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Abstract
Culturing cyanobacteria in a highly alkaline environment is a possible strategy for controlling contamination by other organisms. Synechocystis PCC 6803 cells were grown in continuous cultures to assess their growth performance at different pH values. Light conversion efficiency linearly decreased with the increase in pH and ranged between 12.5 % (PAR) at pH 7.5 (optimal) and decreased to 8.9 % at pH 11.0. Photosynthetic activity, assessed by measuring both chlorophyll fluorescence and photosynthesis rate, was not much affected going from pH 7.5 to 11.0, while productivity, growth yield, and biomass yield on light energy declined by 32, 28, and 26 % respectively at pH 11.0. Biochemical composition of the biomass did not change much within pH 7 and 10, while when grown at pH 11.0, carbohydrate content increased by 33 % while lipid content decreased by about the same amount. Protein content remained almost constant (average 65.8 % of dry weight). Cultures maintained at pH above 11.0 could grow free of contaminants (protozoa and other competing microalgae belonging to the species of Poterioochromonas).Electronic supplementary materialThe online version of this article (doi:10.1007/s00253-015-7024-0) contains supplementary material, which is available to authorized users.
Highlights
The cyanobacterium Synechocystis PCC 6803 is being widely used as a model organism for the study of photosynthetic processes, since it is well characterized and can be transformed
Non-photochemical quenching (NPQ) values of chlorophyll fluorescence were found to be very low, and qP was consistently at relatively high values between 0.85 and 0.90 in the range of pH 7.5–10.5, which indicates that most of the absorbed energy was used for photochemistry (Table 2)
We found that outdoor cultures of Synechocystis, grown in a closed photobioreactor, were systematically subjected to severe contamination by Poterioochromonas sp
Summary
The cyanobacterium Synechocystis PCC 6803 is being widely used as a model organism for the study of photosynthetic processes, since it is well characterized and can be transformed. The use of Synechocystis PCC 6803 (hereafter Synechocystis) has been proposed for the production of biohydrogen as well as chemicals and biomaterials (Gao et al 2012; Sharma et al 2011; Yu et al 2013; Englund et al 2014) It has been genetically engineered for the photosynthetic production of isoprene, a hydrocarbon currently used as feedstock in the synthetic chemistry industry for the production of commercial commodities (Chaves et al 2015). A number of recent reports have indicated that cultures in closed systems are often affected by contaminants in spite of their protection from the outside atmosphere (Rego et al 2015; Hoffman et al 2008; Forehead and O’Kelly 2013; Carney and Lane 2014; Zemke et al 2013). It has been found that in many cases, the main vehicle of the contamination is represented by the water used for preparing the medium
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