Potential of enriched phototrophic purple bacteria for H2 bioconversion into single cell protein

Single cell protein (SCP) has emerged as an alternative protein source, potentially based on the recovery of carbon and nutrients from waste-derived resources as part of the circular economy. From those resources, gaseous substrates have the advantage of an easy sterilization, allowing the production of pathogen-free SCP. Sterile gaseous substrates allow producing pathogen-free SCP. This study evaluated the use of an enriched phototrophic purple bacteria (PPB) consortium for SCP production using H-2 and CO2 as electron and C sources. The influence of pH (6.0-8.5), temperature (15-50 degrees C) and light intensity (0-50 W center dot m(-2)) on the growth kinetics and biomass yields was investigated using batch tests. Optimal conditions were found at pH 7, 25 degrees C and light intensities over 30 W center dot m(-2). High biomass and protein yields were achieved (similar to 1 g CODbiomass center dot g CODH2consumed-1 and 3.9-4.4 g protein center dot g H-2(-1)) regardless of the environmental conditions, being amongst the highest values reported from gaseous streams. These high yields were obtained thanks to the use of light as a sole energy source by the PPB consortium, allowing a total utilization of H-2 for growth. Hydrogen uptake rates varied considerably, with values up to 61 +/- 5 mg COD center dot d(-1) for the overall H-2 consumption rates and 2.00 +/- 0.14 g COD center dot g COD-1 center dot d(-1) for the maximum specific uptake rates under optimal growth conditions. The latter value was estimated using a mechanistic model able to represent PPB growth on H-2. The biomass exhibited high protein contents (>50 % w/w) and adequate amino acid profiles, showing its suitability as SCP for feed. PPB were the dominant bacteria during the experiments (relative abundance over 80 % in most tests), with a stable population dominated by Rhodobacter sp. and Rhodopseudomonas sp. This study demonstrates the potential of enriched PPB cultures for H-2 bioconversion into SCP.