Bioprospecting of wild type ethanologenic yeast for ethanol fuel production from wastewater-grown microalgae

Abstract

Background: Wild-type yeasts have been successfully used to obtain food products, yet their full potential as fermenting microorganisms for large-scale ethanol fuel production has to be determined. In this study, wild-type ethanologenic yeasts isolated from a secondary effluent were assessed for their capability to ferment saccharified microalgae sugars.

Results: Yeast species in wastewater were identified sequencing the Internal Transcribed Spacers 1 and 2 regions of the ribosomal cluster. Concurrently, microalgae biomass sugars were saccharified via acid hydrolysis, producing 5.0 ± 0.3 g L^-1 of fermentable sugars. Glucose consumption and ethanol production of yeasts in hydrolyzed-microalgae liquor were tested at different initial sugar concentrations and fermentation time. The predominant ethanologenic yeast species was identified as Candida sp., and glucose consumption for this strain and S. cerevisiae achieved 75% and 87% of the initial concentration at optimal conditions, respectively. Relatively similar ethanol yields were determined for both species, achieving 0.45 ± 0.05 (S. cerevisiae) and 0.46 ± 0.05 g ethanol per g glucose (Candida sp.).

Conclusion: Overall, the results provide a first insight of the fermentation capacities of specific wild-type Candida species, and their potential role in ethanol industries seeking to improve their cost-efficiency.

Keywords: Candida sp.; Fermentation; Hydrolysis; Microalgae; Municipal wastewater; Scenedesmus sp.

Fig. 1

Morphological analysis of Candida sp. (a, b) and Pichia sp. (c, d) using a stereoscopic microscope

Fig. 2

Glucose consumption and ethanol production for yeast isolates. Candida sp.: a 25 g L⁻¹ dextrose-enriched filtered wastewater; b 45 g L⁻¹ dextrose-enriched filtered wastewater. Pichia sp.: c 25 g L⁻¹ dextrose-enriched filtered wastewater; d 45 g L⁻¹ dextrose-enriched filtered wastewater. No replicates

Fig. 3

Glucose consumption and ethanol production during microalgal hydrolysate fermentation. a Saccharomyces cerevisiae S288C and b Candida sp

Fig. 4

Effect of response variables during microalgal hydrolysate fermentation. Saccharomyces cerevisiae S288C: a Glucose consumption; b ethanol production. Candida sp.: c Glucose consumption; d ethanol production