Pantoea sp. P37 as a novel nonpathogenic host for the heterologous production of rhamnolipids.

Microbially derived surfactants, so-called biosurfactants, have attracted significant attention as an environmentally friendly alternative to their chemically synthesized counterparts. Particularly, rhamnolipids offer a large potential with their outstanding surfactant properties such as complete biodegradability, low toxicity, and stability. Rhamnolipids are naturally synthesized by the opportunistic human pathogen Pseudomonas aeruginosa under the tight regulation of a highly complex quorum-sensing system. The heterologous production of mono-rhamnolipids by a newly isolated nonpathogenic strain of the genus Pantoea was investigated. Analysis of the genome obtained by a chimeric assembly of Nanopore long reads and high-quality Illumina reads suggested that the strain has evolved to an epiphytic rather than a pathogenic lifestyle. Functional heterologous expression of the mono-rhamnolipid operon rhlAB derived from a P. aeruginosa strain was established and confirmed by HPLC analysis. Transcriptome analysis indicated destabilizing effects of the produced rhamnolipids on the cell envelope of the host resulting in the induction of molecular stress responses. After integration of the rmlBCDA operon, extracellular rhamnolipids in amounts up to 0.4 g/L could be detected and were identified as a mono-rhamnolipid Rha-C10 -C10 by MALDI-TOF mass spectrometry.