Transcriptomic profiling reveals the molecular responses of Rhodococcus aetherivorans DMU1 to skatole stress

Advances in microbial degradation of skatole: A review

In recent years, foul odors have led to widespread public complaints and have become a prominent issue in the field of environmental protection. Skatole, as one of the important components of foul odors, is a decomposition product of tryptophan in the intestines of animals and is mainly found in animal feces. Skatole not only has significant pulmonary toxicity to animals but also poses potential carcinogenic risks to humans. The biological method of removing skatole has the notable advantages of being cost-effective, efficient, and environmentally friendly. However, current research on the microbial degradation of skatole is still insufficient, the metabolic pathways for microbial degradation of skatole are not yet fully elucidated, and there is a lack of research on the functional genes involved in degradation. This review outlines skatole's production and distribution in solid, liquid, and gas media, identifies microorganisms capable of skatole degradation, and examines the microbial degradation mechanisms and influencing factors. Additionally, we summarize the hydroxyindole oxidative ring-opening pathway for skatole degradation in anaerobic conditions and multiple aerobic pathways, including oxidative ring-opening and ring-cleaving. Catechol 1,2-dioxygenase is proposed as a key enzyme in the downstream metabolism of microbial skatole degradation, offering guidance for future research.

Unraveling the signaling roles of indole in an opportunistic pathogen Pseudomonas aeruginosa strain Jade-X

Pseudomonas aeruginosa, which can produce several toxins and form biofilm, is listed among the priority pathogens. Indole is a ubiquitous aromatic pollutant and signaling molecule produced by tryptophanase in bacteria. Herein, the impacts of indole on a newly isolated P. aeruginosa strain Jade-X were systematically investigated. Indole (0.5-2.0 mM) enhanced the biofilm production by 1.33-2.31-fold after 24 h incubation at 30 °C. However, the effects indole on biofilm formation were intricate and closely intertwined with factors such as incubation temperature, bacterial growth stage, and indole concentration. The twitching motility was enhanced by 1.15-1.99-fold by indole, potentially facilitating surface exploration and biofilm development. Indole reduced the production of virulence factors (pyocyanin and pyoverdine) as well as altered the surface properties (zeta potential and hydrophobicity). Transcriptional analysis revealed that indole (1.0 mM) significantly downregulated mexGHI-opmD efflux genes (4.73-6.91-fold) and virulence-related genes (pqs, pch, and pvd clusters, and flagella-related genes), while upregulating pili-related genes in strain Jade-X. The quorum sensing related signal regulators, including RhlR, LasR, and MvfR (PqsR), were not altered by indole, while other six transcriptional regulators (AmrZ, BfmR, PchR, QscR, SoxR, and SphR) were significantly affected, implying that indole effects might be regulated in a complex and delicate manner. This study should provide new insights into our understanding of indole signaling roles.