Phenotypic characterization of Synechocystis sp. PCC 6803 substrains reveals differences in sensitivity to abiotic stress

Abstract

Synechocystis sp. PCC 6803 is a widely used model cyanobacterium, whose substrains can vary on both genotype and phenotype levels. Previously described phenotypic variations include ability of mixotrophic growth, ability of movement on agar plates and variations in pigments composition or cell size. In this study, we report for the first time significant variation among Synechocystis substrains in complex cellular traits such as growth rate, photosynthesis efficiency, cellular dry weight and cellular composition (including protein or carbohydrates content). We also confirmed previously reported differences in cell size. Synechocystis cultures were cultivated in controlled environment of flat panel photobioreactors under red, blue and white light of intensities up to 790 μmol(photons) m-2 s-1, temperatures 23°C–60°C, input CO2 concentrations ranging from 400 to 15 000 ppm and in BG11 cultivation medium with and without addition of NaCl. Three Synechocystis substrains were used for the comparative experiments: GT-L, GT-B (Brno, CZ) and PCC-B (Brno, CZ). Growth rates of Synechocystis GT-B were inhibited under high intensities of red light (585–670 nm), and growth rates of both substrains GT-B and PCC-B were inhibited under photons of wavelengths 485–585 nm and 670–700 nm. Synechocystis GT-B was more sensitive to low temperatures than the other two tested substrains, and Synechocystis GT-L was sensitive to the presence of NaCl in the cultivation media. The results suggest that stress sensitivity of commonly used Synechocystis substrains can strongly vary, similarly as glucose tolerance or motility as reported previously. Our study further supports the previous statement that emphasizes importance of proper Synechocystis substrains selection and awareness of phenotypical differences among Synechocystis substrains which is crucial for comparative and reproducible research. This is highly relevant for studies related to stress physiology and development of sustainable biotechnological applications.

Quantitative insights into the cyanobacterial cell economy

“…The increase in gas exchange (O 2 release and basal respiration) has been observed previously. Likewise, the increase in cellular size with growth rate (Figure 2A) has been reported in Synechocystis (Zavřel et al, 2017;Cordara et al, 2018) as well as in bacteria, yeast or mammalian cells (Aldea et al, 2017). Light was also shown to affect DNA content (ploidy level) in Synechocystis (Zerulla et al, 2016), however, no study of DNA content change with growth rate is available to date.…”

“…PCC 6803 GT-L phenotype throughout a four year period (2013 -2017). Figure 1D and 1E show a comparison of the specific growth, as well as photosynthetic and respiration rates, from several previous studies (Zavřel et al, 2015b(Zavřel et al, , 2017 and as yet unpublished data.…”

“…(D) Comparison of specific growth rates using an identical experimental setup throughout four successive years 2013 -2017 (source data are available in Figure 1 -Source data 2). (E) Comparison of photosynthetic and respiration rates (measured as O2 evolution and consumption rates within the photobioreactor vessel throughout light and dark periods in 2016 -2017 (this study) and in 2015 -2017 (Zavřel et al, 2017). The dashed line represents a P-I curve fit of data from this study according to Platt T. , Gallegos C.L., Harrison W.G.…”

“…(see Figure 1 -Figure supplement 1). The experimental setup, including the photobioreactor setup, light quality and intensity, temperature, composition of cultivation medium, CO 2 concentration in sparging gas, bubbling and stirring rate was identical to the setup used in previous studies for this substrain (Zavřel et al, 2015b(Zavřel et al, , 2017. We therefore could evaluate the stability of the Synechocystis sp.…”

“…PCC 6803 (Synechocystis hereafter). Since Synechocystis exhibits significant variations with respect to genotype (Ikeuchi and Tabata, 2001) and phenotype (Morris et al, 2016;Zavřel et al, 2017), we chose the substrain GT-L, a strain that has a documented stable phenotype for at least four years preceding this study. All data are obtained under highly reproducible and controlled experimental conditions, using flat-panel photobioreactors (Nedbal et al, 2008) within an identical setup as in previous studies (Zavřel et al, 2015b).…”