Novel indole-mediated potassium ion import system confers a survival advantage to the Xanthomonadaceae family

Nitrogen addition enhanced Per-fluoroalkyl substances' microbial availability in a wheat soil ecosystem

Per-fluoroalkyl substances (PFASs) have been widely detected in farmland soils and are understood to pose toxicological threats to soil microbiomes and crop safety. Meanwhile, farmland ecosystems have experienced increasing nitrogen loading caused by soil fertilization. Yet it is still unclear how nitrogen additions affect soil's microbial responses to PFASs. In this study, using a laboratory-based ecological experiment, we assessed the microbial availability of PFASs in soils receiving ammonium, nitrate, and urea nitrogen amendments by quantifying the translocation factors of PFASs from soil particle to soil extracellular polymeric substances (EPS). Our results showed that nitrogen, specifically ammonium, significantly increased the PFASs' microbial availability (p < 0.05). Second, nitrogen fertilization in PFASs-polluted soils decreased the microbial community diversity and stability at the structural, species, and functional levels (p < 0.05). For soil microbial activities, nitrogen enhanced the activity of superoxide dismutase (SOD) while it inhibited the catalase (CAT) and peroxidase (POD) (p < 0.01). Congruently, PFASs, as well as the nitrate and nitrite nitrogen, were shown to be the predominant abiotic drivers regulating the soil fungal succession (p < 0.05), while bacteria were mostly regulated by dissolved organic carbon (DOC) (p < 0.01). Furthermore, we revealed that the nitrogen cycling gene hmp (dominates the transformation from NO to NO₃^-) was the hub gene integrating the microbially available PFASs and the soil nitrogen cycling processes (p < 0.01), indicating that hmp could be the core regulator affecting the accumulation of PFASs in soil EPS. Our study highlighted that decreasing ammonia's amendments could mitigate China's national initiatives to reduce nitrogen fertilization in farmlands, reduce the PFASs' availability to the soil microbiome, and protect the microbial community stability in soil.

4F-Indole Enhances the Susceptibility of Pseudomonas aeruginosa to Aminoglycoside Antibiotics

Infections caused by multidrug-resistant bacteria are becoming increasingly serious. The aminoglycoside antibiotics have been widely used to treat severe Gram-negative bacterial infections. Here, we reported that a class of small molecules, namely, halogenated indoles, can resensitize Pseudomonas aeruginosa PAO1 to aminoglycoside antibiotics such as gentamicin, kanamycin, tobramycin, amikacin, neomycin, ribosomalin sulfate, and cisomicin. We selected 4F-indole as a representative of halogenated indoles to investigate its mechanism and found that the two-component system (TCS) PmrA/PmrB inhibited the expression of multidrug efflux pump MexXY-OprM, allowing kanamycin to act intracellularly. Moreover, 4F-indole inhibited the biosynthesis of several virulence factors, such as pyocyanin, type III secretion system (T3SS), and type VI secretion system (T6SS) exported effectors, and reduced the swimming and twitching motility by suppressing the expression of flagella and type IV pili. This study suggests that the combination of 4F-indole and kanamycin can be more effective against P. aeruginosa PAO1 and affect its multiple physiological activities, providing a novel insight into the reactivation of aminoglycoside antibiotics. IMPORTANCE Infections caused by Pseudomonas aeruginosa have become a major public health crisis. Its resistance to existing antibiotics causes clinical infections that are hard to cure. In this study, we found that halogenated indoles in combination with aminoglycoside antibiotics could be more effective than antibiotics alone against P. aeruginosa PAO1 and preliminarily revealed the mechanism of the 4F-indole-induced regulatory effect. Moreover, the regulatory effect of 4F-indole on different physiological behaviors of P. aeruginosa PAO1 was analyzed by combined transcriptomics and metabolomics. We explain that 4F-indole has potential as a novel antibiotic adjuvant, thus slowing down the further development of bacterial resistance.

QseB/QseC: a two-component system globally regulating bacterial behaviors

QseB/QseC is a two-component system that is involved in the regulation of multiple bacterial behaviors by regulating quorum sensing, bacterial pathogenicity, and antibiotic resistance. Thus, QseB/QseC could provide a target for new antibiotic development. Recently, QseB/QseC has been found to confer survival advantages to environmental bacteria under stress conditions. The molecular mechanistic understanding of QseB/QseC has become an active area of research and revealed some emerging themes, including a deeper understanding of QseB/QseC regulation in different pathogens and environmental bacteria, the functional difference of QseB/QseC among species, and the possibility of analyzing QseB/QseC evolution. Here, we discuss the progression of QseB/QseC studies and describe several unresolved issues and future directions. Resolving these issues is among the challenges of future QseB/QseC studies.