Purple phototrophic bacteria (PPB) can be used to convert gaseous streams (e.g., H2 and CO2) into single-cell protein. This work aimed to determine the specific uptake rates of enriched/mixed PPB cultures under different environmental conditions (i.e., temperatures, pH and light intensities), using a mechanistic model considering relevant biological and physico-chemical processes. The model accurately represented results from batch tests with different gas-transfer kinetics (i.e., kLa values), providing similar biological uptakes rates. Optimal rates of 1.9-2.0 g COD•g COD-1 •d-1 were reached at pH 7, 25ºC and light intensities over 30 W•m-2 , with biomass yields of ~1 g COD⸱g-1 COD. The influence of light and temperature on the uptake rates was modelled using the Steele's equation and the cardinal temperature model with inflection. The obtained rates are similar to those for pure PPB cultures and those achieved via photoheterotrophy.