Microbial removal of acetate selectively from sugar mixtures

Abstract

Acetic acid is an unavoidable constituent of the biomass hydrolysates generated from acetylated hemicellulose and lignin, and acetate affects the performance of microbes used to convert these hydrolysates into biofuels or other biochemicals. In this study, acetate was selectively removed from synthetic mixtures of glucose and xylose using metabolically engineered Escherichia coli strains having mutations in the glucose phosphotransferase system (PTS) genes (ptsG, manZ, crr), glucokinase (glk), and xylose (xylA). In batch culture, ALS1060 (ptsG manZ glk xylA) consumed exclusively acetate to depletion, and then consumed the two sugars only at a very slow rate (a growth rate of about 0.01 h(-1)). We also examined the effects of an additional knockout of either malX, fruA, fruB, bglF, or crr, genes that are involved in other PTSs, and a batch process using KD840 (ptsG manZ glk crr xylA) demonstrated a further reduction in glucose or xylose consumption by E. coli. These results demonstrate the feasibility of using a substrate-selective approach for the pre-treatment of biomass hydrolysate for microbial processes.

Simultaneous utilization of glucose, xylose and arabinose in the presence of acetate by a consortium of Escherichia coli strains

“…In a previous study, E. coli MG1655 derivatives were used to remove acetate selectively from a mixture of acetate, xylose and glucose [18]. Here we extend those results, introduce arabinose into the sugar mixture, and also examine the consumption of the three sugars.…”

“…Interestingly, the C derivative ALS1392 used in the present study grew at a significantly greater growth rate on acetate than reported for the wild-type strain MG1655 (0.35 h -1 versus 0.22 h -1 ). Moreover, although slow sugar consumption by an acetate-selective strain of MG1655 was observed after acetate depletion [18], sugar consumption did not occur in the presence of acetate. In the current study we did not observe appreciable glucose consumption after 32 h. When it occurs, glucose degradation might occur as a result of a mutation or by the induction of an unknown gene.…”

“…One advantage demonstrated for this substrate-selective uptake is that the system can adapt to fluctuations in the feed stream; that is, culture populations change in concert with a variable feed composition, which was demonstrated for the conversion of a xylose and glucose mixture into lactic acid [17]. The same approach has been used to remove acetate selectively from sugars [18]. Presumably additional, targeted metabolic engineering strategies could be used to form other desired products independently from each of the strains making up the consortium.…”

Isolation and Characterization of Bacteria That Use Furans as the Sole Carbon Source

“…We have recently developed a biological method to selectively remove another common inhibitor, acetate, from lignocellulosic hydrolysates [42]. This strategy involves the use of microorganisms which can only metabolize the target inhibitor from a mixture which includes the desired carbohydrates.…”

Avaliação da tolerância das leveduras xilanolíticas isoladas da Antártica ao hidrolisado hemicelulósico de bagaço de cana de açúcar visando à utilização de pentoses

“…A quantidade de produtos inibidores formados durante o processo de pré-tratamento de um material lignocelulósico é variável, sendo observado que a sua formação depende da biomassa utilizada e das condições de pré-tratamento utilizadas no processo como a concentração do ácido, temperatura, o tempo e pressão (PALMQVIST; HAHN-HÄGERDAL, 2000b). O ácido acético é o único composto tóxico, cuja liberação não pode ser evitada, visto que o mesmo pertence à matriz lignocelulósica (LAKSHMANASWAMY et al, 2011). Desta forma, o consumo de ácido acético presente no hidrolisado é uma característica interessante para processos de bio-destoxificação, onde se busca o rápido consumo de ácido, com baixo consumo dos demais açúcares (LAKSHMANASWAMY et al, 2011;SCHNEIDER, 1996;SHAW et al, 2015).…”