INFLUENCE OF VITAMIN B12 ON MIXOTROPHIC GROWTH: INTERACTIONS BETWEEN EUGLENA GRACILIS AND MESORHIZOBIUM LOTI

Mixotrophic protists, capable of utilizing both photosynthetic and heterotrophic pathways for energy,are particularly important in high DOC lakes, i.e., lakes with high concentration of dissolved organic carbon. We studied the growth responses and biochemical traits of a freshwater mixotrophic protist Euglena gracilis in different culture conditions. We were specifically interested in its relationship with Mesorhizobium loti, a bacterium that synthetizes among other essential vitamin B12 (cobalamin). E. gracilis is a vitamin B12 auxotroph, i.e., it requires vitamin B12 for growth albeit it cannot synthesize this vitamin . We co-cultured E. gracilis and M. loti in autotrophic conditions and adjusted the concentrations of DOC, nitrogen and B12 to study their combined impact on the growth and nutritional quality,specifically polyunsaturated fatty acids (PUFA) and proteins of  E. gracilis. The addition of external carbon benefited both partners possibly due to the phagocytic behaviour of E. gracilis . Additionally, co culture with bacteria significantly increased total fatty acids content in algae, including essential PUFAs:eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Co-deprivation of nitrogen and B12 adversely affected algal growth and protein content, yet the algae was more resilient under combined stress than with B12 deprivation alone. These findings emphasize the importance of vitamin B12 availability and the relationship with v itamin B12 producing bacteria on the growth and biochemical traits of mixotrophic protists, which, in turn, have cascading effects on aquatic food webs, particularly regarding their nutritional quality.

Presentation Preference: Either

Primary Presenter: Sadikshya Ghimire, University of Eastern Finland (sadikshya.ghimire@uef.fi)

Authors:

Sadikshya Ghimire, University of Eastern Finland  (sadikshya.ghimire@uef.fi)

Mohammad Salar Sohrabi, University of Eastern Finland  (salar.sohrabi@uef.fi)

Xuan Zhou, University of Eastern Finland  (xuan.zhou@uef.fi)

Ursula Strandberg, University of Eastern Finland  (ursula.strandberg@uef.fi)