# Genomic and proteomic characterization of a newly isolated Paenarthrobacter ilicis strain and its plasmid-mediated xanthan degradation

## TL;DR

A new strain of Paenarthrobacter ilicis was found to degrade xanthan, with its genome and proteome analyzed to reveal a plasmid-linked xanthan degradation pathway.

## Contribution

The discovery of a xanthan degradation region on a plasmid in Paenarthrobacter ilicis, potentially enabling horizontal gene transfer.

## Key findings

- The Paenarthrobacter ilicis strain 6C can degrade xanthan, a first in its genus.
- A xanthan degradation region was identified on a plasmid downstream from a mobilization gene.
- Proteome analysis revealed key enzymes and transporters involved in xanthan utilization.

## Abstract

Environmental soil samples enriched with xanthan gum led to the discovery and isolation of a novel strain of motile Paenarthrobacter ilicis in Bielefeld, Germany, which possesses a previously uncharacterized xanthan utilization gene region on its sole plasmid. This bacterium is the first member of the Paenarthrobacter genus to feature the ability to degrade xanthan. Growth experiments elucidated the optimal growth conditions with regard to pH (7.0) and temperature (28°C–30°C). The genome of Paenarthrobacter ilicis strain 6C consists of two replicons, namely a chromosome with 4,049,144 nucleotides (62.8% GC content) and a plasmid of 147,742 base pairs (61.8% GC content). This novel Paenarthrobacter ilicis strain carries 3,806 predicted coding regions, approximately half (51%) of which were verified with proteome analysis. Cultures grown with either glucose or xanthan as a carbon source were compared in relation to protein abundances at four growth stages and time points with regard to both intracellular and extracellular protein fractions. The proteome analysis (data are available via ProteomeXchange with identifier PXD063987) was undertaken using an LC-ESI-MS-MS shotgun proteomics approach, and the proteins were identified and quantified via label-free quantification using MaxQuant 2.6.6. This proteomics investigation exposed significant differences in protein abundances with regard to time and condition. Among the most highly enriched proteins seen when feeding exclusively on xanthan as a carbon source were enzymes encoded on a xanthan degradation plasmid (pPANIL_6C) with a xanthan utilization region coding for the PL8 xanthan lyase, GH38-, GH3-, GH9-family proteins, and several sugar transporters. These proteins constitute key components of a prospective xanthan degradation pathway.

A novel Paenarthrobacter isolate was sequenced and characterized by proteome analysis to provide the first clear look at a novel genus in the realm of xanthan-degrading microorganisms. This research provides additional groundwork for the ongoing characterization of Paenarthrobacter, as well as widening the understanding of xanthan-degrading microorganisms. For the first time, a xanthan degradation region was identified on a plasmid 1 kb directly downstream from a mobilization gene (mobF), posing the question of whether this metabolic capacity can be shared through horizontal gene transfer. Overall, this research expands the current knowledge base regarding Paenarthrobacter biology, as well as microbial xanthan degradation and utilization.