Elucidating butanol tolerance mediated by a response regulator Sll0039 in Synechocystis sp. PCC 6803 using a metabolomic approach.

Butanol is highly toxic to cyanobacterial cells, which could restrict the future application of this renewable system in producing carbon neutral biofuel butanol. To seek knowledge regarding butanol tolerance in cyanobacteria, a library of response regulator (RR) gene mutants of Synechocystis sp. PCC 6803 was screened. The results showed that the deletion mutant of an orphan RR-encoding genes ll0039 was more sensitive to butanol than the wild type, while complementation of the ∆slr1037 mutant with the sll0039 gene recovered its tolerance to the same level as the wild type, suggesting that the sll0039 gene was involved in the regulation of tolerance against butanol. Further analysis employing an integrated liquid chromatography-mass spectrometry (LC-MS)-based and gas chromatography-mass spectrometry (GC-MS)-based metabolomics was conducted to determine the possible regulatory network of butanol tolerance mediated by Sll0039. LC-MS analysis allowed the identification of several metabolites, such as adenosine 5'-diphosphate (ADP)-glucose, dihydroxyacetone phosphate (DHAP), D-ribose 5-phosphate (R5P), D-glucose 6-phosphate (G6P), D-fructose 6-phosphate (F6P), α-ketoglutaric acid (AKG), uridine 5'-diphospho (UDP)-glucose, and nicotinamide adenine dinucleotide phosphate (NADP), which were differentially regulated between the wild type and the ∆sll0039 mutant grown under butanol stress, while GC-MS analysis identified 1, 2, and 2 metabolic modules associated with the sll0039 gene deletion at 24, 48, and 72 h, respectively, suggesting that they were under control directly or indirectly by Sll0039 RR. In addition, a metabolomic comparison of the metabolic responses to butanol stress was conducted in the ∆sll0039 mutant and the ∆slr1037 mutant previously found to be involved in butanol tolerance (Chen et al. Biotechnol Biofuels 7:89 2014a), and the results showed that the regulatory networks mediated by Sll0039 and Slr1037 could be functionally independent in Synechocystis. The results provided a metabolomic description of the butanol tolerance network regulated by Sll0039.