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Applied and Environmental Microbiology, July 2009, p. 4410-4418, Vol. 75, No. 13
0099-2240/09/$08.00+0     doi:10.1128/AEM.02354-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Aldouronate Utilization in Paenibacillus sp. Strain JDR-2: Physiological and Enzymatic Evidence for Coupling of Extracellular Depolymerization and Intracellular Metabolism {triangledown}

Guang Nong, John D. Rice, Virginia Chow, and James F. Preston*

Department of Microbiology and Cell Sciences, University of Florida, Gainesville, Florida 32611

Received 14 October 2008/ Accepted 19 April 2009

Paenibacillus sp. strain JDR-2, an aggressively xylanolytic bacterium isolated from decaying sweet gum wood, secretes a multimodular glycohydrolase family GH10 endoxylanase (XynA1) anchored to the cell surface. The gene encoding XynA1 is part of a xylan utilization regulon that includes an aldouronate utilization gene cluster with genes encoding a GH67 {alpha}-glucuronidase (AguA), a GH10 endoxylanase (XynA2), and a GH43 arabinofuranosidase/β-xylosidase (XynB). Here we show that this Paenibacillus sp. strain is able to utilize methylglucuronoxylose (MeGAX1), an aldobiuronate product that accumulates during acid pretreatment of lignocellulosic biomass, and methylglucuronoxylotriose (MeGAX3), the product of the extracellular XynA1 acting on methylglucuronoxylan (MeGAXn). The average rates of utilization of MeGAXn, MeGAX1, and MeGAX3 were 149.8, 59.4, and 54.3 µg xylose equivalents·ml–1·h–1, respectively, and were proportional to the specific growth rates on the substrates. AguA was active with MeGAX1 and MeGAX3, releasing 4-O-methyl-D-glucuronate {alpha}-1,2 linked to a nonreducing terminal xylose residue. XynA2 converted xylotriose, generated by the action of AguA on MeGAX3, to xylose and xylobiose. The ability to utilize MeGAX1 provides a novel metabolic potential for bioconversion of acid hydrolysates of lignocellulosics. The 2.8-fold-greater rate of utilization of polymeric MeGAXn than that of MeGAX3 indicates that there is coupling of extracellular depolymerization, assimilation, and intracellular metabolism, allowing utilization of lignocellulosics with minimal pretreatment. Along with adjacent genes encoding transcriptional regulators and ABC transporter proteins, the aguA and xynA2 genes in the cluster described above contribute to the efficient utilization of aldouronates derived from dilute acid and/or enzyme pretreatment protocols applied to the conversion of hemicellulose to biofuels and chemicals.

* Corresponding author. Mailing address: Department of Microbiology and Cell Science, University of Florida, Bldg. 981, Museum Rd., Gainesville, FL 32611-0700. Phone: (352) 392-5923. Fax: (352) 392-5922. E-mail: jpreston{at}ufl.edu

{triangledown} Published ahead of print on 24 April 2009.

Applied and Environmental Microbiology, July 2009, p. 4410-4418, Vol. 75, No. 13
0099-2240/09/$08.00+0     doi:10.1128/AEM.02354-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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