Dingji Shi

Growth and Physiological Features of Cyanobacterium Anabaena sp. Strain PCC 7120 in a Glucose-Mixotrophic Culture

Mixotrophic growth is one potential mode for mass culture of microalgae and cyanobacteria particularly suitable for the production of high value bioactive compounds and fine chemicals. The typical heterocystous cyanobacterium Anabaena sp. PCC 7120 was grown in the presence of exogenous glucose in light. Glucose improved the cell growth evidently, the maximal specific growth rate under mixotrophic condition (0.38 d(-1)) being 1.6-fold of that of photoautotrophic growth. Mixotrophy caused a variation in cellular pigment composition, increasing the content of chlorophyll a and decreasing the contents of carotenoid and phycobiliprotein relative to chlorophyll a. Fluorescence emission from photosystem II (PSII) relative to photosystem I was enhanced in mixotrophic cells, implying an increased energy distribution in PSII. Glucokinase (EC 2.7.1.2) activity was further induced in the presence of glucose. The mixotrophic culture was scaled up in a 15 L airlift photobioreactor equipped with an inner and an outer light source. A modified Monod model incorporating the specific growth rate and the average light intensity in the reactor was developed to describe cell growth appropriately. The understanding of mixotrophic growth and relevant physiological features of Anabaena sp. PCC 7120 would be meaningful for cultivation and exploitation of this important cyanobacterial strain.

Characteristics of mixotrophic growth of Synechocystis sp. in an enclosed photobioreactor

Synechocystis sp. PCC 6803 was grown in a 2.5 l enclosed photobioreactor on medium with or without glucose. The incident light intensities ranged from 1.5 klux to 7 klux. The highest average specific growth rates of mixotrophic culture and photoautotrophic culture were, respectively, 1.3 h−1 at a light intensity of 7 klux on 3.2 g l−1 glucose and 0.3 h−1 at both light intensities of 5 klux and 7 klux. The highest cell density 2.5 g l −1 was obtained at both of light intensities 5 klux and 7 klux on 3.2 g glucose l−1. Glucose consumption decreased with decreasing light intensity. The energy yields of mixotrophic cultures were 4 to 6 times higher than that of photoautotrophic cultures. Light favored mixotrophic growth of Synechocystis sp. PCC 6803, especially at higher light intensities (5–7 klux).

Effect of iron stress, light stress, and nitrogen source on physiological aspects of marine red tide alga

Abstract Effect of iron (Fe) stress, light stress, and nitrogen (N) source on physiological aspects of the marine red tide alga Heterosigma akashiwo was investigated in batch cultures. Cellular chlorophyll and carotenoid contents increased under low light stress and decreased under iron stress. A specific pigment was induced under light stress. Nitrate reductase and nitrite reductase activities of nitrate-grown cells decreased under iron and light stress, while those of ammonium-grown cells were negligible. The cell density and the growth rate decreased under Fe stress, and this decrease can be aggravated by light stress. Compared with ammonium-grown cells, nitrate-grown cells showed an increase in the cell density and the growth rate. Intracellular C:N ratios indicated that the Fe-stress effect on nitrate or ammonium did not specifically involve in the nitrate assimilatory pathway, and light stress would aggravate the Fe-stress effect.

Regulation of pepc gene expression in Anabaena sp. PCC 7120 and its effects on cyclic electron flow around photosystem I and tolerances to environmental stresses

Since pepc gene encoding phosphoenolpyruvate carboxylase (PEPCase) has been cloned from Anabaena sp. PCC 7120 and other cyanobacteria, the effects of pepc gene expression on photosynthesis have not been reported yet. In this study, we constructed mutants containing either upregulated (forward) or downregulated (reverse) pepc gene in Anabaena sp. PCC 7120. Results from real-time quantitative polymerase chain reaction (RT-qPCR), Western blot and enzymatic analysis showed that PEPCase activity was significantly reduced in the reverse mutant compared with the wild type, and that of the forward mutant was obviously increased. Interestingly, the net photosynthesis in both the reverse mutant and the forward mutant were higher than that of the wild type, but dark respiration was decreased only in the reverse mutant. The absorbance changes of P700 upon saturation pulse showed the photosystem I (PSI) activity was inhibited, as reflected by Y(I), and Y(NA) was elevated, and dark reduction of P700(+) was stimulated, indicating enhanced cyclic electron flow (CEF) around PSI in the reverse mutant. Additionally, the reverse mutant photosynthesis was higher than that of the wild type in low temperature, low and high pH, and high salinity, and this implies increased tolerance in the reverse mutant through downregulated pepc gene.

Some physiological and biochemical changes in marine eukaryotic red tide alga Heterosigma akashiwo during the alleviation from iron limitation

Some physiological and biochemical changes in the marine eukaryotic red tide alga Heterosigma akashiwo (Hada) were investigated during the alleviation from iron limitation. Chlorophyll a/carotenoid ratio increases as a result of iron alleviation. In vivo absorption spectra of iron-limited cells showed a chlorophyll (Chl) absorption peak at 630 nm, 2 nm blue-shiftied from the normal position. Low-temperature fluorescence emission spectra of the cells have one prominent Chl emission peak at 685 nm. The cells showed a decrease in fluorescence yield from 685 nm band during alleviation from iron limitation. Low-temperature fluorescence excitation spectra and room-temperature fluorescence spectra indicated an efficient excitation energy transfer in the cells alleviated from iron limitation. Photosynthetic efficiency and carbohydrate content per cell increased after alleviation from iron limitation. Total protein decreased in iron-limited cells, while iron deficiency induced the appearance of specific soluble proteins (17 and 55 kDa)

The State Transitions and their Possible Mechanisms of Sporophytes and Gametophytes of Porphyra Yezoensis

Rencent year, two types of phycobilisomes(PBS) have been isolated from Porphyra. yezoensis, one in sporophytes and another in gametophytes, and they were obviously different in phycobiliprotein composition, molecular weight, ultrastructural morphology, and energy transfer relationships with photosystem I (PSI) and photosystem II (PSII) in vivo and in vitro[1, 2]. State transitions are redistribution of the absorbed light energy between PSI and PSII, in order to maximize the overall efficiency of photosynthesis under any light condition. In phycibilisomes-containing cells, the state transition was regulated either by the connection between phycobilisomes and thylakoinds, or by chlorophyll protein complexes of PSI and PSII. Contradictory conclusions have been derived from the mechanisms of state transition in red alga and cyanobacteria[3]. In this report different mechanisms of state transition in sporophytes and gametophytes of P. yezoensis were studied with chlorophyll fluorescence quenching analysis by performing saturation pulse methods at room temperature[4], in the presence of uncouplers and inhibitors of electron transfer.