Towards sustainable aquafeeds: Safe and consistent microbial protein grown on food-processing wastewater

• Microbial community-based SCP grown on soybean wastewater was consistent. • SCP was safe for fish due to very low abundance of fish-pathogen-like sequences. • SCP contained essential amino acids to supplement conventional animal diet. • Azospirillum , a nitrogen-fixing bacterium, was the prevalent taxon in all replicates. • Replicates showed similar patterns of biomass growth and protein accumulation. Microbial community-based single cell protein (SCP) holds promise as a sustainable source of protein in livestock feed; yet its feed-safety and consistency in composition and production when using variable real-world wastewater has not been investigated. Here, the effect of heterogeneity in soybean-processing wastewater on SCP quality was tested using four replicate sequencing batch reactors over 92 days. The microbial community-based SCP grown on soybean wastewater demonstrated high consistency, with replicates showing similar patterns of biomass growth and protein accumulation. The dry microbial biomass exhibited a protein content of 39.8 ± 5.8 %, and the yield was 17.7 ± 1.7 g dry weight/g soluble total Kjeldahl nitrogen (sTKN). Azospirillum , a nitrogen-fixing bacterium, was the prevalent SCP-producing genus in all replicates at a relative abundance of 40.6 ± 5.1 %. The organism was not detected in wastewater, where Lactococcus and Weissella dominated. SCP contained essential amino acids to supplement conventional animal diets and was deemed safe for fish due to the very low abundance of fish-pathogen-like sequences (< 0.009 %) via metabarcoding. This study demonstrates the consistency of microbial community-based SCP derived from food-processing wastewater and addresses feed safety through pathogen screening, highlighting its potential to substitute protein in traditional animal feed and contribute to sustainable aquaculture practices.