Abstract
The effect of phycobilisome antenna-truncation in the cyanobacterium Synechocystis sp. PCC 6803 on biomass production and glycogen accumulation have not yet been fully clarified. To investigate these effects here, the apcE gene, which encodes the anchor protein linking the phycobilisome to the thylakoid membrane, was deleted in a glucose tolerant strain of Synechocystis sp. PCC 6803. Biomass production of the apcE-deleted strain under photoautotrophic and atmospheric air conditions was 1.6 times higher than that of strain PCC 6803 (1.32 ± 0.01 versus 0.84 ± 0.07 g cell-dry weight L−1, respectively) after 15 days of cultivation. In addition, the glycogen content of the apcE-deleted strain (24.2 ± 0.7%) was also higher than that of strain PCC 6803 (11.1 ± 0.3%). Together, these results demonstrate that antenna truncation by deleting the apcE gene was effective for increasing biomass production and glycogen accumulation under photoautotrophic and atmospheric air conditions in Synechocystis sp. PCC 6803.
Highlights
Biorefinery processes that convert sustainable biomass into commercially valuable chemical and energy sources have received increasing attention because of depleting fossil fuel reserves and concerns about the accumulation of greenhouse gases (Hasunuma et al 2013a)
The ΔapcE mutant gave a single amplicon of 2.0 kb, confirming the deletion of the apcE gene and insertion of the kanamycin cassette, whereas GT produced an amplicon of 3.6 kb corresponding to the apcE gene (Figure 1a)
The relative amount of chlorophyll in the ΔapcE mutant and wild-type GT were similar. These results suggested that deletion of the apcE gene, which would have impaired phycobilisome assembly and attachment, does not affect the amount of chlorophyll in cells
Summary
Biorefinery processes that convert sustainable biomass into commercially valuable chemical and energy sources have received increasing attention because of depleting fossil fuel reserves and concerns about the accumulation of greenhouse gases (Hasunuma et al 2013a). The rate of photon absorption by the chlorophyll antenna molecules in the surface layer of microalgal and cyanobacterial cells in cultures or pond environments exceeds the rate of photosynthetic reactions, resulting in the dissipation or loss of excess photons and/or photoinhibition of photosynthesis (Melis 2009). It was shown that a truncated chlorophyll antenna mutant of the green alga Chlamydomonas reinhardtii exhibited reduced absorbance of light by the first layers of cells and alleviated photoinhibition, resulting in high biomass production (Polle et al 2003)
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