Cell aggregation and temperature regulation mitigate Poterioochromonas predation on fast-growing cyanobacteria

Cyanobacteria are promising for sustainable bioproduction but are vulnerable to predation, particularly by the mixotrophic protist Poterioochromonas, which threatens large-scale cultivation. This study investigates the predation susceptibility of three fast-growing cyanobacterial strains—Synechococcus elongatus UTEX 2973 (S2973), Synechococcus elongatus PCC 11801 (S11801), and Synechococcus sp. PCC 11901 (S11901)—to Poterioochromonas sp. CCMP 2740, using a reproducible predator-prey model. Grazing experiments, microscopy, and growth measurements revealed that while all strains were susceptible, S11801 and S11901 exhibited significantly higher resistance than S2973. This resistance was linked to their natural formation of microcolonies, which offered spatial protection and size exclusion against the predator. Engineering S2973 to aggregate enhanced its predation tolerance, confirming cell aggregation as a protective mechanism. Additionally, increasing temperature to 38 °C effectively eliminated the predator while supporting robust cyanobacterial growth, presenting a practical control strategy. These findings offer valuable insights for strain selection and predator management in cyanobacterial biomanufacturing, highlighting cell aggregation as an innate defense and temperature regulation as a practical control method.