De Novo Design of Antimicrobial Peptides With a Special Charge Pattern and Their Application in Combating Plant Pathogens

Scientific and technological advances in the development of sustainable disease management tools: a case study on kiwifruit bacterial canker

Plant disease outbreaks are increasing in a world facing climate change and globalized markets, representing a serious threat to food security. Kiwifruit Bacterial Canker (KBC), caused by the bacterium Pseudomonas syringae pv. actinidiae (Psa), was selected as a case study for being an example of a pandemic disease that severely impacted crop production, leading to huge economic losses, and for the effort that has been made to control this disease. This review provides an in-depth and critical analysis on the scientific progress made for developing alternative tools for sustainable KBC management. Their status in terms of technological maturity is discussed and a set of opportunities and threats are also presented. The gradual replacement of susceptible kiwifruit cultivars, with more tolerant ones, significantly reduced KBC incidence and was a major milestone for Psa containment - which highlights the importance of plant breeding. Nonetheless, this is a very laborious process. Moreover, the potential threat of Psa evolving to more virulent biovars, or resistant lineages to existing control methods, strengthens the need of keep on exploring effective and more environmentally friendly tools for KBC management. Currently, plant elicitors and beneficial fungi and bacteria are already being used in the field with some degree of success. Precision agriculture technologies, for improving early disease detection and preventing pathogen dispersal, are also being developed and optimized. These include hyperspectral technologies and forecast models for Psa risk assessment, with the latter being slightly more advanced in terms of technological maturity. Additionally, plant protection products based on innovative formulations with molecules with antibacterial activity against Psa (e.g., essential oils, phages and antimicrobial peptides) have been validated primarily in laboratory trials and with few compounds already reaching field application. The lessons learned with this pandemic disease, and the acquired scientific and technological knowledge, can be of importance for sustainably managing other plant diseases and handling future pandemic outbreaks.

Visualizing the membrane disruption action of antimicrobial peptides by cryo-electron tomography

The abuse of antibiotics has led to the emergence of multidrug-resistant microbial pathogens, presenting a pressing challenge in global healthcare. Membrane-disrupting antimicrobial peptides (AMPs) combat so-called superbugs via mechanisms different than conventional antibiotics and have good application prospects in medicine, agriculture, and the food industry. However, the mechanism-of-action of AMPs has not been fully characterized at the cellular level due to a lack of high-resolution imaging technologies that can capture cellular-membrane disruption events in the hydrated state. Previously, we reported PepD2M, a de novo-designed AMP with potent and wide-spectrum bactericidal and fungicidal activity. In this study, we use cryo-electron tomography (cryo-ET) and high-speed atomic force microscopy (HS-AFM) to directly visualize the pepD2M-induced disruption of the outer and inner membranes of the Gram-negative bacterium Escherichia coli, and compared with a well-known pore-forming peptide, melittin. Our high-resolution cryo-ET images reveal how pepD2M disrupts the E. coli membrane using a carpet/detergent-like mechanism. Our studies reveal the direct membrane-disrupting consequence of AMPs on the bacterial membrane by cryo-ET, and this information provides critical insights into the mechanisms of this class of antimicrobial agents.

Methylarsenite is a broad-spectrum antibiotic disrupting cell wall biosynthesis and cell membrane potential

Methylarsenite (MAs(III)), a product of arsenic biomethylation or bioreduction of methylarsenate (MAs(V)), has been proposed as a primitive antibiotic. However, the antibacterial property and the bactericidal mechanism of MAs(III) remain largely unclear. In this study, we found that MAs(III) is highly toxic to 14 strains of bacteria, especially against 9 strains of Gram-positive bacteria with half maximal inhibitory concentration (IC50) in the sub micromolar range for Staphyloccocus aureus, Microbacterium sp., Pseudarthrobacter siccitolerans and several Bacillus species. In a co-culture of B. subtilis 168 and MAs(III)-producer Enterobacter sp. CZ-1, the later reduced non-toxic MAs(V) to highly toxic MAs(III) to kill the former and gain a competitive advantage. MAs(III) induced autolysis of B. subtilis 168. Deletion of the autolysins LytC, LytD, LytE, and LytF suppressed MAs(III)-induced autolysis in B. subtilis 168. Transcriptomic analysis showed that MAs(III) downregulated the expression of the major genes involved in the biosynthesis of the cell wall peptidoglycan. Overexpression of an UDP-N-acetylglucosamine enolpyruvyl transferase gene murAA alleviated MAs(III)-induced autolysis in B. subtilis 168. MAs(III) disrupted the membrane potential of B. subtilis 168 and caused severe membrane damage. The results suggest that MAs(III) is a broad-spectrum antibiotic preferentially against Gram-positive bacteria by disrupting the cell wall biosynthesis pathway and cell membrane potential.

Patent Highlights June–July 2022

A snapshot of noteworthy recent developments in the patent literature of relevance to pharmaceutical and medical research and development.