Production of xylonic acid by Klebsiella pneumoniae

Abstract

The glucose oxidation pathway is important for glucose catabolism in Klebsiella pneumoniae. Gluconic acid and 2-ketogluconic acid are intermediates of this pathway, and the production of these two chemicals has been developed in K. pneumoniae mutants. Catalysis characteristic research in this study has shown that xylose is a suitable substrate of the glucose dehydrogenase of this pathway. Here, using xylose as substrate, xylonic acid was accumulated in the broth of K. pneumoniae culture, and this process was dependent upon acidic conditions. Using a mixture of glucose and xylose as substrates, a mixture of xylonic acid and gluconic acid was produced by the Δgad mutant of K. pneumoniae; gluconic acid was synthesized early, and xylonic acid synthesis began after most glucose was consumed. Using the hydrolysate of bamboo as substrate, mixture of 33 g/L gluconic acid and 14 g/L xylonic acid were produced by K. pneumoniae Δgad. In fed-batch fermentation, 103 g/L xylonic acid was produced after 79 h culture, with a conversion ratio of 1.11 g/g. This is the first report of xylonic acid produced by K. pneumoniae. Production of xylonic acid and gluconic acid using bamboo hydrolysate is a novel approach for biomass utilization.

Biotransformation of D-xylose to D-xylonic acid coupled to medium chain length polyhydroxyalkanoate production in cellobiose-grownPseudomonas putidaEM42

“…Periplasmic xylose conversion to xylonate was previously identified as a competing reaction for xylose assimilation by recombinant P. putida EM42 during a five-day cultivation experiment (Dvořák and de Lorenzo, 2018). Periplasmic glucose dehydrogenase was shown to be a crucial component for xylose oxidation in our strain as well as in several xylonate producing bacteria including Klebsiella pneumoniae and some other pseudomonads (Hardy et al , 1993; Meijnen et al , 2008; Köhler et al ., 2014; Wang et al , 2016; Dvořák and de Lorenzo, 2018). In P. putida KT2440, and correspondingly also in strain EM42, membrane-bound glucose dehydrogenase Gcd (PP1444) oxidises xylose to xylonolactone with pyrroloquinoline quinone (PQQ) as a cofactor.…”

“…This result indicates that the xylose oxidation in P. putida EM42 is not necessarily growth-dependent as reported with P. fragi (Buchert et al , 1986; Buchert and Viikari, 1988). It is worth to note that a number of studies on microbial xylonate production have reported the association of xylose oxidation to a host’s growth (Toivari et al , 2012; Köhler et al , 2014; Wang et al , 2016) but some have not. One example of the latter is recent work by Zhou and co-workers (2017) on G. oxydans , which could be used repeatedly for xylonate production in a bioreactor with an improved oxygen delivery system.…”

“…Similarly to other naturally occurring or recombinant xylonate producers (Nygård et al , 2011; M. Toivari et al , 2012; Wang et al , 2016; Zhou et al , 2017; Gao et al ., 2019) P. putida was grown in a medium rich in amino acids and vitamins, namely in LB (La Rosa et al ., 2016). However, such complex media are expensive and thus unsuitable for large-scale bioprocesses.…”

“…Rapid transformation of pentose into free xylonate with only minor accumulation of xylonolactone intermediate was observed. Such extracytoplasmic production and secretion are advantageous over intracellular xylose oxidation: cytoplasm acidification is avoided, the reaction of interest does not cross-interfere with the host’s metabolism, and xylonate can be purified directly from the culture medium (Wang et al , 2016).…”

“…Xylonate is naturally formed in the first step of oxidative metabolism of xylose by some archaea, bacteria, and fungi via the action of D-xylose or D-glucose dehydrogenases. Production of xylonate was reported for instance in Gluconobacter oxydans , in several Pseudomonas strains including P. fragi, P. taiwanensis or P. putida S12 , or in Klebsiella pneumoniae (Buchert et al, 1988; Meijnen et al ., 2009; Köhler et al ., 2015; Wang et al , 2016). Several other microorganisms including Escherichia coli or Saccharomyces cerevisiae were engineered for xylonate production from xylose (Nygård et al , 2011; Liu et al , 2012; M.…”