Part:BBa_K4370000:Experience
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Applications of BBa_K4370000
We performed experiments to evaluate the activity of Streptomyces bottropensis RuBisCO in native and heterologous chassis.
S. bottropensis ATCC 25435 strain was grown during 4 days in sub-minimal liquid medium (devoid of carbon source), minimal liquid medium 0.5 % glycerol and rich liquid medium (MP5), under standard atmosphere or 3 % CO2 enriched atmosphere (in jar containing BD GasPak EZ) at 30°C under agitation. E. coli BL21DE3 strains were grown in LB rich liquid medium during 24 h at 20°C under agitation.
Cell extracts were prepared following a protocol very similar to the one proposed by the iGEM Bielefeld 2014 team (https://2014.igem.org/Team:Bielefeld-CeBiTec/Results/CO2-fixation/RuBisCO), except that cells were lysed One Shot Cell Disrupters (Constant Systems Ltd - 2.5 kbar). Our precise protocol is available here: File:T--Go-Paris-Saclay-protocol-RuBisCO.pdf
We thus performed a RuBisCO activity test on S. bottropensis ATCC 25435 and E. coli BL21DE3 strains harboring a plasmid encoding ccbL (BBa_K4370000, BBa_K4370002) and cbbS (BBa_K4370001, BBa_K4370003) under the control of tetO promoter (BBa_R0040) or a control plasmid (containing BBa_K4370010). The background in the E. coli extracts in the analysis area makes the result inconclusive (Figure 1).
However, we obtained interesting results in S. bottropensis background. First, we noticed that the final biomass reached by S. bottropensis in sub-minimal liquid medium under 3 % CO2 enriched atmosphere was twice the final biomass reached in this medium in a standard atmosphere. Such a doubling in the biomass under enriched atmosphere was not observed with another Streptomyces grown in the same conditions (Figure 2). This result suggests that at least in one condition (absence of carbon source and under 3 % CO2), S. bottropensis may fix CO2 to form biomass. This observation supports the hypothesis that its CO2 fixation module encodes a functional RuBisCO that is expressed under these conditions.
Our HPLC analysis of the signal detected in the UV (220 nm) allows to detect both the substrate (RuBP, ribulose-1,5-bisphosphate) and the product (PGA, 3-phosphoglycerate), used as standards. After around 1 min incubation at room temperature of RuBP with cell extract, the RuBP was not detected in all S. bottropensis samples (Figure 3), suggesting that it was used by some enzymes (… that may be RuBisCO!). To be sure that the RuBP was consumed by the RuBisCO, we needed to detect the product of this enzyme (PGA). Interestingly, a signal was detected at the retention time of the PGA only in the sub-minimal medium (devoid of carbon source) under standard atmosphere. Neither RuBP nor GPA was detected in the reaction using cell extract of cells grown in this medium under 3 % CO2 enriched atmosphere. This suggests that if GPA was produced in this condition, it was used by other cellular enzymes to produce compounds not detected in our window of analysis. These enzymes could be other enzymes encoded by the CO2 fixation module of S. bottropensis and/or its endogenous pentose phosphate pathway. We note a significant baseline in some samples which can make the results ambiguous. Thus the determination of the nature of the products by mass spectrometry could allow to confirm the identity of the product and therefore these first results.
Taken together, these results provide for the first time preliminary data in favour of the functionality of a Streptomyces RuBisCO, which will need to be confirmed by further analyses.
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