Construction of engineered yeast producing ammonia from glutamine and soybean residues (okara)

Yukio Watanabe,Takeharu Nakahara,Kouichi Kuroda,Yuki Tatemichi,Wataru Aoki,Mitsuyoshi Ueda

doi:10.1186/s13568-020-01011-9

Abstract

Ammonia is an essential substance for agriculture and the chemical industry. The intracellular production of ammonia in yeast (Saccharomyces cerevisiae) by metabolic engineering is difficult because yeast strongly assimilates ammonia, and the knockout of genes enabling this assimilation is lethal. Therefore, we attempted to produce ammonia outside the yeast cells by displaying a glutaminase (YbaS) from Escherichia coli on the yeast cell surface. YbaS-displaying yeast successfully produced 3.34 g/L ammonia from 32.6 g/L glutamine (83.2% conversion rate), providing it at a higher yield than in previous studies. Next, using YbaS-displaying yeast, we also succeeded in producing ammonia from glutamine in soybean residues (okara) produced as food waste from tofu production. Therefore, ammonia production outside cells by displaying ammonia-lyase on the cell surface is a promising strategy for producing ammonia from food waste as a novel energy resource, thereby preventing food loss.

Highlights

Seventeen sustainable development goals (SDGs) have been proposed by the United Nations to solve global problems
To establish a biological technique for efficient ammonia production, it is necessary to avoid ammonia assimilation that occurs inside yeast cells
We displayed glutaminase, yeast cells by displaying a glutaminase (YbaS), on the yeast cell surface to produce ammonia from glutamine included in pretreated soybean residues outside the cells

Summary

Introduction

Seventeen sustainable development goals (SDGs) have been proposed by the United Nations to solve global problems. Two of these goals are aimed at producing affordable and clean energy to combat global warming (United Nations 2019). The development of technologies for sustainably producing energy and chemicals from biomass has become increasingly important (Lopes 2015; Wernick and Liao 2013). Ammonia is one of the most important chemicals for producing fertilizer and is essential for our daily lives. Ammonia is expected to act as a carrier of hydrogen (Lan et al 2012; Miura and Tezuka 2014) because it has high hydrogen content (17.6%), no carbon, and high mass density.

Methods

Results

Conclusion