Isolation and Characterization of Levoglucosan-Metabolizing Bacteria

Bacteria were isolated from wastewater and soil containing charred wood remnants based on their ability to use levoglucosan as a sole carbon source and on their levoglucosan dehydrogenase (LGDH) activity. On the basis of their 16S rRNA gene sequences, these bacteria represented the diverse genera Microbacterium, Paenibacillus, Shinella, and Klebsiella. Genomic sequencing of the isolates verified that two isolates represented novel species, Paenibacillus athensensis MEC069^T and Shinella sumterensis MEC087^T, while the remaining isolates were closely related to Microbacterium lacusdiani or Klebsiella pneumoniae. The genetic sequence of LGDH, lgdA, was found in the genomes of these four isolates as well as Pseudarthrobacter phenanthrenivorans Sphe3. The identity of the P. phenanthrenivorans LGDH was experimentally verified following recombinant expression in Escherichia coli. Comparison of the putative genes surrounding lgdA in the isolate genomes indicated that several other gene products facilitate the bacterial catabolism of levoglucosan, including a putative sugar isomerase and several transport proteins. IMPORTANCE Levoglucosan is the most prevalent soluble carbohydrate remaining after high-temperature pyrolysis of lignocellulosic biomass, but it is not fermented by typical production microbes such as Escherichia coli and Saccharomyces cerevisiae. A few fungi metabolize levoglucosan via the enzyme levoglucosan kinase, while several bacteria metabolize levoglucosan via levoglucosan dehydrogenase. This study describes the isolation and characterization of four bacterial species that degrade levoglucosan. Each isolate is shown to contain several genes within an operon involved in levoglucosan degradation, furthering our understanding of bacteria that metabolize levoglucosan.