3-Hydroxy propionate pathway, used e.g. by phototrophic green non-sulphur bacteria. Fractionation

Uses bicarbonate instead of CO2, it is more positive by about 7-8 permille than CO2 – so bacteria using this will already be more positive from the start -> biomass lil. depleted vs CO2, alkyl enriched vs CO2, isoprenoids more depleted compared to alkyl and biomass