Maximizing photosynthetic efficiency and culture productivity in cyanobacteria upon minimizing the phycobilisome light-harvesting antenna size

Abstract

A phycocyanin-deletion mutant of Synechocystis (cyanobacteria) was generated upon replacement of the CPC-operon with a kanamycin resistance cassette. The Δcpc transformant strains (Δcpc) exhibited a green phenotype, compared to the blue-green of the wild type (WT), lacked the distinct phycocyanin absorbance at 625nm, and had a lower Chl per cell content and a lower PSI/PSII reaction center ratio compared to the WT. Molecular and genetic analyses showed replacement of all WT copies of the Synechocystis DNA with the transgenic version, thereby achieving genomic DNA homoplasmy. Biochemical analyses showed the absence of the phycocyanin α- and β-subunits, and the overexpression of the kanamycin resistance NPTI protein in the Δcpc. Physiological analyses revealed a higher, by a factor of about 2, intensity for the saturation of photosynthesis in the Δcpc compared to the WT. Under limiting intensities of illumination, growth of the Δcpc was slower than that of the WT. This difference in the rate of cell duplication diminished gradually as growth irradiance increased. Identical rates of cell duplication of about 13h for both WT and Δcpc were observed at about 800μmolphotonsm(-2)s(-1) or greater. Culture productivity analyses under simulated bright sunlight and high cell-density conditions showed that biomass accumulation by the Δcpc was 1.57-times greater than that achieved by the WT. Thus, the work provides first-time direct evidence of the applicability of the Truncated Light-harvesting Antenna (TLA)-concept in cyanobacteria, entailing substantial improvements in the photosynthetic efficiency and productivity of mass cultures upon minimizing the phycobilisome light-harvesting antenna size.

CRISPR interference as a titratable, trans-acting regulatory tool for metabolic engineering in the cyanobacterium Synechococcus sp. strain PCC 7002

“…In PCC 7002, the cpcBACDEF operon encodes the major components of the peripheral rods including the α-(CpcA) and β-subunits (CpcB) of phycocyanin, the rod linkers (CpcC and CpcD), and two proteins involved in attachment of the phycocyanobilin pigment to the α-phycocyanin subunit (CpcE and CpcF) (Bryant et al, 1990). Since reduction of antennae size has been a promising strategy for increasing light penetration into high-density cyanobacterial cultures (Kirst et al, 2014), we designed an sgRNA to target cpcB and inhibit transcription of the entire cpcBACDEF operon. Others have shown that when the rod proteins are deleted there is a decrease in absorbance corresponding to phycocyanin at 635 nm (Lea-Smith et al, 2014).…”

Identification and characterization of the yls mutation in rice (Oryza sativa L.) with lower photosynthetic pigment content

“…The leaves of yls mutant plants were yellow-green at the seedling stage but became progressively greener as they matured, indicating that another mechanism can compensate for the loss of the cpSRP54 pathway during the later developmental stage. One interpretation is that cpSRP43 can function independently of cpSRP54, to accomplish the thylakoid membrane assembly process (Yu et al 2012;Kirst et al 2014). …”

Redesigning photosynthesis to sustainably meet global food and bioenergy demand

“…If plants had fewer light-harvesting pigments (e.g., chlorophylls and carotenoids) per photosystem (10) and fewer photosystems in their uppermost leaves, light might be absorbed more judiciously, and a greater proportion of absorbed photons converted to biomass. This avenue has been pursued for some years in algae and cyanobacteria, often with notable success (20,21), but not yet convincingly in crop plants. Lowering leaf absorptivity remains a significant opportunity for improving crop yield (10) although it is worth noting that such highly efficient plants might be at a disadvantage under some conditions, compared with normally pigmented competitors, and could require careful plant husbandry to realize their increased yield.…”