Effect of mixed culture of yeast and microalgae on acetyl-CoA carboxylase and Glycerol-3-phosphate acyltransferase expression

https://doi.org/10.1016/j.jbiosc.2020.11.006Get rights and content

In recent years, some studies have reported that co-culturing green algae and yeast improve lipid and biomass concentration. In this study, a co-culture of the oleaginous yeast Rhodotorula glutinis and the microalgae Chlorella vulgaris was consequently conducted with inoculation of microalga and yeast in growth and stationary phases, respectively. For the first time, the expression of two pivotal enzymes in fatty acids synthetic pathway, acetyl-CoA carboxylase and Glycerol-3-phosphate acyltransferase, was evaluated. To evaluate the synergistic impacts of the mixed culture on the enzymes expression, several co-culture models were designed, including the use of different ratio of microalgae to yeast or the use of residual cell-free medium of yeast; a positive impact on enzymes overexpression was shown in the case of the co-culture of the two microorganisms, and when the remaining cell-free medium of yeast was added to the microalgal culture. The results of in vitro co-culture demonstrated increased 6- and 5-fold of nervonic acid (C24:1) and behenic acid (C22:0) concentrations, respectively, in 2:1 microalgae to yeast co-culture as compared to the monoculture batches. Addition of yeast residual cell-free medium in the 2:1 ratio to the microalgal culture enhanced 9 and 6 times nervonic acid (C24:1) and behenic acid (C22:0) amounts, respectively.

Section snippets

Materials

All chemicals used in this study were purchased from Merck (Darmstadt, Germany). The RNA extract kit was obtained from Denazist Asia (Mashhad, Iran). All solutions, prepared with double-distilled water, were kept at 4 °C before further use.

Cultivation of microorganisms and biomass processing

The yeast R. glutinis and the microalgae C. vulgaris used in this study were obtained from the Iranian Biological Resource Center (Tehran, Iran). R. glutinis was maintained on the agar slant of yeast and malt extract (YM) medium. The YM medium contained

Biomass production in pure culture versus co-culture

As C. vulgaris grew slower than R. glutinis, when the mixed culture was prepared from the logarithmic phases of the two species monoculture, the yeast was the prevailing species at the beginning of the co-culture, leading to reduction of the dissolved oxygen in the medium and hence causing anaerobic respiration. Yeast anaerobic respiration produces a large number of volatile organic acids decreasing the environmental pH as the significant factors in fatty acids profile of oleaginous

Acknowledgments

The authors would like to express their gratitude to Ms. Teimorim, the Life Science Engineering Laboratory staff, for her assistance in PCR experiments. The authors declare no conflict of interest.

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