The Growth of Streptomycetes and Fungi Under Controlled Conditions on the Surface of Coated Materials

Abstract

The work presented is an investigation into some factors effecting the commercial testing of cotton textiles. Soil burial is the standard test for microbial biodeterioration of materials and evaluation of biocides used to protect them, but is extremely variable. Pure culture techniques were employed to evaluate two factors, moisture availability and the action of Streptomycetes (particularly Streptomyces spp. ), which might lead to variability. Present methods for controlling and monitoring relative humidity in the laboratory had disadvantages, and so novel methods for producing and measuring such atmospheres were developed. A continuous wet/dry air mixing system was designed and constructed to give a controlled humidity environment, allowing fungal and streptomycete colonisation of wheat starch and cellulose substrates to be studied. The apparatus permitted simultaneous production of seven humidities and avoided a decrease in the oxygen-carbon dioxide ratio, giving conditions more akin to those encountered during the service life of a textile. A dual p.n.p. bismuth-telluride thermocouple hygrometer was devised capable of monitoring the relative humidities of the air mixing system. Gravity plate airspora isolations of Streptomyces spp. were performed in conjunction with fungal isolations, to assess the potential biodeterioration threat presented by mesophilic Streptomyces spp. Streptomyces spp. isolated were tested for amylolytic and cellulolytic ability, pH and temperature growth limits. Moisture requirements of Streptomyces spp. were determined using three methods; air mixing, saturated salt solutions and controlled water activity agar. Having established the limits within which Streptomyces spp. were capable of starch and cellulose degradation they were tested on starch coated cotton textiles. Sized textiles protected by one of three biocides; sodium pentachlorophenol, tributyltin oxide or salicylanilide, were evaluated under controlled conditions. Estimation of biocide efficiency and Streptomyces spp. tolerance were determined visually and by tensile strength testing of inoculated textile strips.