Evaluation of small organic acids present in fast pyrolysis bio‐oil from lignocellulose as feedstocks for bacterial bioconversion

Abstract

Small organic acids derived from fast pyrolysis of lignocellulosic biomass represent a significant proportion of microbially accessible carbon in bio‐oil. However, using bio‐oil for microbial cultivation is a highly challenging task due to its strong adverse effects on microbial growth as well as its complex composition. In this study, the main small organic acids present in bio‐oil as acetate, formate and propionate were evaluated with respect to their suitability as feedstocks for bacterial growth. For this purpose, the growth behavior of four biotechnological production hosts—Escherichia coli, Pseudomonas putida, Bacillus subtilis, and Corynebacterium glutamicum—was quantified and compared. The bacteria were cultivated on single acids and mixtures of acids in different concentrations and evaluated using common biotechnological efficiency parameters. In addition, cultivation experiments on pretreated fast pyrolysis‐derived bio‐oil fractions were performed with respect to the suitability of the bacterial strains to tolerate inhibitory substances. Results suggest that both P. putida and C. glutamicum metabolize acetate—the major small organic acid generated during fast pyrolysis of lignocellulosic biomass—as sole carbon source over a wide concentration range, are able to grow on mixtures of small organic acids present in bio‐oil and can, to a limited extent, tolerate the highly toxic inhibitory substances within bio‐oil. This work provides an important step in search of suitable bacterial strains for bioconversion of lignocellulosic‐based feedstocks and thus contributes to establishing efficient bioprocesses within a future bioeconomy.

Detoxification of a pyrolytic aqueous condensate from wheat straw for utilization as substrate in Aspergillus oryzae DSM 1863 cultivations

“…A multitude of procedures have already been described for the elimination of potential inhibitors from aqueous pyrolysis products and hydrolysates. Among them, the most common ones are extractions [ 11 , 21 ], adsorption processes using activated carbon [ 22 – 25 ] or other adsorbents [ 26 ], ion exchange [ 27 ] as well as overliming [ 28 – 30 ] and rotary evaporation [ 10 ]. In addition to these physical and chemical methods, biological treatments using whole cells [ 31 , 32 ] or enzymes [ 33 ] can also be applied to reduce the toxicity of liquid pyrolysis products.…”

Potential of biotechnological conversion of lignocellulose hydrolyzates by Pseudomonas putida KT2440 as a model organism for a bio‐based economy

“…Acetic acid had no negative influence on the growth of the two P. putida KT2440 strains (Figure b) until the highest applied acid concentration of 10 g/L. Furthermore, the strains metabolized acetic acid and partially used it for growth (Arnold, Tews, Tews, Kiefer, Henkel, & Hausmann, ). In detail, compared to cultivation without acetic acid (maximum OD 600 = 12.4), the wild type reached a maximum OD 600 of 14.6 and 15.1 at acetic acid concentrations of 2.5 and 10 g/L, respectively.…”

Metabolic history and metabolic fitness as drivers of anabolic heterogeneity in isogenic microbial populations

“…On the other hand, benzoate metabolism is regulated by downstream metabolites in both Pseudomonas and Thauera (Boll and Fuchs, 1995; Schühle et al ., 2003; Sudarsan et al ., 2016). Most relevant, acetate is not an optimal growth substrate for Pseudomonads (Hintermayer and Weuster‐Botz, 2017; Arnold et al ., 2019). It has been formerly shown that growth of P .…”

“…It has been formerly shown that growth of P . putida is inhibited by high acetate concentrations; documented mechanisms include interference with amino acid biosynthesis, and alterations of ion and osmotic balance (Fieschko and Humphrey, 1985; Roe et al ., 1998; Roe et al ., 2002; Arnold et al ., 2019). This could explain the relatively high number of inactive cells observed in the assay of P .…”