painting with biofilms

[eub]

http://antiquity.ac.uk/projgall/pettigrew326/

The age of Bradshaw rock art (also called gwion gwion) is uncertain but estimated by indirect methods at between 46 000 years ago, based on the time of extinction of depicted live megafauna (Roberts & Brook 2010), and 70 000 years ago, which is the age of the boab tree in Australia. In view of this antiquity, it is remarkable that Bradshaw paintings, often exposed to sun and rain, can be vivid and with high contrast, even though they have never been repainted. Conversely, other rock art in the same region, such as the Wandjina paintings, fades at a rate measured in hundreds of years and is often repainted. Here we report on cases where the original paint is no longer present in Bradshaw art, but has been replaced by a biofilm of living, pigmented micro-organisms whose natural replenishment may account for the longevity and vividness of these ancient paintings.

They find a fungus which they tentatively identify in the Chaetothyriales, and colonies they can't resolve to cells in the field but suspect to be cyanobacterial. (They report that they swabbed DNA, which they'll follow up with.)

An obvious question is why the biofilm continues to respect the original boundaries of the painting. The authors speculate "The etched cavities and pores providing microenvironments will exactly follow the shape of the painting if the original paint contained silica-dissolving microbes or acid capable of dissolving the cement between the silica grains." (They also suggest other reasons, but I didn't follow quite how they addressed the question.)

Comments

[eub.livejournal.com]

Looking in Alexopoulos, Mims, and Blackwell to see if they talk about Chaetothyriales with cyanobacterial photobionts. Strigula elegans forms a lichen with Cephaleuros, a green alga. Which on its own lives as a parasite, economically important on coffee. Cool, I didn't know about parasitic green algae.

The Google snippet gives an Ann. Rev. Phytopathol. article enthusiastically titled PARASITIC GREEN ALGAE!, but the ! is sadly a mis-OCR of a ¹.)

[eub.livejournal.com]

Tangentially, rhodophytes with a 3-cycle "alternation" of generations!

http://tolweb.org/Florideophyceae

Figure 3. Diagram of triphasic life history. Haploid (1N) male gametophytes produce spermatia that are released, while haploid female gametophytes produce carpogonia (=egg cells) that are retained on the female gametophyte. After fertilization, the diploid (2N) zygote is still retained on the female gametophyte and develops into the diploid carposporophyte. The carposporophyte produces diploid carpospores that are released and develop into the diploid tetrasporophyte. The tetrasporophyte produces tetrasporangia where meiotic divisions result in haploid tetraspores. These tetraspores then develop into haploid gametophytes completing the life cycle.