Proteome turnover in growth-arrested cyanobacteria and implications for prolonging product synthesis
Type: article
Abstract: Restricted growth due to nutrient limitation is a natural state for microbes. The resulting metabolic reprogramming facilitates survival while preparing for resuscitation. In bioproduction, artificially induced growth arrest can be used to divert metabolic flux toward synthesis of chemicals. Here, we investigated two means for inducing growth arrest in the model cyanobacterium Synechocystis sp. PCC 6803. As a natural growth arrest, we induced the stringent response by overexpressing a variant of the (p)ppGpp synthetase RelA+ from E. coli. As an artificial growth arrest, we used CRISPR interference to suppress citrate synthase, an enzyme essential for amino acid synthesis. Both strains showed increased specific productivity of heterologous lactate, but only the RelA+ produced stably for > 7 d. The stringent response allowed strains to maintain photosynthesis proteins while decreasing ribosome content, whereas CRISPRi led to a decrease in photosynthesis proteins. We studied protein turnover using dynamics of a YFP reporter and time resolved proteomics of 15N nitrate incorporation. Induction of protein synthesis in growth-arrested cells showed two populations with low and high synthesis capacity. Cells experiencing a stringent response did not assimilate exogenous nitrate, but they did cycle proteins. By contrast, cells that were growth arrested by CRISPRi were able to assimilate exogenous nitrate. Many proteins showed concerted changes in protein turnover during growth arrest, such as more stable phasin proteins. The RNA polymerase sigma factor was particularly stabilized in the RelA strain. The ability to degrade and synthesize internal proteins may contribute to the observed extended metabolic activity during the stringent response in Synechocystis. Modulation of protein cycling could be an avenue for increasing or extending metabolic activity during growth arrest.
Authors: Knave, Axel, Sporre, Emil, Hudson, Elton P.
Language: English
Subfield: Molecular Biology
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W7130494877