Simultaneous increases in the levels of compatible solutes by cost‐effective cultivation of Synechocystis sp. PCC 6803

Abstract

Synechocystis sp. PCC 6803, a cyanobacterium widely used for basic research, is often cultivated in a synthetic medium, BG-11, in the presence of 4-(2hydroxyethyl)-1-piperazine ethanesulfonic acid (HEPES) or 2-[[1,3-dihydroxy-2-(hydroxymethyl)propan-2-yl]amino]ethanesulfonic acid buffer. Owing to the high cost of HEPES buffer (96.9% of the total cost of BG-11 medium), the biotechnological application of BG-11 is limited. In this study, we cultured Synechocystis sp. PCC 6803 cells in BG-11 medium without HEPES buffer and examined the effects on the primary metabolism. Synechocystis sp. PCC 6803 cells could grow in BG-11 medium without HEPES buffer after adjusting for nitrogen sources and light intensity; the production rate reached 0.54 g cell dry weight/L/day, exceeding that of commercial cyanobacteria and Synechocystis sp. PCC 6803 cells cultivated under other conditions. The exclusion of HEPES buffer markedly altered the metabolites in the central carbon metabolism; particularly, the levels of compatible solutes, such as sucrose, glucosylglycerol, and glutamate were increased. Although the accumulation of sucrose and glucosylglycerol under high salt conditions is antagonistic to each other, these metabolites accumulated simultaneously in cells grown in the cost-effective medium. Because these metabolites are used in industrial feedstocks, our results reveal the importance of medium composition for the production of metabolites using cyanobacteria.

Heterologous Production of Glycine Betaine Using Synechocystis sp. PCC 6803-Based Chassis Lacking Native Compatible Solutes

“…In contrast, glutamate could be detected in the absence and presence of NaCl (Figure 2). These results are in agreement with the reported accumulation of this amino acid in Synechocystis grown in artificial seawater medium (ASW; 340 mM NaCl), and in BG11 supplemented with 12 mM KCl (Iijima et al, 2015;Iijima et al, 2020).…”

“…Moreover, various molecular and synthetic biology tools are now available for the genetic manipulation and engineering of this particular cyanobacterial strain (Huang et al, 2010;Heidorn et al, 2011;Pinto et al, 2015;Pacheco et al, 2021). Synechocystis is a freshwater strain and thus moderately halotolerant, relying on the biosynthesis of the compatible solutes sucrose, glutamate and glucosylglycerol to maintain the osmotic pressure under stress conditions (Klähn and Hagemann, 2011;Iijima et al, 2020).…”

Heterologous production of glycine betaine using Synechocystis sp. PCC 6803-based chassis lacking native compatible solutes

“…2). These results are in agreement with the reported accumulation of this amino acid in Synechocystis grown in artificial seawater medium (ASW; 340 mM NaCl), and in BG11 supplemented with 12 mM KCl (40,46). Previous works have also reported a tradeoff between the pools of different compatible solutes and other carbon sinks, such as glycogen or extracellular polymeric substances (EPS) in cyanobacteria (47)(48)(49).…”

“…Moreover, various molecular and synthetic biology tools are now available for the genetic manipulation and engineering of this particular cyanobacterial strain (36)(37)(38)(39). Synechocystis is a freshwater strain and thus moderately halotolerant, relying on the biosynthesis of the compatible solutes sucrose, glutamate and glucosylglycerol to maintain the osmotic pressure under stress conditions (1,40).…”

Arginine inhibits the arginine biosynthesis rate-limiting enzyme and leads to the accumulation of intracellular aspartate in Synechocystis sp. PCC 6803

“…Under physiological conditions, the intracellular arginine concentration in Synechocystis 6803 is 0.6 mM (Zhang et al 2018 ). The intracellular arginine levels in Synechocystis 6803 change depending on the growth medium (Iijima et al 2020 ). We propose that arginine biosynthesis in Synechocystis 6803 is regulated by Sy ArgG, including the ornithine cycle, and not only by NAGK to adapt to various environments.…”