Available online 29 August 2022
HIGHLIGHTS•Ten photoautohydrogenotrophic species were enriched from water treatment microbiomes
•Repeated subcultivation improved maximum growth rates and protein productivities
•Metabolic carbon/electron switches decreased protein productivity and pigment content
•All tested purple bacteria could provide full human dietary protein matches
•Photoheterotrophically enriched species act as photoautohydrogenotrophic specialist
AbstractPhotoautohydrogenotrophic enrichments of wastewater treatment microbiomes were performed to obtain hypothetically high-potential specialist species for biotechnological applications. From these enrichment cultures, ten photoautohydrogenotrophic species were isolated: six Rhodopseudomonas species, three Rubrivivax members and Rhodobacter blasticus. The performance of these isolates was compared to three commonly studied, and originally photoheterotrophically enriched species (Rhodopseudomonas palustris, Rhodobacter capsulatus and Rhodobacter sphaeroides), designated as reference species. Repeated subcultivations were applied to improve the initial poor performance of the isolates (acclimation effect), which resulted in increases in both maximum growth rate and protein productivity. However, the maximum growth rate of the reference species remained 3-7 times higher compared to the isolates (0.42-0.84 d-1 at 28°C), while protein productivities remained 1.5-1.7 times higher. This indicated that H2-based enrichment did not result in photoautohydrogenotrophic specialists, suggesting that the reference species are more suitable for intensified biomass and protein production. On the other hand, the isolates were able to provide equally high protein quality profiles as the references species, providing full dietary essential amino acid matches for human food. Lastly, the effect of metabolic carbon/electron switching (back and forth between auto- to heterotrophic conditions) initially boosted µmax when returning to photoautohydrogenotrophic conditions. However, the switch negatively impacted lag phase, protein productivities and pigment contents. In the case of protein productivity, the acquired acclimation was partially lost with decreases of up to 44% and 40% respectively for isolates and reference species. Finally, the three reference species, and specifically Rh. capsulatus, remained the most suitable candidate(s) for further biotechnological development.
AbbreviationsPAH2Photoautohydrogenotrophy
KsSubstrate affinity constant
VFA(Volatile fatty acids)
CODChemical oxygen demand
PHVFAPhotoheterotrophic with VFA as carbon source
TSSTotal suspended solids
VSSVolatile suspended solids
EAAIEssential amino acids index
Bchl aBacteriochlorophyll a
HOBHydrogen oxidizing bacteria
KeywordsSingle-cell protein
Hydrogen economy
CO2 economy
Purple non-sulphur bacteria
Phototrophic purple bacteria
Essential amino acids
© 2022 Published by Elsevier B.V.
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