The significance of appropriate sampling and cultivation techniques in the effective assessment of biodeterioration
(Sponsored by ENGLISH HERITAGE)
In order to understand the mechanisms of microbial aggression, microbiologists have aimed to isolate organisms from their original environment and cultivate them in vitro. This approach has limitations: sampling and cultivation are processes that exert selective influences on organisms removed from their original environment. In addition, many organisms may not be cultivatable
if the appropriate nutritional and environmental conditions are not provided. Consequently, a complete image of the dynamic and complex nature of biodeterioration is extremely difficult to establish.
The present research has involved a review of the microbiological methods currently used for the sampling of organisms from cultural material. Using the biodeterioration of the Romanesque wall paintings at Hardham Church (West Sussex) as an investigative case study, a variety of techniques used for sampling÷brushes, direct agar, fragment, loop, needle, swab, tape and velvet÷were assessed for their ability to collect a representative sample of viable organisms.
Further investigations aimed to cultivate the sampled organisms on a variety of media, so that the effects of variations in the type of medium could be assessed. In an attempt to replicate the nutritional conditions of the painted wall, a ‘Hardham wall salts’ medium was developed. It was found that pigmented organisms were more likely to grow on a minimal salts medium (Pseudomonas basal medium) containing all elements essential for growth in specific quantities.
Pigmented organisms isolated for subsequent stages of investigation were identified by gram-stains and api test systems. A range of gram-negative Pseudomonas-like species displaying a diverse range of metabolic activity were revealed. Stock cultures of the organisms of interest were made, and finally the influence of temperature and relative humidity on the growth of isolated pigmented organisms was examined. It was found that reduction in temperature caused a decrease in the growth and development of organisms, and that the pigmentation phenomenon developed over the period of cultivation with an increase in cell mass. Variation in relative humidity did not yield useful results since the variable was swamped by the available moisture in the nutrient media.
Recent advances in molecular biology have provided new tools for microbiological investigations÷such as PCR÷that may overcome the limitations associated with traditional methods of sampling and cultivation. However, many of these methods are intended to identify the species associated with biodeterioration rather than to investigate the mechanisms of microbiological decay. At present, sampling and cultivation to produce a stock culture remains the most feasible method of assessing microbiological activity, despite its limitations. However, a combination of molecular and microbiological methods may soon provide the best approach to understanding the mechanisms of biodeterioration.