Enhanced production of biomass and lipids by Euglena gracilis via co-culturing with a microalga growth-promoting bacterium, Emticicia sp. EG3

Tadashi Toyama,Kengo Suzuki,Masaaki Morikawa,Yasuhiro Tanaka,Koji Yamada,Kazuhiro Mori,Tsubasa Hanaoka

doi:10.1186/s13068-019-1544-2

Tadashi Toyama, Kengo Suzuki + Show 5 more

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https://doi.org/10.1186/s13068-019-1544-2

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Abstract

BackgroundEuglena gracilis, a unicellular flagellated microalga, is regarded as one of the most promising species as microalgal feedstock for biofuels. Its lipids (mainly wax esters) are suitable for biodiesel and jet fuel. Culture of E. gracilis using wastewater effluent will improve the economics of E. gracilis biofuel production. Enhancement of the productivity of E. gracilis biomass is critical to creating a highly efficient biofuels production system. Certain bacteria have been found to promote microalgal growth by creating a favorable microenvironment. These bacteria have been characterized as microalgae growth-promoting bacteria (MGPB). Co-culture of microalgae with MGPB might offer an effective strategy to enhance microalgal biomass production in wastewater effluent culture systems. However, no MGPB has been identified to enhance the growth of E. gracilis. The objectives of this study were, therefore, to isolate and characterize the MGPB effective for E. gracilis and to demonstrate that the isolated MGPB indeed enhances the production of biomass and lipids by E. gracilis in wastewater effluent culture system.ResultsA bacterium, Emticicia sp. EG3, which is capable of promoting the growth of microalga E. gracilis, was isolated from an E. gracilis-municipal wastewater effluent culture. Biomass production rate of E. gracilis was enhanced 3.5-fold and 3.1-fold by EG3 in the co-culture system using a medium of heat-sterilized and non-sterilized wastewater effluent, respectively, compared to growth in the same effluent culture but without EG3. Two-step culture system was examined as follows: E. gracilis was cultured with or without EG3 in wastewater effluent in the first step and was further grown in wastewater effluent in the second step. Production yields of biomass and lipids by E. gracilis were enhanced 3.2-fold and 2.9-fold, respectively, in the second step of the system in which E. gracilis was co-cultured with EG3 in the first step.ConclusionEmticicia sp. EG3 is the first MGPB for E. gracilis. Growth-promoting bacteria such as EG3 will be promising agents for enhancing E. gracilis biomass/biofuel productivities.

Highlights

Euglena gracilis, a unicellular flagellated microalga, is regarded as one of the most promising species as microalgal feedstock for biofuels
EG3 for E. gracilis To test the hypothesis that indigenous bacteria in wastewater effluent could enhance the growth of E. gracilis, E. gracilis was grew in wastewater effluent with
The results suggested that microalgae growth-promoting bacteria (MGPB) were present in the E. gracilis-effluent culture with living indigenous bacteria

Summary

Introduction

A unicellular flagellated microalga, is regarded as one of the most promising species as microalgal feedstock for biofuels. Co-culture of microalgae with MGPB might offer an effective strategy to enhance microalgal biomass production in wastewater effluent culture systems. The objectives of this study were, to isolate and characterize the MGPB effective for E. gracilis and to demonstrate that the isolated MGPB enhances the production of biomass and lipids by E. gracilis in wastewater effluent culture system. E. gracilis can synthesize and accumulate a variety of valuable products such as wax esters [6], paramylon (β-1,3-glucan) [7], β-carotene, and vitamins C and E [8]. Wax esters—which consist mainly of C14:0 saturated fatty acid, myristic acid, C14:0 saturated fatty alcohols, and myristyl alcohols—are considered high-value biofuels [9, 10] These wax esters of E. gracilis are suitable for biodiesel and jet fuel [5, 10, 11]

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