Paenibacillus lacisoli sp. nov., a mesotrione-degrading strain isolated from lakeside soil.

A Gram-stain-positive, facultatively anaerobic, rod-shaped bacterium, designated JX-17T, was isolated from a soil sample collected in Jiangxi Province, PR China. Growth was observed at 15-48 °C (optimum 37 °C), at pH 5.0-9.0 (optimum pH 7.0) and with 0-6.0% (w/v) NaCl (optimum 1.0%). Strain JX-17T could degrade approximately 50% of 50 mg/L mesotrione within 2 days of incubation, but could not use mesotrione as sole carbon source for growth. Strain JX-17T showed less than 95.3% 16S rRNA gene sequence similarity with type strains of the genus Paenibacillus. In the phylogenetic tree based on 16S rRNA gene and genome sequences, strain JX-17T formed a distinct lineage within the genus Paenibacillus. The ANI values between JX-17T and the most closely related type strains P. lentus CMG1240T and P. farraposensis UY79T were 70.1% and 71.4%, respectively, and the dDDH values between them were 19.0% and 23.3%, respectively. The major cellular fatty acids were anteiso-C15:0, iso-C16:0, anteiso-C17:0 and C16:0, the predominant respiratory quinone was MK-7, the major polar lipids were diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol, an unidentified glycolipid, an aminophospholipid and a phosphatidylinositol. The diagnostic diamino acid of the peptidoglycan was meso-diaminopimelic acid, and the DNA G + C content was 50.1 mol%. Based on the phylogenetic, phenotypic and chemotaxonomic characteristics, strain JX-17T represents a novel species within the genus Paenibacillus, for which the name Paenibacillus lacisoli sp. nov is proposed, with strain JX-17T (= GDMCC 1.3962T = KCTC 43568T) as the type strain.

A FadR-Type Regulator Activates the Biodegradation of Polycyclic Aromatic Hydrocarbons by Mediating Quorum Sensing in Croceicoccus naphthovorans Strain PQ-2.

Bacteria employ multiple transcriptional regulators to orchestrate cellular responses to adapt to constantly varying environments. The bacterial biodegradation of polycyclic aromatic hydrocarbons (PAHs) has been extensively described, and yet, the PAH-related transcriptional regulators remain elusive. In this report, we identified an FadR-type transcriptional regulator that controls phenanthrene biodegradation in Croceicoccus naphthovorans strain PQ-2. The expression of fadR in C. naphthovorans PQ-2 was induced by phenanthrene, and its deletion significantly impaired both the biodegradation of phenanthrene and the synthesis of acyl-homoserine lactones (AHLs). In the fadR deletion strain, the biodegradation of phenanthrene could be recovered by supplying either AHLs or fatty acids. Notably, FadR simultaneously activated the fatty acid biosynthesis pathway and repressed the fatty acid degradation pathway. As intracellular AHLs are synthesized with fatty acids as substrates, boosting the fatty acid supply could enhance AHL synthesis. Collectively, these findings demonstrate that FadR in C. naphthovorans PQ-2 positively regulates PAH biodegradation by controlling the formation of AHLs, which is mediated by the metabolism of fatty acids. IMPORTANCE Master transcriptional regulation of carbon catabolites is extremely important for the survival of bacteria that face changes in carbon sources. Polycyclic aromatic hydrocarbons (PAHs) can be utilized as carbon sources by some bacteria. FadR is a well-known transcriptional regulator involved in fatty acid metabolism; however, the connection between FadR regulation and PAH utilization in bacteria remains unknown. This study revealed that a FadR-type regulator in Croceicoccus naphthovorans PQ-2 stimulated PAH biodegradation by controlling the biosynthesis of the acyl-homoserine lactone quorum-sensing signals that belong to fatty acid-derived compounds. These results provide a unique perspective for understanding bacterial adaptation to PAH-containing environments.

The LuxI/LuxR-Type Quorum Sensing System Regulates Degradation of Polycyclic Aromatic Hydrocarbons via Two Mechanisms.

Members of the Sphingomonadales are renowned for their ability to degrade polycyclic aromatic hydrocarbons (PAHs). However, little is known about the regulatory mechanisms of the degradative pathway. Using cross-feeding bioassay, a functional LuxI/LuxR-type acyl-homoserine lactone (AHL)-mediated quorum sensing (QS) system was identified from Croceicoccus naphthovorans PQ-2, a member of the order Sphingomonadales. Inactivation of the QS system resulted in a significant decrease in PAHs degradation. The QS system positively controlled the expression of three PAH-degrading genes (ahdA1e, xylE and xylG) and a regulatory gene ardR, which are located on the large plasmid. Interestingly, the transcription levels of these three PAH-degrading genes were significantly down-regulated in the ardR mutant. In addition, bacterial cell surface hydrophobicity and cell morphology were altered in the QS-deficient mutant. Therefore, the QS system in strain PQ-2 positively regulates PAH degradation via two mechanisms: (i) by induction of PAH-degrading genes directly and/or indirectly; and (ii) by an increase of bacterial cell surface hydrophobicity. The findings of this study improve our understanding of how the QS system influences the degradation of PAHs, therefore facilitating the development of new strategies for the bioremediation of PAHs.