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  • Writer's pictureRoyston Cave

Microbiological Growth

Cracks in the chalk walls of Royston Cave have been colonised by microbiological growth, such as bacteria, fungi and algae. Microbiological growth is not only aesthetically unpleasant but, depending on the organism, can cause physical deterioration as the organisms attach themselves to the chalk. This aggravates existing geological processes and causes cracks to enlarge. Eventually, these sections of chalk crumble away. Chemical deterioration can also occur from the by-products of an organism's lifecycle.

In some parts of the cave, extensive areas of microbiological growth can be observed. Most of the growth is black or brown and hard to distinguish from dirt which has accumulated along the bottom of the cave.

Today, signs of microbiological growth are most obvious along the line of figures below the carving of St Christopher, but there has been evidence of microorganisms being present in Royston Cave for a long time. It was reported to be at its worst during the 1990s, when changes were made to the wiring in the cave and the lights were left on for long periods of time. This encouraged large areas of green algae growth in the vicinity of the lights, particularly on the northern and eastern sides of the cave where flooding had created damper conditions.

Detail of microbiological growth © Royston Cave.

A survey, carried out in 2004, identified three main organisms present in Royston Cave; a fungus called epenicillium chrysogenum which is mainly found in indoor environments, especially water-damaged buildings; a fungus called aspergillus niger, a common mould found on food; and a fungus called trichoderma viride which is used commercially to protect crops against other, more harmful fungi.

Patches of green microbiological growth were also identified, particularly an algae called Protococcus sp. which is commonly found on trees, rocks and soil. At the time, this algae was most noticeable on the eastern side of the cave, by the figure of St George, but it was also observed in the access tunnel near to the entrance and fluorescent lights. This indicated the photosynthetic nature of the organisms.

The main algae growth was tackled largely successfully at the time by turning off the cave lights and using biocidal UV lamps. Although algae can still be observed in the access tunnel, in the vicinity of the lights, these areas are small and largely under control.

Stone is a natural habitat for a range of microorganisms. In Royston Cave, as in many caves, its environmental conditions are relatively stable. Although nutrients are often limited, the moisture, high humidity and stable temperatures create a microclimate and provide an almost ideal condition for many microorganisms to survive and grow, regardless of external conditions.

The presence of these microorganisms usually then leads to the emergence of other organisms and complex ecosystems often develop. In Royston Cave, the combination of plants and animals, in its relatively gentle and stable microclimate, has created an ecosystem which is largely self-sustaining. Ecosystems like this can be so highly specialised and delicately balanced that even minor changes in environmental conditions can have dramatic effect on them.

Black and brown microbiological growth along the line of figures © Royston Cave.

In 2011, following conservation treatment to stabilise areas of chalk with calcium hydroxide in ethanol, black fungal growth appeared on some of the treated areas. This was unusual as the disinfectant qualities of the ethanol should have naturally killed any organisms present. Fungi also generally prefer lower acidity for growth but the application of the calcium hydroxide would have, if anything, increased the acidity of treated areas.

As a result of this new fungal growth, and as part of the wider process of attempting to conserve Royston Cave, a microbiological survey was carried out by Industrial Microbiological Services Ltd (IMSL) to identify the microorganisms present.

Samples were collected from the surface using sterile swabs moistened with distilled water. The swabs were then placed into individual containers for transportation to a laboratory.

The bacteria and fungal swabs were then streaked onto petri dishes containing agar and incubated at 20 °C for up to 10 days. The algae swabs were placed into tubes containing a nutrient solution and incubated at 20°C under light for up to 4 weeks. When suitable growth was observed, the species were able to be identified using a microscope.

The final report, published in 2012, indicated that a fungus called Gliomastix murorum may have been the cause of the black growth. It was suggested that some aspect of the conservation treatment had stressed a pre-existing organism which was previously present in an invisible form.

Its defence mechanism created a new black form with a high spore content which was then visible in treated areas. The black material was later removed from the cave with water swabs and has not reoccurred.

Generally though, the report showed that there were a very limited number of microorganism species present in Royston Cave. Gliomastix murorum was the dominant species of fungi but strains of Penicillium brevi-compactum were present in most samples as well. Two additional strains were also found but could not be grown in the lab and were therefore unidentifiable.

A limited number of bacteria species were found, mostly from the Bacillus genus. Other species are probably present elsewhere in the cave but only a few samples were taken at the time.

None of the species identified were human pathogens and no bacteria associated with sewage leaks was detected.

To minimise growth and activity by photosynthetic organisms, lighting in the cave is now limited. Chemical treatments are not recommended as chemicals might contaminate the water table or damage the cave’s delicate ecosystem.

Specimens of a fly and a larvae that were present in the cave were also collected as part of ISML's investigation. You can read about that report here.



Tobit Curteis Associates LLP. (2009). Condition Survey and Development of a Conservation Programme for Royston Cave, Hertfordshire.

Tobit Curteis Associates LLP. (2011). Preliminary Report on the Remedial Conservation Treatment at Royston Cave, Hertfordshire.

Industrial Microbiological Services LTD. (2012). Microbiological Survey of Selected Wall Surfaces at Royston Cave.

Tobit Curteis Associates LLP. (2014). Research and Conservation Treatment of Royston Cave, Hertfordshire.


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