purified from cells, they are highly fluorescent due to the absorption of light energy and the inability to transfer that energy to downstream chlorophyll acceptors.


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