title: Environmental pH affects photoautotrophic growth of Synechocystis sp. PCC 6803 strains carrying mutations in the lumenal proteins of PSII.
abstract: Synechocystis sp. strain PCC 6803 grows photoautotrophically across a broad pH range, but wild-type cultures reach a higher density at elevated pH; however, photoheterotrophic growth is similar at high and neutral pH. A number of PSII mutants each lacking at least one lumenal extrinsic protein, and carrying a second PSII lumenal mutation, are able to grow photoautotrophically in BG-11 medium at pH 10.0, but not pH 7.5. We investigated the basis of this pH effect and observed no pH-specific change in variable fluorescence yield from PSII centers of the wild type or the pH-dependent ΔPsbO:ΔPsbU and ΔPsbV:ΔCyanoQ strains; however, 77 K fluorescence emission spectra indicated increased coupling of the phycobilisome (PBS) antenna at pH 10.0 in all mutants. DNA microarray data showed a cell-wide response to transfer from pH 10.0 to pH 7.5, including decreased mRNA levels of a number of oxidative stress-responsive transcripts. We hypothesize that this transcriptional response led to increased tolerance against reactive oxygen species and in particular singlet oxygen. This response enabled photoautotrophic growth of the PSII mutants at pH 10.0. This hypothesis was supported by increased resistance of all strains to rose bengal at pH 10.0 compared with pH 7.5.
authors: Department of Botany, University of Otago, PO Box 56, Dunedin, 9054, New Zealand. tina.summerfield@otago.ac.nz
authors: Tina C
authors: TC
authors: Summerfield
authors: Tim S
authors: TS
authors: Crawford
authors: Roger D
authors: RD
authors: Young
authors: Jocelyn P S
authors: JP
authors: Chua
authors: Rebecca L
authors: RL
authors: Macdonald
authors: Louis A
authors: LA
authors: Sherman
authors: Julian J
authors: JJ
authors: Eaton-Rye
mesh_terms: D052818:Autotrophic Processes / Q000187:drug effects / Q000528:radiation effects*; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D002021:Buffers; D002734:Chlorophyll / Q000378:metabolism; D000077194:Chlorophyll A; D003470:Culture Media / Q000494:pharmacology; D004777:Environment; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects / Q000528:radiation effects; D005798:Genes, Bacterial / Q000235:genetics; D052836:Heterotrophic Processes / Q000187:drug effects / Q000528:radiation effects; D006863:Hydrogen-Ion Concentration / Q000187:drug effects; D007700:Kinetics; D008954:Models, Biological; D009154:Mutation / Q000235:genetics*; D018384:Oxidative Stress / Q000187:drug effects / Q000235:genetics / Q000528:radiation effects; D045332:Photosystem II Protein Complex / Q000235:genetics* / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012395:Rose Bengal / Q000494:pharmacology; D026082:Singlet Oxygen / Q000494:pharmacology; D013050:Spectrometry, Fluorescence; D046939:Synechocystis / Q000187:drug effects / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism; D014158:Transcription, Genetic / Q000187:drug effects / Q000528:radiation effects
chemical_list: D001426:Bacterial Proteins; D002021:Buffers; D003470:Culture Media; D045332:Photosystem II Protein Complex; D012333:RNA, Messenger; D002734:Chlorophyll; D026082:Singlet Oxygen; D012395:Rose Bengal; D000077194:Chlorophyll A
keywords: Alkaline pH; Gene expression; Oxidative stress; PSII extrinsic proteins; Photosynthesis; Synechocystis sp. PCC 6803