This lecture is part of the 2009 Nationwide Cemetery Preservation Summit
Algal Populations on Military Gravestones and Possible Control by Biological Methods
Green algae are common colonizers of stone throughout the world and reports of the growth of this group of organisms on buildings and monuments come from across Europe, south-east Asia, Central, North and South America. Standard treatment methods to date have centered on abrasive and chemical treatments rather than biologically-based solutions.
It is widely accepted that risk assessments for any treatment should include the potential for re-growth or accelerated growth and any impact upon the structure of the stone. In addition, chemical treatments are increasingly subject to tighter control from an environmental aspect. In recent years, ecological studies of naturally-occurring biological control of aquatic algae have focused on viruses, which cause lysis and subsequent death of the host organism. Viruses are found in sediments and are believed to be important in natural control of algal populations. This paper will describe pilot studies to assess the relative effectiveness and impacts of bioremediation by viruses for removal of growths of algae from Portland limestone.
Our research was concerned with testing the feasibility of using viruses that pose no health threat to humans to control natural algal populations on stone. Two surveys were conducted at the Brookwood Military Cemetery in Surrey, UK and data were collected on patterns of algal cover on headstones. Algal cover was highly variable within the sections of cemetery sampled. Proximity of tree cover or shading vegetation, age of headstone, and front versus back aspect of headstone all appear to be influential on algal contamination. Three zones of algal cover are evident on headstones, at the crown, the base and the central area of the headstone and this is common to both faces.
The analysis of microorganism diversity suggested that the diversity of each of these zones to be different. Patterns of microorganism diversity suggested that a number of different taxa are common across groups of headstones samples from Brookwood. Much of the work that has been done on algal viruses has been for aquatic systems but the presence of naturally-occurring viruses in isolation plates was demonstrated for Brookwood headstones.
Although we were able to identify viruses using fluorescence microscopy, we were not able to isolate and amplify these viruses in the laboratory. Nevertheless, using paired algal hosts and viruses from aquatic systems, we obtained evidence that they can inhibit algal populations on stone in laboratory culture. Our results demonstrate proof of principle that algal types that are commonly found on the stones can be inhibited by viruses on stone in the laboratory.
Dr. Eric May is a professor of Microbiology at the University of Portsmouth School of Biological Sciences.
Currently May is conducting collaborative research with the Commonwealth War Graves Commission to investigate new methods of preventing algae from growing on headstones in military cemeteries around the world. The types and distribution of algae on stone have been assessed on First and Second World War graves. Environmentally-friendly methods of reducing algal growth are being researched as the next phase of this project.
Dr. May is currently coordinator for a European consortium investigating ways of treating building materials with microbes using bioremediation (BIOBRUSH). Early collaboration with the Building Research Establishment at Garston helped establish his research in heritage microbiology, especially in relation to damage of historic buildings and monuments by microbes. Now the aim of research is to make microbes work to remove salt damage using biotechnology.
May is also active in environmental research, particularly pollution control by wastewater treatment. His research involves collaboration with the Department of Civil Engineering through the Environmental Engineering Research Group, a multidisciplinary team of scientists and engineers.