Screening fungal partners for enhancing the vitality of a xenic algal culture via photosynthetic efficiency.

The xenic strain Chlorella sorokiniana was grown together with selected fungal strains to investigate the effect of fungi on the algal photosynthetic performance during cultivation. The introduction of well-selected fungal strains can potentially increase algal cultivation efficiency. The bacteria that inhabited the algae were identified and the coexistence of the fungi with the algae and bacteria in liquid and solid media was examined. Chlorophyll a fluorescence measurement, a commonly used method for determining the efficiency of plant photosynthesis under stressful conditions, was used to assess the condition of the algae. The algae were cultivated for eight weeks without supplementing the nutrient solution. The experiments showed that the fungal strains Clonostachys rosea, Rhodotorula mucilaginosa and Mortierella alpina formed stable interactions with the microalga C. sorokiniana and the bacteria in the microalgal culture. The time of the measurement and treatments caused changes in the fluorescence curve patterns. Differences in the profiles of the curves in different phases revealed modifications in the operation of the light-dependent photochemical reactions. Generally, the most positive changes in the chlorophyll a fluorescence induction curves (OJIP) were recorded in the double inoculation of C. sorokiniana with R. mucilaginosa + M. alpina and R. mucilaginosa + C. rosea. The results show that selected combinations of fungal strains can be a tool to improve the photosynthetic efficiency of C. sorokiniana.