Bacteria and fungi keep some ancient Australian rock art colors vivid

Jan 06, 2011 by Lin Edwards report
(Scale bar = 1mm. Rectangle left shows approximate location of digital micrograph illustrated right). High magnification view of biofilm in the centre of a Bradshaw painting. Image credit: Jack Pettigrew et al.

(PhysOrg.com) -- New studies of 80 Bradshaw rock art works in the Kimberley region of Western Australia have shown their colors have not faded because the artworks are coated with a biofilm of bacteria and fungi.

The Bradshaw art works are named after Joseph Bradshaw, a 19th century pastoralist who was the first white settler to discover them. They are known locally as Gwion Gwion. The paintings are estimated to be at least 17,000 years old, and possibly as ancient as 70,000 years old, based on the time of extinction of animals and plants depicted. The paintings are often vivid and have high contrast, even though they are often exposed to the elements, and they are not thought to have been repainted. Other rock art in the same region fades over centuries and is often repainted.

Two of the oldest types of Bradshaw are known as Sash and Tassel, and a research team led by Professor Jack Pettigrew of the University of Queensland studied paintings of these types from 16 sites, using equipment such as portable digital microscopes. They chose the Sash and Tassel styles because there is less controversy about their classification and because they are accepted as the oldest examples of Bradshaw art.

The team found in almost all the paintings the original paint pigments had been replaced by pigmented microbes, which the researchers dubbed “living pigments.”

Professor Pettigrew said the organisms were still living and successive generations would have lived in the paintings for thousands of years, which explains the fresh appearance of the paintings.

One of the many organisms colonizing the works is a black fungus, which is thought to belong to the Chaetothyriales group. These fungi survive by cannibalizing their predecessors in situ. If the original paint contained fungus spores the current organisms could be directly descended from these spores. The researchers found that in 98 percent of cases the fungi remained within the boundaries of the painting, but there were a few examples where the fungi had destroyed most of the art work.

Another organism found is an as-yet unidentified red bacterium, which may be a species of Cyanobacteria. The red were often found with the black fungus. The combination of the two produces colors including red, black, mulberry, and cherry.

Professor Pettigrew and colleagues also speculate the paint used may have contained nutrients that “kick-started” a symbiotic relationship between the black fungi and red bacteria, with the bacteria providing carbohydrates to the fungi via photosynthesis, and the providing water to the bacteria.

The presence of living organisms on the paintings could explain why results of attempts to date the paintings have been inconsistent. Professor Pettigrew said a possible way to date the may be to determine the DNA sequence evolution, and work on this has already begun.

Explore further: Two-armed control of ATR, a master regulator of the DNA damage checkpoint

More information: Living pigments in Australian Bradshaw rock art - antiquity.ac.uk/projgall/pettigrew326/

Related Stories

New technology for dating ancient rock paintings

Mar 11, 2009

A new dating method finally is allowing archaeologists to incorporate rock paintings — some of the most mysterious and personalized remnants of ancient cultures — into the tapestry of evidence used to study life in prehistoric ...

A bird's eye view of art

Jun 30, 2009

Pigeons could be art critics yet, according to a new study which shows that like humans, pigeons can be trained to tell the difference between 'good' and 'bad' paintings. According to Professor Shigeru Watanabe from Keio ...

Ancient cave paintings found in Romania

Jun 13, 2010

Romanian experts have discovered the most ancient cave paintings found to date in Central Europe, aged up to 35,000 years old, Romanian and French scientists said Sunday.

Recommended for you

Japanese scientist resigns over stem cell scandal

Dec 19, 2014

A researcher embroiled in a fabrication scandal that has rocked Japan's scientific establishment said Friday she would resign after failing to reproduce results of what was once billed as a ground-breaking study on ...

'Hairclip' protein mechanism explained

Dec 18, 2014

Research led by the Teichmann group on the Wellcome Genome Campus has identified a fundamental mechanism for controlling protein function. Published in the journal Science, the discovery has wide-ranging implications for bi ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.