You may have heard of 'painting with bacteria' and the American Society for Microbiology's annual agar art competition, if not, it's definitely worth checking out: ASM Agar Art Contest.

But have you heard of bacteria destroying artwork? To be honest, we'd not given it much thought either – until we came across an academic journal article discussing a study on oil paintings and microbes. The damage done is called bio-deterioration / microbial decay and is of particular concern in older paintings.

Once we read about it, we were glad of the opportunity to learn about another aspect of the microbial world that we'd not paid much attention to previously. The below is some of what we went on to discover….

Surprisingly, it isn't only old paintings that are affected by microbial bio deterioration. Risk factors for this are related to other things such as the materials used and the conditions in which the paintings are stored or displayed.¹ High humidity and temperatures of between 20 to 30°C often contribute to the chances of bio deterioration occurring as these are the conditions ideal for microbial growth.² The environment in which the painting is displayed is subject to daily temperature fluctuations and other disturbances such as visitor activity, air flow, sunlight exposure and moisture from condensation / high humidity.³ These factors all play a part in providing the conditions that bacteria, yeasts and fungi love.

As mentioned above, materials used can increase the risk of bio deterioration as many of them are organic materials. These include textiles, gelatin, egg yolk, flour, milk casein and oil (among others). Organic components are perfect 'food sources' for micro-organisms and are therefore more likely to encourage microbial growth and in turn – bio deterioration.⁴ Dirt, dust and soot that settles on the painting may also provide nutrients for microbes.⁵

Interestingly, microbial communities found in paintings are usually one group of microbe such as bacteria or fungi, rather than a mixture of them.⁶ This could be due to a number of factors including different species preferring the nutrients provided by particular organic components in the painting. It could be that the environmental conditions are more suited to one type of micro-organism. Another possibility is that bacteria could have thrived so well under the particular conditions provided within the painting and its environment, that it outcompeted and overwhelmed any fungi (or vice versa).

So what are the tell tale signs of microbial degradation?

Common indicators of bio deterioration are stains, dust, discolouration, cracking, paint degradation and bubbling. Although other damage may occur depending on the types of microbes involved and the level of contamination.

In one study (only looking at fungal contamination), twenty one fungal colonies were isolated in the paintings that were analysed. These colonies included a variety of species including Penicillium spp which is known to be a prevalent presence within paintings.⁷ Another study found that different types of bacteria colonised different areas of oil paintings. Where these species specific ecosystems occurred was found to be dependent on environmental conditions such as temperature and nutrients.⁸ This was also the case with fungi found on the painting with specific fungi growing on different coloured pigments.⁹

How bad can microbial degradation become?

When an infection is particularly bad, it can cause severe damage including holes within the canvas. In this case, the entirety of the painting including the frame and underframe requires sterilisation.¹⁰

Famous and beloved artworks haven't escaped destruction due to microbes. We even came across a study looking at bio deterioration of Edvard Munch's paintings.¹¹

Bacteria: Artwork destroyer or saviour?

So, we've looked at ways in which microbes are damaging paintings but we're pleased to tell you that they are helping to save them too.

Specific micro-organisms can be used in the fight against microbial degradation. Microbial treatments are being developed as an alternative to chemical cleaning methods.¹³ When it comes to bio treatments, bacteria are (in recent times) being utilised more than fungi for this purpose.¹⁴ One study tested the efficacy of Bacillus bacteria as a potential treatment for biodeterioration in paintings. It was found that the bacteria inhibited growth of most strains of microbes that were isolated from the painting that was tested¹⁵.

This isn't the only recent example of bacteria being utilised as a cleaning agent. In another case, a biogel was used to clean wall paintings at the Vatican museums. Instead of Bacillus bacteria, Pseudomonas stutzeri cells were used.¹⁶ After this biocleaning was performed, the paintings were monitored for microbial growth for two months. A very small amount of viable microbial cells were detected in this time.¹⁷ The authors of the study note that a selective cleaning process would be required after biocleaning to ensure that the strain used to clean does not develop into a biodeterioration risk itself.¹⁸.

Hopefully this offers a balanced perspective of how (as in most circumstances) microbes can be a force for good as well as the not so good. Also, next time you're in an art gallery, looking at the artwork, consider that there may be more to it than meets the eye (literally!).

References

1, 2, 3, 4, 7: V?car CL, Mircea C, Pârvu M, Podar D. Diversity and metabolic activity of fungi causing biodeterioration of canvas paintings. Journal of Fungi. 2022;8(6):589. doi:10.3390/jof8060589

5, 6 : Ciferri O. Microbial degradation of paintings. Applied and Environmental Microbiology. 1999;65(3):879-885. doi:10.1128/aem.65.3.879-885.1999 

8, 10: Berovi? M. Biodeterioration studies on pastels and oil-based paintings. In: Koestler RJ, Koestler VH, Charola AE, Nieto - Fernandez FE, eds. Art, Biology and Conservation: Biodeterioration of Works of Art. New York: Metropolitan Museum of art; 2003:58.

11: Salvador C, Sandu ICA, Sandbakken E, Candeias A, Caldeira AT. Biodeterioration in art: A case study of munch's paintings. The European Physical Journal Plus.2002; 137:11. doi:10.1140/epjp/s13360-021-02187-0

12, 13: Pyzik A, Ciuchcinski K, Dziurzynski M, Dziewit L. The Bad and the Good-Microorganisms in Cultural Heritage Environments-An Update on Biodeterioration and Biotreatment Approaches. Materials (Basel). 2021;14(1):177. doi:10.3390/ma14010177

9, 14, 15: Caselli E, Pancaldi S, Baldisserotto C, et al. Characterization of biodegradation in a 17th century easel painting and potential for a biological approach. PLOS ONE. 2018;13(12). doi:10.1371/journal.pone.0207630

16, 17, 18: Ranalli G, Zanardini E, Rampazzi L, et al. Onsite advanced biocleaning system for historical wall paintings using new agar-gauze bacteria gel. Journal of Applied Microbiology. 2019;126(6):1785-1796. doi:10.1111/jam.14275