Cercosporin

In the present work, we study the photodynamic action of cercosporin (cerco), a naturally occurring photosensitizer, on human cancer multicellular spheroids. U87 spheroids exhibit double the uptake of cerco than T47D and T98G spheroids as shown by flow cytometry on the single cell level. Moreover, cerco is efficiently internalized by cells throughout the spheroid as shown by confocal microscopy, for all three cell lines. Despite their higher cerco uptake, U87 spheroids show the least vulnerability to cerco-PDT, in contrast to the other two cell lines (T47D and T98G). While 300 μm diameter spheroids consistently shrink and become necrotic after cerco PDT, bigger spheroids (>500 μm) start to regrow following blue-light PDT and exhibit high viability. Cerco-PDT was found to be effective on bigger spheroids reaching 1mm in diameter especially under longer exposure to yellow light (~590 nm). In terms of metabolism, T47D and T98G undergo a complete bioenergetic collapse (respiration and glycolysis) as a result of cerco-PDT. U87 spheroids also experienced a respiratory collapse following cerco-PDT, but retained half their glycolytic activity.

Pseudocercosporella capsellae, the causative agent of white leaf spot disease in Brassicaceae, can produce a purple-pink pigment on artificial media resembling, but not previously confirmed as, the toxin cercosporin. Chemical extraction with ethyl acetate from growing hyphae followed by quantitative (thin-layer chromatography [TLC] and high-performance liquid chromatography [HPLC]) and qualitative methods showed an identical absorption spectrum, with similar retardation factor (Rf) values on TLC papers and an identical peak with the same retention time in HPLC as for a standard for cercosporin. We believe this is the first report to confirm that the purple-pink pigment produced by P. capsellae is cercosporin. Confocal microscopy detected green autofluorescence of cercosporin-producing hyphae, confirming the presence of cercosporin inside hyphae. The highly virulent UWA Wlra-7 isolate of P. capsellae produced the greatest quantity of cercosporin (10.69 mg g-1). The phytotoxicity and role of cercosporin in disease initiation across each of three Brassicaceae host species (Brassica juncea, B. napus, and Raphanus raphanistrum) was also studied. Culture filtrates containing cercosporin were phytotoxic to all three host plant species, producing large, white lesions on highly sensitive B. juncea, only water-soaked areas on least sensitive R. raphanistrum, and intermediate lesions on B. napus. It is noteworthy that sensitivity to cercosporin of these three host species was analogous to their susceptibility to the pathogen, viz., B. juncea the most susceptible, R. raphanistrum the least susceptible, and B. napus intermediate. The presence of cercosporin in the inoculum significantly increased disease severity on the highly cercosporin-sensitive B. juncea. We believe that this is the first study to demonstrate that P. capsellae produces cercosporin in liquid culture rather than agar media. Finally, this study highlights an important role of cercosporin as a pathogenicity factor in white leaf spot disease on Brassicaceae as evidenced by the ability of the cercosporin-rich culture filtrate to reproduce white leaf spot lesions on host plants and by the enhanced virulence of P. capsellae in the presence of cercosporin.

Pharmaceuticals have seriously contaminated aquatic environments and resulted in the formation of drug-tolerant bacteria owing to continuous release and accumulation. Therefore, the development of new methods to simultaneously decompose drugs and disinfect pathogens in an environmental-friendly manner with high efficiency is still in great demand. Bioinspired by the great photosensitivity of natural product cercosporin with the ability to efficiently generate reactive oxygen species (ROS) under natural sunlight and its antibacterial activity, here a novel cercosporin/polymethylmethacrylate (CP/PMMA) photocatalyst was rationally developed by incorporating and restricting cercosporin in a "green" macroporous resin PMMA, which greatly improved the ROS generation efficiency and displayed 97.2-100% photodegradation for broad-spectrum pharmaceuticals, including fluoroquinolones, trimethoprim and chloroquine phosphate, upon 15 W compact fluorescent lamp irradiation. More importantly, this decontamination efficiency was greatly improved, and the decontamination time was substantially shortened in a large-scale assay under natural sunlight. Furthermore, it could inactivate the pathogen Staphylococcus aureus. Overall, this work provides new insight into how a multifunctional photocatalyst could be designed using a natural product and macroporous resins for environmental remediation.