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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.

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The UV-A (320-400 nm) component of sunlight is a significant damaging factor of plant photosynthesis, which targets the photosystem II complex. Here we performed a detailed characterization of UV-A-induced damage in photosystem II membrane particles using EPR spectroscopy and chlorophyll fluorescence measurements. UV-A irradiation results in the rapid inhibition of oxygen evolution accompanied by the loss of the multiline EPR signal from the S(2) state of the water-oxidizing complex. Gradual decrease of EPR signals arising from the Q(A)(-)Fe(2+) acceptor complex, Tyr-D degrees, and the ferricyanide-induced oxidation of the non-heme Fe(2+) to Fe(3+) is also observed, but at a significantly slower rate than the inhibition of oxygen evolution and of the multiline signal. The amplitude of Signal II(fast), arising from Tyr-Z degrees in the absence of fast electron donation from the Mn cluster, was gradually increased during the course of UV-A treatment. However, the amount of functional Tyr-Z decreased to a similar extent as Tyr-D as shown by the loss of amplitude of Signal II(fast) that could be measured in the UV-A-treated particles after Tris washing. UV-A irradiation also affects the relaxation of flash-induced variable chlorophyll fluorescence. The amplitudes of the fast (600 micros) and slow (2 s) decaying components, assigned to reoxidation of Q(A)(-) by Q(B) and by recombination of (Q(A)Q(B))(-) with donor side components, respectively, decrease in favor of the 15-20 ms component, which reflects PQ binding to the Q(B) site. In the presence of DCMU, the fluorescence relaxation is dominated by a 1 s component due to recombination of Q(A)(-) with the S(2) state. After UV-A radiation, this is partially replaced by a much faster component (30-70 ms) arising from recombination of Q(A)(-) with a stabilized intermediate PSII donor, most likely Tyr-Z degrees. It is concluded that the primary damage site of UV-A irradiation is the catalytic manganese cluster of the water-oxidizing complex, where electron transfer to Tyr-Z degrees and P(680)(+) becomes inhibited. Modification and/or inactivation of the redox-active tyrosines and the Q(A)Fe(2+) acceptor complex are subsequent events. This damaging mechanism is very similar to that induced by the shorter wavelength UV-B (280-320) radiation, but different from that induced by the longer wavelength photosynthetically active light (400-700 nm).

BackgroundSynechocystis sp. PCC 6803, a model organism used for bioenergy and bioplastic production, was grown in continuous culture to assess its most important bioenergetic parameters.ResultsBiomass yield on light energy of 1.237 g mol photons−1 and maintenance energy requirement of 0.00312 mol photons g−1 h−1 were calculated. This corresponded to a light conversion efficiency of 12.5 %, based on the model of Pirt which was about 35 % lower than the theoretical one based on the stoichiometric equation for the formation of biomass on carbon dioxide, water, and nitrate. The maximum Fv/Fm ratio recorded in the Synechocystis cultures was 0.57; it progressively declined to 0.45 as the dilution rate increased. An over-reduction of reaction centers at a high dilution rate was also recorded, together with an increased VJ phase for the chlorophyll fluorescence transient. In contrast, the chlorophyll optical cross section increased by about 40 % at the fastest dilution rate, and compensated for the decline in Fv/Fm, thus resulting in a constant total photosynthesis rate (photosynthesis plus respiration). Chlorophyll content was maximum at the lowest dilution rate and was 48 % lower at the highest one, while phycocyanin, and total carotenoids decreased by about 42 % and 37 %, respectively. Carotenoid analysis revealed increased echinenone, zeaxanthin, and myxoxanthophyll contents as the dilution rate increased (40.6, 63.8 and 35.5 %, respectively, at the fastest dilution rate). A biochemical analysis of the biomass harvested at each different dilution rates showed no changes in the lipid content (averaging 11.2 ± 0.6 % of the dry weight), while the protein content decreased as the dilution rate increased, ranging between 60.7 ± 1.1 and 72.6 ± 0.6 %. Amino acids pattern did not vary with the dilution rate. Carbohydrate content ranged from 9.4 to 16.2 % with a mean value of 11.2 ± 1.4 %.ConclusionsThe present work provides useful information on the threshold of light conversion efficiency in Synechocystis, as well as basic bioenergetic parameters that will be helpful for future studies related to its genetic transformation and metabolic network reconstruction.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-015-0319-7) contains supplementary material, which is available to authorized users.

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One of the limits of current electrochemical biosensors is a lack of methods providing stable and highly efficient junctions between biomaterial and solid-state devices. This paper shows how laser-induced forward transfer (LIFT) can enable efficient electron transfer from photosynthetic biomaterial immobilized on screen-printed electrodes (SPE). The ideal pattern, in terms of photocurrent signal of thylakoid droplets giving a stable response signal with a current intensity of approximately 335 ± 13 nA for a thylakoid mass of 28 ± 4 ng, was selected. It is shown that the efficiency of energy production of a photosynthetic system can be strongly enhanced by the LIFT process, as demonstrated by use of the technique to construct an efficient and sensitive photosynthesis-based biosensor for detecting herbicides at nanomolar concentrations.

A novel, type 1 ribosome‐inactivating protein designated charybdin was isolated from bulbs of Charybdis maritima agg. The protein, consisting of a single polypeptide chain with a molecular mass of 29 kDa, inhibited translation in rabbit reticulocytes with an IC50 of 27.2 nm. Plant genomic DNA extracted from the bulb was amplified by PCR between primers based on the N‐terminal and C‐terminal sequence of the protein from dissolved crystals. The complete mature protein sequence was derived by partial DNA sequencing and terminal protein sequencing, and was confirmed by high‐resolution crystal structure analysis. The protein contains Val at position 79 instead of the conserved Tyr residue of the ribosome‐inactivating proteins known to date. To our knowledge, this is the first observation of a natural substitution of a catalytic residue at the active site of a natural ribosome‐inactivating protein. This substitution in the active site may be responsible for the relatively low in vitro translation inhibitory effect compared with other ribosome‐inactivating proteins. Single crystals were grown in the cold room from PEG6000 solutions. Diffraction data collected to 1.6 Å resolution were used to determine the protein structure by the molecular replacement method. The fold of the protein comprises two structural domains: an α + β N‐terminal domain (residues 4–190) and a mainly α‐helical C‐terminal domain (residues 191–257). The active site is located in the interface between the two domains and comprises residues Val79, Tyr117, Glu167 and Arg170.