Interactive Effects of Ceftriaxone and Chitosan Immobilization on the Production of Arachidonic Acid by and the Microbiome of the Chlorophyte Lobosphaera sp. IPPAS C-2047

Pharmaceuticals including antibiotics are among hazardous micropollutants (HMP) of the environment. Incomplete degradation of the HMP leads to their persistence in water bodies causing a plethora of deleterious effects. Conventional wastewater treatment cannot remove HMP completely, and a promising alternative is comprised by biotechnologies based on microalgae. The use of immobilized microalgae in environmental biotechnology is advantageous since immobilized cultures allow recycling of the microalgal cells, support higher cell densities, and boost tolerance of microalgae to stresses including HMP. Here we report on a comparative study of HMP (exemplified by the antibiotic ceftriaxone) removal by suspended and chitosan-immobilized cells of Lobosphaera sp. IPPAS C-2047 unialgal culture. We also monitored the dynamics of photosynthetic pigments content and the physiological condition of the cells as reflected by the activity of their photosynthetic apparatus. Special attention was paid to the changes in the accumulation of valuable arachidonic acid (C20:4). In addition to this, we followed the changes in the culture microbiome induced the antibiotic exposure. Collectively, our results showed that both suspended and immobilized cultures took up ceftriaxone from the culture medium. In the case of immobilized culture, a significant amount of the antibiotic was adsorbed on the chitosan carrier itself. The dynamics of the taxonomic composition of the microbiome of the microalgae was more shifted by the immobilization on the chitosan than by exposure to 20 mg/L of ceftriaxone. The possibility and limitations of the using of chitosan-immobilized Lobosphaera sp. IPPAS C-2047 for HMP removal coupled with the production of valuable long-chain polyunsaturated fatty acids is discussed.