Trophic mode-dependent antibiotic sensitivity in the green microalgae Chlorella vulgaris and Chlamydomonas reinhardtii

Chlorella vulgaris and Chlamydomonas reinhardtii are widely used microalgae for various biotechnology applications. Antibiotics are routinely used during microalgal cultivation to prevent bacterial contamination or as selective markers during genome editing. As green microalgae contain both prokaryotic (70S) and eukaryotic (80S) ribosomes, ribosome-targeting antibiotics may exert trophic dependent effects. The response of these two common species to twelve commonly used antibiotics under photoautotrophic, mixotrophic, and heterotrophic conditions was investigated in liquid medium and agar-based medium. Minimum inhibitory concentrations (MICs) were determined by monitoring growth and varied substantially based on antibiotic class, trophic mode and medium format. Aminoglycosides which target both 70S and 80S ribosomes induced stronger inhibition than those targeting only 70S, with the weakest inhibition under mixotrophic conditions. Zeocin showed strong inhibition across all trophic modes but was less effective under heterotrophic conditions while rifampicin selectively inhibited C. reinhardtii under photoautotrophy. MICs of 70S ribosome targeting antibiotics were typically higher on agar for C. vulgaris , but not for C. reinhardtii , underscoring the greater resilience of C. vulgaris . These findings provide a comprehensive overview of antibiotic sensitivity in microalgae across both antibiotic mechanisms and trophic states, offering critical insights for optimizing selection strategies in genetic engineering, improving microalgal cultivation practices, and informing broader biotechnological applications. • MICs of 12 antibiotics across trophic modes were determined in Chlorella vulgaris and Chlamydomonas reinhardtii . • Antibiotic efficacy varied substantially across photoautotrophic, mixotrophic, and heterotrophic conditions. • Aminoglycosides targeting both 70S and 80S ribosomes caused stronger inhibition. • Agar cultures required higher antibiotic doses than liquid, especially in C. vulgaris .