Abstract
Physiological adaptation and genome-wide expression profiles of the cyanobacterium Synechocystis sp. strain PCC 6803 in response to gradual transitions between nitrogen-limited and light-limited growth conditions were measured in continuous cultures. Transitions induced changes in pigment composition, light absorption coefficient, photosynthetic electron transport, and specific growth rate. Physiological changes were accompanied by reproducible changes in the expression of several hundred open reading frames, genes with functions in photosynthesis and respiration, carbon and nitrogen assimilation, protein synthesis, phosphorus metabolism, and overall regulation of cell function and proliferation. Cluster analysis of the nearly 1,600 regulated open reading frames identified eight clusters, each showing a different temporal response during the transitions. Two large clusters mirrored each other. One cluster included genes involved in photosynthesis, which were up-regulated during light-limited growth but down-regulated during nitrogen-limited growth. Conversely, genes in the other cluster were down-regulated during light-limited growth but up-regulated during nitrogen-limited growth; this cluster included several genes involved in nitrogen uptake and assimilation. These results demonstrate complementary regulation of gene expression for two major metabolic activities of cyanobacteria. Comparison with batch-culture experiments revealed interesting differences in gene expression between batch and continuous culture and illustrates that continuous-culture experiments can pick up subtle changes in cell physiology and gene expression.
Highlights
Physiological adaptation and genome-wide expression profiles of the cyanobacterium Synechocystis sp. strain PCC 6803 in response to gradual transitions between nitrogen-limited and light-limited growth conditions were measured in continuous cultures
Changes in gene expression were related to changes in physiological parameters
The photosynthetic parameters aETR and ETRmax, the light attenuation coefficient k, as well as the specific growth rate m showed similar temporal variation as cluster 1, which contained many genes related to photosynthesis
Summary
Physiological adaptation and genome-wide expression profiles of the cyanobacterium Synechocystis sp. strain PCC 6803 in response to gradual transitions between nitrogen-limited and light-limited growth conditions were measured in continuous cultures. Regulation of carbon and nitrogen assimilation uses 2-oxoglutarate as a metabolic reporter, the signal protein PII as a sensing transducer, and NtcA with PipX as a transcriptional coactivator for the regulation of transcription This serves to balance gene expression to optimally sustain the enzyme activities needed for growth in nonequilibrated carbon and nitrogen supply conditions (Herrero et al, 2001; Fadi Aldehni et al, 2003; Forchhammer, 2004; Flores and Herrero, 2005; Su et al, 2005; Chen et al, 2006; Espinosa et al, 2006; Singh et al, 2008, 2009)
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