A preliminary comparative study of microbial communities colonizing ochre-decorated chambers at the Hal Saflieni Hypogeum at Paola, Malta

Abstract

The Ħal Saflieni Hypogeum at Paola, Malta, a UNESCO World Heritage Site, has been under strict climatic control and visitor influx since the late 1990s. The site is monitored regularly, with special attention being given to the ochre-decorated rock surfaces, which date back to 3300-3000 BC. As part of the monitoring exercise, alterations on the surface of the ochre-decorated chambers have been studied over the past years in order to understand whether changes in microclimatic parameters have led to a change in the microbial community previously described. Biofilms were sampled using non-invasive techniques, and studied using microscopy, culture and molecular techniques. Extensive white alterations were due to chemoorganotrophic bacteria belonging to morphologically diverse groups. These organisms were the main colonizers of the ancient ochre-decorated surfaces. Remains of past extensive algal colonizations were evident, and physiologically active cells survive in biofilms even though the irradiance and duration of photoperiod have been drastically reduced. Fungi were occasionally isolated, though considered air contaminants.