Fig. 4. Usability of different molecular tools for the expression of heterologous proteins in Synechococcus sp. PCC 11901.

a Schematic illustration of constructs used for natural transformation and homologous recombination in the chromosome of 11901 strain. In the pSW036 vector the yfp gene was inserted between 700 bp flanking regions of the acsA gene and expression was controlled by the synthetic and constitutive P_cpt promoter. In the pSW039 vector, the yfp gene (under control of the synthetic, inducible P_clac143 promoter) together with the lacI regulator and a spectinomycin-resistance cassette were inserted between 700 bp flanking regions of the psbA2 gene. b Fluorescence microscopy images of cells transformed with YFP constructs. As a control, chlorophyll a autofluorescence of WT, ΔacsA::P_cpt-YFP and ΔpsbA2::P_clac143-YFP is shown on the left side of the panel, and YFP fluorescence is shown in the middle panel. ΔpsbA2::P_clac143-YFP strain was incubated for 24 h with/without addition of 1 mM IPTG prior to imaging. Scale 10 µm. c Strength and inducibility comparison of P_cpt and P_clac143 promoters. Relative YFP fluorescence in relation to OD₇₃₀ was measured for cultures at OD ≈ 1 (T = 0), after 6 and 24 h. The bars represent mean of n = 3 biological replicates ±standard deviation.