Figure 1

GFP activity driven by different promoters on different carbon sources. GFP fluorescence, culture pH and biomass accumulation (OD₆₀₀) of the P _TEF1 -yEGFP strain (a) and the P _TEF1 -yEGFP-CLN2 _PEST strain (b) in flask batch cultivation in YNB broth with 20 g L⁻¹ glucose as the carbon source are shown. GFP fluorescence of various promoter-yEGFP-CLN2 _PEST strains on 20 g L⁻¹ glucose in microtitre plate culture (c) and of various promoter-yEGFP strains on various carbon sources in microtitre plate culture (d) are also shown. The GFP fluorescence in (c) was ranged using Tukey’s test: three levels were identified (dashed lines a > b > c) within which the difference between group members (bold lines) was insignificant (p > 0.05). In TEF1-M (d) construction, A XhoI site plus triple “A” was inserted between TEF1 promoter and the start codon of yEGFP. The insert in (d) shows a zoomed-in GFP fluorescence scale for the weaker promoters, P _PDA1 , P _CYC1 , P _TPS1 and P _CUP1 . The analysis of variance for the fluorescence levels in (d) is shown in Additional file 1: Figure S3. The auto-fluorescence was determined from the reference strains (ILHA GH4 for the yEGFP strains and ILHA GFP3 for the yEGFP-CLN2 _PEST strains) in parallel. Symbol Asterisk represents that the value is <50 and not significantly different from auto-fluorescence (t test, p > 0.05). Mean values ± standard deviations are shown from replicate cultivations.