Abstract
AbstractLignocellulosic biomass is the most abundant bioresource on earth containing polymers mainly consisting of d‐glucose, d‐xylose, l‐arabinose, and further sugars. In order to establish this alternative feedstock apart from applications in food, we engineered Pseudomonas putida KT2440 as microbial biocatalyst for the utilization of xylose and arabinose in addition to glucose as sole carbon sources. The d‐xylose‐metabolizing strain P. putida KT2440_xylAB and l‐arabinose‐metabolizing strain P. putida KT2440_araBAD were constructed by introducing respective operons from Escherichia coli. Surprisingly, we found out that both recombinant strains were able to grow on xylose as well as arabinose with high cell densities and growth rates comparable to glucose. In addition, the growth characteristics on various mixtures of glucose, xylose, and arabinose were investigated, which demonstrated the efficient co‐utilization of hexose and pentose sugars. Finally, the possibility of using lignocellulose hydrolysate as substrate for the two recombinant strains was verified. The recombinant P. putida KT2440 strains presented here as flexible microbial biocatalysts to convert lignocellulosic sugars will undoubtedly contribute to the economic feasibility of the production of valuable compounds derived from renewable feedstock.
Highlights
The development of alternative feedstocks as carbon sources for the industrial biotechnology is one of the major goals to achieve cost‐effective and economically efficient bioprocesses, since the price for raw materials especially those of the carbon sources represents a significant proportion of total production costs
In contrast to the wild‐type and the P. putida strain containing the empty vector, this strain was able to grow on xylose and reached an optical density at 600 nm (OD600) of 9.8, what is similar to its growth on glucose (OD600 = 9.4)
A decreasing concentration of xylose could be observed during the cultivation, which is most likely caused by the activity of glucose dehydrogenase (Gcd)
Summary
The development of alternative feedstocks as carbon sources for the industrial biotechnology is one of the major goals to achieve cost‐effective and economically efficient bioprocesses, since the price for raw materials especially those of the carbon sources represents a significant proportion of total production costs. While cellulose is primarily used for other industrial applications, 60 billion tons of hemicelluloses remain almost completely unused every year, which can be hydrolyzed into sugar containing hydrolysates by chemical or enzymatic hydrolysis This is a prerequisite to use them as substrates for bioprocesses, since typically used microorganisms in industrial biotechnology are naturally unable to use polymers directly (Sun & Cheng, 2002; Xu, Sun, Liu, & Sun, 2006). For the utilization of l‐arabinose, a group of three genes, araB (ribulokinase), araA (l‐arabinose isomerase), and araD (l‐ribulose phosphate 4‐epimerase), is necessary, which mediates the conversion of l‐arabinose though l‐ribulose and l‐ribulose 5‐phosphate to d‐xylulose 5‐phosphate (Deanda, Zhang, Eddy, & Picataggio, 1996; Xiong, Wang, & Chen, 2016) This araBAD operon has been successfully integrated and heterologously expressed in C. glutamicum (Kawaguchi, Sasaki, Vertès, Inui, & Yukawa, 2008) to enable its growth on l‐arabinose. The growth behaviors of engineered P. putida KT2440 strains were investigated in detail during cultivation experiments on glucose, xylose, or arabinose as sole carbon sources as well as on mixtures of these sugars and real hemicellulose hydrolysates, to investigate the potential of efficiently utilizing of this cost‐effective and renewable feedstock
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