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Kluyveromyces marxianus and Bacillus coagulans co-cultivation: Efficient co-production of bioethanol and lactic acid from pomegranate peels

2024    Demiray, Ekin; Gonzalez-Fernandez, Cristina; Tomas-Pejo, Elia

Lignocellulosic biomass utilization is challenging due to the presence of several carbon sources. Thus, microorganisms with different sugar preferences can be used in co-cultures to overcome this hurdle. This work addressed the simultaneous production of lactic acid (LA) from C5 sugars (i.e., xylose) and bioethanol from C6 (i. e., glucose/fructose) with Bacillus coagulans and Kluyveromyces marxianus, respectively. Sequential inoculation and co-inoculation of microorganisms were also compared. At pH 6, co-inoculation in synthetic media resulted in higher bioethanol (0.51 g/g) and LA (0.98 g/g) yields than sequential inoculation. Furthermore, when using lignocellulosic hydrolysates obtained after enzymatic hydrolysis of 20 % w/w pomegranate peels (PP), 92 % and 98 % of the theoretical maximum bioethanol and LA, respectively, were obtained. This study demonstrated the efficient bioethanol/LA co-generation despite the different optimum fermentation conditions of microorganisms and will pave the way to consider co-cultures for improving process efficiency in lignocellulosic biorefineries.