Nitrogenous fertilizer‐free microalgal culture using nitrogen‐fixing cyanobacteria‐derived extracts for sustainable food production

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SUMMARYTo establish an efficient cultured meat production system, we developed a novel circular cell culture (CCC) system using microalgae (Alvikia littoralis NBRC 102761) cultured in an animal cell waste medium. To reduce the external nitrogenous fertilizer input in the A. littoralis culture, we grew microalgae in nitrogenous fertilizer‐free media with an extract of the nitrogen‐fixing cyanobacteria Anabaena sp. PCC 7120 and Scytonema sp. NIES‐2130. The increase in A. littoralis cell concentration in seawater containing Scytonema extracts was 4.4‐fold higher than that in nitrogenous fertilizer‐free artificial seawater; however, it was 0.8‐fold lower than that in fertilizer‐enriched seawater. However, with the Anabaena extract, the increase in A. littoralis cell concentration was 14.6‐fold higher than that in nitrogenous fertilizer‐free artificial seawater and 2.1‐fold higher in fertilizer‐enriched seawater. Anabaena extract contained larger amounts of ammonium (7.6‐fold) than Scytonema extract, which was considered to be linked to the efficient growth of A. littoralis. Alvikia littoralis consumed 97% of the ammonium in the Anabaena extract, demonstrating that microalgae proliferated using the nitrogen source of the extract. Amino acids were extracted 2.8 times more efficiently from A. littoralis cultured with Anabaena extract than from fertilizer‐enriched seawater. Moreover, the concentration of A. littoralis cells increased 12.6‐fold in the waste medium of animal cells and 19.0‐fold in the waste medium with the Anabaena extract, indicating that the addition of the extract accelerated the growth of A. littoralis. The amount of ammonium increased in the waste culture medium with addition of Anabaena extract, and A. littoralis consumed 99% of the ammonium from the waste medium containing the extract. This microalgal culture method using Anabaena extract further improves the CCC system and could contribute to the establishment of a sustainable cultured meat production system that reduces the use of chemical fertilizers, crops and livestock, and also effectively uses waste.