Abstract
Extensive research has been done on examining the autotrophic growth of Acetobacterium woodii with gaseous substrates (hydrogen and carbon dioxide) to produce acetic acid. However, only limited work has been performed on the heterotrophic growth of A. woodii using pure sugars or lignocellulosic feedstocks-derived sugars as substrates. In this study, we examine the growth kinetics and acetic acid production of A. woodii on glucose and xylose. While good growth was observed with glucose as substrate, no significant growth was obtained on xylose. Kinetic studies were performed in batch culture using different concentrations of glucose, ranging from 5 g/L to 40 g/L. The highest acetate production of 6.919 g/L with a product yield of 0.76 g acetic acid/g glucose was observed with 10 g/L glucose as initial substrate concentration. When testing A. woodii on corn stover hydrolysate (CSH) and wheat straw hydrolysate (WSH) formed after pretreatment and enzymatic hydrolysis, we found that A. woodii showed acetic acid production of 7.64 g/L and a product yield of 0.70 g acetic acid/g of glucose on WSH, while the acetic acid production was 7.83 g/L with a product yield of 0.65 g acetic acid/g of glucose on CSH. These results clearly demonstrate that A. woodii performed similarly on pure substrates and hydrolysates, and that the processes were not inhibited by the heterogenous components present in the lignocellulosic feedstock hydrolysates.
Highlights
Acetic acid is one of the most valuable, industrially important chemicals, with a global demand of 13 million tons of virgin acetic acid in the year 2015, which is forecasted to increase to approximately18 million tons by 2020
We explore the heterotrophic mode of growth by A. woodii, where ATP synthesis occurs by substrate level phosphorylation (SLP) of carbohydrates and other organic substrates, which are incompletely oxidized to produce acetate as the major end product
We study growth and product kinetics of A. woodii on two pure sugar substrates, glucose and xylose, which are the two major sugars present in lignocellulosic feedstocks, and further apply these results to study the production of acetic acid by A. woodii on two different pretreated and enzymatically hydrolyzed lignocellulosic substrates, wheat straw hydrolysate (WSH) and corn stover hydrolysate (CSH)
Summary
Acetic acid is one of the most valuable, industrially important chemicals, with a global demand of 13 million tons of virgin acetic acid in the year 2015, which is forecasted to increase to approximately18 million tons by 2020. Other commonly applied approaches of acetic acid production include aerobic fermentation of substrates like ethanol using Acetobacterium species, where ethanol is converted to acetic acid with oxygen, mainly using two types of fermentation processes, a trickling process or a submerged fermentation [6]. These processes suffer from high production cost due to the Fermentation 2019, 5, 17; doi:10.3390/fermentation5010017 www.mdpi.com/journal/fermentation
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