Nonsterile Cultivation of the Thermophilic Cyanobacterium Parathermosynechococcus lividus PCC 6715 in a Floating Light Ball Reactor (FLBR) on 53‐L Scale for Zeaxanthin Production

ABSTRACT In this study, we demonstrate the successful cultivation of the thermophilic cyanobacterium Parathermosynechococcus lividus PCC 6715 at up to 53‐L scale in a Floating Light Ball Reactor (FLBR) with β ‐carotenoid zeaxanthin levels of 1.4–2.0 mg g − 1 using high‐performance liquid chromatography (HPLC) and United States Pharmacopeia (USP) reference standards. The Floating Light Ball Reactor, recently developed in our group, is a photobioreactor system for microalgae and cyanobacteria cultivation that employs submerged light balls, enabling cultivation in existing containers. To address key constraints in the economic scale‐up of microalgae and cyanobacteria cultivation, 24 h continuous cultivation of extremophiles was investigated under artificial internal illumination and non‐sterile conditions. Elevated temperatures (≥ 45°C) substantially reduce contamination risk and may therefore facilitate industrial implementation. In a P. lividus PCC 6715 culture at 55°C, the only predominant contaminant was Truepera radiovictrix detected at low abundance (<1%) by next‐generation sequencing, light microscopy, and scanning electron microscopy. This proof‐of‐concept study demonstrates that the FLBR system supports β ‐carotenoid production even under extremophilic conditions with 24 h internal illumination, providing a basis for subsequent economic scale‐up.