Paintings are a Canvas for Microbial Life
Figure 1. Abbott Lawrence by G.P.A. Healy. A 19th century painting before and after restoration. Source.
Art provides insight into our heritage and past. It tells a story of who we were and who we are now. Yet, art is often lost to fire, flood, or deterioration, so we go to great lengths to protect the remnants of our history (Fig. 1). Varnish applied to paintings helps keep dust, dirt, and moisture at bay. Drawing curtains prevents ultraviolet light from fading the brilliant colors on a canvas. We do so much to preserve our past, but we still have a lot to learn about protecting art from biodeterioration.
Dennis Allsopp, a mycologist and biodiversity coordinator of the Centre for Agriculture and Bioscience International, defines biodeterioration as “any undesirable change in a material brought about by the vital activities of organisms.” Fungi, bacteria, archaea, and lichen have been found in all types of arts, from the ancient to the modern. As paintings age, they accumulate volatile hydrocarbons, cigarette smoke, and even dead or living cells. Dust particles that collect on surfaces bring fungal spores and bacteria along with them. This agglomeration of material serves as a nutrient source for a number of microbes.
Microbes not only thrive off of the material accumulating on paintings, some also consume the molecules found in paints or the canvas itself. Paint consists of three main components: the binder matrix (holds paint together and helps it adhere to surfaces), the pigments and extenders (for color and build), and the solvent (which can be organic or water-based). Additives (less than 5% of paint) include thickeners (cellulose-based), emulsifiers, plasticizers, and colloids. Canvas surfaces, often made of cellulose, can be a particularly good carbon source for microbes, but all these things can make a great feast for the right microbes.
To find what microbes inhabit paintings, López-Miras and colleagues analyzed the microbial composition of the “Virgen de Guadalupe,” an oil painting on canvas that showed signs of biodeterioration (Fig. 2). This painting was exhibited at the convent of San Antón in Granada, Spain. The group isolated bacterial species belonging to Bacillus and Paenisporosarcina genera, but the majority of the nonculturable species (those identified by sequencing) belonged to the phylum Proteobacteria. Isolated fungal species belonged to Penicillium and Eurotium, but the majority of nonculturable fungi belonged to the order Pleosporales and Saccharomycetales.
Figure 2. “Virgen de Guadalupe” (oil on canvas). Sampling areas are indicated. Source: López-Miras et al.
Though these species were isolated from the paintings, it doesn’t mean that all of them participate in biodeterioration. Some may be ubiquitous airborne organisms that do not cause damage. Thus, the researcher created “mock paintings” that simulated the original painting composition and inoculated specific bacterial and fungal strains both alone and in combinations to determine their potential for microbial degradation. One notable example is that of the bacterium Arthrobacter sp. and the fungus Penicillium sp. Alone, neither species affected the painting. But when put together, the authors noticed chemical changes on the mock painting. The fungus generates an enzyme capable of breaking down bacterial cell walls and the authors think that the dead bacterial cells stick onto the painting and support fungal growth over the painting.
So how can we preserve vulnerable art? Should we use antimicrobials in art restoration and conservation? Chemical treatments include a wide variety of alcohols, aldehydes, phenols, and acid, among others. However, only a small number of these agents are tested for compatibility with the materials used to create the art; we do not know how these chemicals will affect the art. Additionally, microbial communities are often mixed communities with different tolerances to the chemicals used.
Antimicrobial paints are now marketed for use in homes and healthcare settings. The addition of silver nanoparticles is what makes paint antimicrobial; the nanoparticles interact with bacteria and burst the cells. However, these particles are not specific and they hit both pathogens and nonpathogens. “It is more or less like a soaping or detergent effect,” Lucian Lucia, associate professor at North Carolina State University, describes in an interview with Live Science.
But as microbes are always evolving, will antimicrobials actually serve a purpose in the long run? Lucia does not think that resistance to silver nanoparticles will develop. Because the silver nanoparticles destroys the surface of the cells, they do not target specific bacterial activities the way antibiotics do. Other chemical efforts to preserve art, however, may foster the emergence of antimicrobial-resistant organisms. But both silver nanoparticles and antimicrobial treatments can disrupt the balance of microbes in our built and natural environments.
Is the biodeterioration of cultural artifacts something we can or should try to stop? Is it a battle we cannot win, something we have to accept as a natural process? We do so much to protect human history, yet most things ultimately succumb to microbial decay. But until that time comes, we strive to protect these stories from our history for as long as we can.
- Contribution of the Microbial Communities Detected on an Oil Painting on Canvas to Its Biodeterioration
- Microbial deterioration of cultural heritage and works of art – tilting at windmills?
- Art, Biology, and Conservation: Biodeterioration of Works of Art