Nutritional value and production of three species of purple non‐sulphur bacteria grown in palm oil mill effluent and their application in rotifer culture

Three species of purple non‐sulphur bacteria (PB), Rhodopseudomonas palustris, Rhodobacter sphaeroides and Rhodovulum sulfidophilum, grown in palm oil mill effluent (POME) were successfully used for the first time as feed for rotifers (Brachionus rotundiformis). Rp. palustris cultured in both POME and synthetic medium gave the highest rotifer density (332–395 individuals mL⁻¹) from 3 to 5 days at 10 g L⁻¹ salinity. Other PB cultured in synthetic medium generally support higher rotifer density than PB cultured in POME. Rb. sphaeroides had the highest biomass (1.91–3.34 g L⁻¹) and growth rate (0.64–1.11 g day⁻¹) in both types of culture medium. Nevertheless, only Rv. sulfidophilum grown in POME contained both eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), indicating its ability to biosynthesize them from POME nutrients. Rotifers fed Rv. sulfidophilum grown in POME had significantly higher amounts of protein, arachidonic acid, EPA and DHA than rotifers fed Rv. sulfidophilum grown in synthetic medium. The nutritional profile of lipid‐deficient PB can be improved by growing them in POME, and these enriched PB produced at an estimated cost of USD 8.71–35.35 kg⁻¹ dry biomass, depending on species, can support rotifer production in a batch culture system.