Microbial degradation of dyes is vital to understanding the fate of dyes in the environment. In this study, a fungal strain A-3 and a bacterial strain L-6, which were identified as Aspergillus fumigatus and Pseudomonas fluorescens, respectively, had been proven to efficiently degrade crystal violet (CV) dye. The decolorization of CV dye by fungal and bacterial cocultivation was investigated. The results showed that the decolorization rate of cocultures was better than monoculture (P. fluorescens in L-6 (PF), and that of A. fumigatus A-3 (AF)). Furthermore, enzymatic analysis further revealed that Lac, MnP, Lip, and NADH-DCIP reductases were involved in the biodegradation of CV dyes. UV-visible spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, and gas chromatography-mass spectrometry (GC-MS) were used to examine the degradation products. GC-MS analysis showed the presence of 4-(dimethylamino) benzophenone, 3-dimethylaminophenol, benzyl alcohol, and benzaldehyde, indicating that CV was degraded into simpler compounds. The phytotoxicity tests revealed that CV degradation products were less toxic than the parent compounds, indicating that the cocultures detoxified CV dyes. As a result, the cocultures are likely to have a wide range of applications in the bioremediation of CV dyes.

Aims Root rot caused by Fusarium solani is an important disease seriously affecting the yield and quality of Astragalus membranaceus. Therefore, this study was performed to elucidate the antifungal activities and mechanisms of cinnamaldehyde treatment against F. solani and its control effect for A. membranaceus root rot. Methods and Results Cinnamaldehyde significantly inhibited mycelial growth and spore germination of F. solani in dose-dependent, and the median effective concentration was 178.68 μl l^-1. Furthermore, scanning electron microscopy (SEM), propidium iodide (PI) staining, cell leakage experiments and ergosterol quantitation illuminated that cinnamaldehyde could alter the mycelial morphology, damage the plasma membrane and hinder the biosynthesis of ergosterol. Besides, cinnamaldehyde induced the generation of reactive oxygen species (ROS) by synergistically upregulating the genes encoded subunits for NADPH oxidase. The disease suppression efficacy of 600 μl l^-1 cinnamaldehyde against A. membranaceus root rot was 92.98 ± 6.08% (P < 0.05) under greenhouse conditions. Conclusions This study proved that cinnamaldehyde could markedly inhibit the growth of F. solani in vitro and effectively suppress the occurrence of A. membranaceus root rot, perhaps by inducing oxidative damage, which results in the distortion of F. solani, and the destruction of cell membrane integrity and permeability. Significance and Impact of the Study This study first explores the antifungal mechanisms of cinnamaldehyde against F. solani in vivo and vitro, thereby providing a promising candidate for disease bio-control.

Potato black scurf, caused by Rhizoctonia solani, is a severe soil-borne disease that affects the quality and production of potatoes worldwide. In our study, we used Paenibacillus polymyxa YF and Bacillus amyloliquefaciens HT to determine the antagonistic ability of R. solani, with a particular focus on the antagonistic action of P. polymyxa YF to R. solani and its biocontrol effect on potato black scurf. In fermentation, filtrate assay, 50% filtrate of P. polymyxa YF and B. amyloliquefaciens HT inhibited the growth of R. solani by 85.55% and 82.86%, respectively. Microscopic observations showed notable morphological changes with mycelial collapse, atrophy, and deformation following treatment with the antagonistic filtrates. Moreover, cell membrane permeability results showed increased conductivity in bacteria-treated samples compared to the control. P. polymyxa YF exhibited stable colonization on potato plants and secreted various extracellular enzymes (protease, amylase, and cellulase), along with the synthetic substances with growth-promoting effects, such as siderophores and Indole-3-acetic acid (IAA). Whether it is in the excised tissue inoculation or potted experiment, the negative control showed the highest rank of disease symptoms. In the pot experiment, after YF treatment, physiological parameters showed remarkable changes in plant height, root length, stem thickness, and dry and fresh weight. Compared to blank control, the activities of the four resistant enzymes increased significantly in the P. polymyxa YF treatment group. The upregulation in the P. polymyxa YF group was 4.04, 0.54, 0.46, and 3.10 times, respectively. PCR analysis identified genes in both bacterial strains coding for antimicrobial lipopeptides, including fenB, ituC, and srfAA, which are associated with fengycin, iturin, and surfactin synthesis. These findings demonstrated that P. polymyxa YF has a prominent antagonistic effect on R. solani, suggesting its potential as an effective biological control agent for controlling potato black scurf.