Get Outside—Nature Is Antimicrobial!
High anxiety now pervades our daily life. It seems everything we might touch, be it a ceramic door knob, a stainless steel handle, a glass pitcher, or a plastic keyboard may be harboring the packets of virulent DNA we otherwise call a virus. To ease that anxiety, we’d do well to get outside and connect with nature to soothe our souls and soften our blood pressure. While you’re immersing yourself in the beautiful sights, scents, and sounds of the natural world, it might put a smile on your face to know that emerging from the wisdom of 3.8 billion years of evolution, nature has figured out how to make her materials–ranging from leaves, flower petals, and insect wings to horns, beaks, and feathers–inhospitable to microbes. There is so much nature could teach us about how to design our surfaces so that they become a dead-end for pathogens.
How does nature do that?
While it’s long been recognized that exposure to the sun’s disinfecting ultraviolet (UV) radiation will kill off microbes, sun isn’t always guaranteed. Organisms have developed an abundance of strategies to thwart the efforts of would-be microscopic villains–a vast library of strategies to inspire novel ways of protecting human health from future pandemics.
Tasteful protection
One common approach in nature is to expand the job description of flavors and fragrances. For example broccoli, turnips, horseradish, kale, and watercress–members of the Brassicaceae family–produce a variety of isothiocyanate compounds that provide attractive and sometimes strong flavors for organisms that ultimately spread the Brassicaceae family seeds. They serve a dual function though. While waiting to serve themselves up, these flavor compounds protect the plant from microbial predators by clinging fiercely to key molecules in the predator’s biochemical arsenal, thereby stopping the infection process in its tracks.
Similarly, American pokeweed (Phytolacca americana) produces a highly effective compound against a range of pathogenic viruses. This compound could inspire the development of new health interventions to combat disease-causing viruses. However, pokeweed itself is toxic to humans, so best not mix pokeweed into your salad or smoothie to ward off COVID-19!
The smell of success
The sweet fragrance of palmarosa (Cymbopogon martinii) is borne of scent molecules (terpene alcohols) that protect this species of lemongrass by killing and/or repelling predator microbes. Many plants have compounds that do more than smell nice. Tufted titmouse birds (Baeolophus bicolor) keep microbes away from young nestlings by lining their nests with aromatic herbs, offering an array of pharmaceutical options to research.
In contrast, the roots of maize seedlings utilize a different, but common antimicrobial strategy. They produce a “scent” compound that is not only directly toxic to a pathogenic soil microbe, it also attracts another microbe (P. putida) that suppresses the population of any remaining pathogens that survive the opening act by outcompeting them for a limited supply of nutrients.
Color me microbe-free
The brilliant colors of parrot feathers not only serve to signal social standing, health status, and fashion choices, they also protect feathers from microbial degradation. The carotenoid pigments of the blue-crowned parakeets (Aratinga acuticaudata) impart this species with unusual resistance to microbial degradation. Like melanin, these colorful pigments thicken the outer layer of the feather’s central barb making it more difficult for pathogenic microbes to break through.
Antimicrobial beauty is only skin deep
Up to 25,000 different species of teleost fish secrete a protective mucus coating containing a host of antimicrobial proteins including defensins. Defensins acquire their functionality based on their unique 3D shape because, like all proteins, defensins work by fitting hand-in-glove with their target molecule (perhaps a key protein on the surface of a microbe) triggering a cascade of chemical choreography leading to the dramatic final scene of the cell’s demise. Chinese softshell turtles (Pelodiscus sinensis) took a page out of the teleost fish recipe book by creating a protein, called pelovaterin, that mimics part of the shape of the defensin molecule. Pelovaterin plays a key role in facilitating the mineralization process of the turtle’s eggshells while also protecting the developing embryo from microbial invasion.
Parents blowing soap bubbles bring children sheer delight for the fleeting seconds these delicate, watery spheres hold their shape. While we might wish these would last for days, the common mud puddle foam nesting frog (Engystomops pustulosus) made that a reality for its offspring eons ago. Lectins, carbohydrate-binding proteins, are the key players in this scene. Like pelovaterin, they also impart antimicrobial activity that protects the growing tadpoles within the foam nest.
Not-so-smooth operator
While chemistry is often a solution in nature, surface microtextures can also inhibit microbes. The eggshells of the white dogwhelk (Dicathais orbita) ward off microbial attack with a regularly patterned nano-ridged surface that disrupts microbial attachment. Ridges found at the microscopic scale on many species of sharks are also known to inhibit bacterial attachment and growth.
Biomimetic solutions laying in wait
Viruses have been on the planet since the dawn of life. This means every species at some level has developed strategies to adapt to their impact. So when you’re out in nature smelling the herbs, drinking in the sounds, and gazing at the shapes, colors and textures of the myriad natural materials making up the ecosystem of your choice, know that we’ve only scratched the surface of a world of time-tested strategies waiting to inspire new public health approaches worthy of the 21st century.
Now, let’s get to work!
Partial list of references
Aires, A., Carvalho, R., Barbosa, M., Rosa, E. (2009). “Suppressing Potato Cyst Nematode, Globodera rostochiensis, with Extracts of Brassicaceae Plants” American Journal of Potato Research 86(4), 327-333. https://dx.doi.org/10.1007/s12230-009-9086-y
Burtt, E., Schroeder, M., Smith, L., Sroka, J., McGraw, K. (2010). “Colourful parrot feathers resist bacterial degradation” Biology Letters 7(2), 214-216. https://dx.doi.org/10.1098/rsbl.2010.0716
Chen, W., Viljoen, A. (2010). “Geraniol — A review of a commercially important fragrance material” South African Journal of Botany 76(4), 643-651. https://dx.doi.org/10.1016/j.sajb.2010.05.008
Esteban, M. (2012). “An Overview of the Immunological Defenses in Fish Skin” ISRN Immunology 2012(), 1-29. https://dx.doi.org/10.5402/2012/853470
Ntalli, N., Caboni, P. (2017). “A review of isothiocyanates biofumigation activity on plant parasitic nematodes” Phytochemistry Reviews 16(5), 827-834. https://dx.doi.org/10.1007/s11101-017-9491-7
Vasickova, P., Pavlik, I., Verani, M., Carducci, A. (2010). “Issues Concerning Survival of Viruses on Surfaces” Food and Environmental Virology 2(1), 24-34. https://dx.doi.org/10.1007/s12560-010-9025-6