Phycobilisome-Deficient Strains of Synechocystis sp. PCC 6803 Have Reduced Size and Require Carbon-Limiting Conditions to Exhibit Enhanced Productivity. Issue 2 (23rd April 2014)

• Record Type: Journal Article
• Authors: Lea-Smith, David J.; Bombelli, Paolo; Dennis, John S.; Scott, Stuart A.; Smith, Alison G.; Howe, Christopher J.
• Is Part Of: Plant physiology. Volume 165:Issue 2(2014)
• Page Start: 705
• Page End: 714
• Publication Date: 2014-04-23
• Subjects: Plant physiology -- Periodicals; Botany -- Periodicals; Periodicals; Electronic journals; 571.2
• DOI: 10.1104/pp.114.237206
• Languages: English
• ISSNs: 0032-0889

Abstract

Abstract : Gradual reduction of the light-harvesting complex in Synechocystis, the phycobilisome, results in decreased cell size and chlorophyll levels, lower photosynthesis, photoinhibition, and respiration, with increased productivity and biomass accumulation under carbon-limited conditions . Abstract: Reducing excessive light harvesting in photosynthetic organisms may increase biomass yields by limiting photoinhibition and increasing light penetration in dense cultures. The cyanobacterium Synechocystis sp. PCC 6803 harvests light via the phycobilisome, which consists of an allophycocyanin core and six radiating rods, each with three phycocyanin (PC ) discs. Via targeted gene disruption and alterations to the promoter region, three mutants with two (pcpc T→C) and one (ƊCpcC1C2:pcpc T→C) PC discs per rod or lacking PC (olive) were generated. Photoinhibition and chlorophyll levels decreased upon phycobilisome reduction, although greater penetration of white light was observed only in the PC -deficient mutant. In all strains cultured at high cell densities, most light was absorbed by the first 2 cm of the culture. Photosynthesis and respiration rates were also reduced in the ƊCpcC1C2:pcpc T→C and olive mutants. Cell size was smaller in the pcpc T→C and olive strains. Growth and biomass accumulation were similar between the wild-type and pcpc T→C under a variety of conditions. Growth and biomass accumulation of the olive mutant were poorer in carbon-saturated cultures but improved in carbon-limited cultures at higher light intensities, as they did in the ƊCpcC1C2:pcpc T→C mutant. This study shows that one PC disc per rod is sufficient for maximal light harvesting and biomass accumulation, except under conditions of high light and carbon limitation, and two or more are sufficient for maximal oxygen evolution. To our knowledge, this study is the first to measure light penetration in bulk cultures of cyanobacteria and offers important insights into photobioreactor design.