Microbial community-based production of single cell protein from soybean-processing wastewater of variable chemical composition

Abstract

The use of food-processing wastewaters to produce microbial biomass-derived single cell protein (SCP) is a sustainable way to meet the global food demand. Yet, despite the potential benefits of lower costs and greater resource recovery compared to pure cultures, bioconversion processes relying on microbial community-based approaches to SCP production have received scarce attention. Here, we evaluated SCP production from soybean-processing wastewaters under controlled reactor conditions using the existent microbial communities in these wastewaters. Six sequencing batch reactors of 4.5-L working volume were operated at 30 ℃ for 34 d in cycles consisting of 3-h anaerobic and 9-h aerobic phases. Four reactors received no microbial inoculum and the remaining two were amended with a 1.5 L of mixed culture from a prior microbial community-based SCP production. Microbial characterization was done via 16S rRNA gene metabarcoding. Influent wastewater batches had variable chemical characteristics but a similar microbial composition. Reactors produced more SCP when fed with wastewaters of higher soluble total Kjeldahl nitrogen (sTKN) content and a lower carbon-to-nitrogen ratio (sCOD:sTKN). The biomass protein yield ranged from 0.24 to 3.13 g protein/g sTKN, with a maximum protein content of 50%. An average of 92% of sCOD and 73% of sTN removal was achieved. Distinct microbial communities were enriched in all six bioreactors after 34 d, where the prevailing genera included Azospirillum, Rhodobacter, Lactococcus, Novosphingobium, and Acidipropionibacterium. In contrast, the microbial community of influent wastewaters was dominated by Lactococcus and Weissella. We showed that constituents in soybean wastewater can be converted to SCP through microbial community-based growth processes and demonstrated the effect of variable influent wastewater composition on SCP production.

Microbial community-based bacterial protein from soybean-processing wastewater as a value-added alternative fish feed ingredient for Asian sea bass (Lates calcarifer)

“…They were also formulated to provide essential amino acids to fish; however, at 18% and 14% in the FM control diet and 50SCP experimental diet, respectively, lysine was below the required level (Table 2). The remaining essential amino acid requirements were met, in agreement with a recent study by Vethathirri et al (2022) where microbial . CC-BY-NC-ND 4.0 International license available under a (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity.…”

“…A microbial community-based approach to build SCP has several potential advantages over axenic culturing (Vethathirri et al, 2021), such as a higher protein content due to synergistic interactions between different SCP-producing microorganisms and the utilization of various carbon and nitrogen sources available in the substrate (Alloul et al, 2021a; Vethathirri et al, 2022), the accumulation of intracellular components (Li et al, 2022), and process stability in terms of resistance and resilience to disturbances (Santillan et al, 2020a; Santillan et al, 2020b; Santillan et al, 2021). The microbial composition of the microbial community-based SCP employed in the experimental diet was dominated by the genera Acidipropionibacterium and Propioniciclava (Figure 2), which have potential as probiotics and producers of valuable metabolites.…”

“…It has been shown that microbial community-based single SCP grown on wastewaters from potato and starch, brewery or dairy industries, meets several of the essential amino acid requirements of fish and shrimp (Vethathirri et al, 2021). However, FPWW of variable chemical composition may also lead to different mixed SCP communities (Vethathirri et al, 2022), thus more research is needed for a broader validation of this approach.…”

“…To produce microbial SCP, four 4-L bioreactors were operated as sequencing batch reactors (SBRs) on continuous 12-h cycles with intermittent aeration for 136 days. Reactors received wastewater from a soybean processing company in Singapore as described in Vethathirri et al (2022). Water temperature was maintained at 30 °C, and the sludge was continuously mixed at 375 rpm.…”

“…An alternative would be a whole-community approach for SCP production, leveraging the microorganisms already present in the wastewater (Vethathirri et al, 2021), but remains largely unexplored. A recent study showed that microbial community-based SCP produced directly from soybean processing wastewaters contained essential amino acids for fish as well as taxa with probiotic potential (Vethathirri et al, 2022). However, the feasibility of using such SCP as fish feed ingredient for aquaculture has yet to be established.…”