Effect of Support Material on the Development of Microbial Fixed Films Converting Acetic Acid to Methane*

A study of the development of methanogenic fixed films on pieces of polyvinyl chloride plastic, etched glass and baked clay showed that support material markedly affected the rate of attachment and growth of bacteria converting acetic acid to methane. Film development, as indicated by the rate of acetate conversion to methane and carbon dioxide, was threefold faster on fired clay than on either PVC plastic or etched glass. Scanning electron micrographs showed that the film of bacteria attached to clay was thick and uniform, while the film attached to PVC plastic was thin although still uniform. Attachment to etched glass was spotty. The characteristics of clay which made it a superior support appeared to be its rough, porous surface which offered attachment sites to the micro-organisms and the presence of minerals in the clay, particularly iron which is known to stimulate methanogenesis and growth.     

The measurement of multiple spray deposits by sequential application of metal chelate tracers

Chelates of the transition metals copper, cobalt, manganese and zinc, available as foliar feeds, were identified as the most suitable spray tracers for comparisons of deposits arising from up to four sequential applications to a single target. Their use minimised many of the disadvantages associated with other commonly used tracers such as visible and fluorescent dyes, and it was possible to quantify each tracer when present on the target in ratios of up to 100:1. Each spray solution contained a single chelate at a metal concentration of 1 g litre^?1. The recovery of metal chelates from plant tissue may not be quantitative, as a consequence of absorption or adsorption by leaves for example. The food colorant tartrazine, at a concentration of 10 g litre^?1, was shown to be a suitable internal standard for estimation of percentage recovery. Combined spray deposits were recovered readily from apple leaves and fruit by aqueous extraction and analysed by atomic absorption spectroscopy. The spray deposit of each metal tracer was calculated from the raw analytical data using procedures for generating calibration curves designed to optimise the accuracy of the analysis.     

A Cell Culture System for Study of the Development of Toxoplasma gondii Bradyzoites

ABSTRACT. Toxoplasma gondii is a ubiquitous apicomplexan parasite and a major opportunistic pathogen under AIDS-induced conditions, where it causes encephalitis when the bradyzoite (cyst) stage is reactivated. A bradyzoite-specific Mab, 74.1.8, reacting with a 28 kDa antigen, was used to study bradyzoite development in vitro by immuno-electron microscopy and immunofluorescence in human fibroblasts infected with ME49 strain T. gondii . Bradyzoites were detected in tissue culture within 3 days of infection. Free floating cyst-like structures were also identified. Western blotting demonstrated the expression of bradyzoite antigens in these free-floating cysts as well as in the monolayer. Bradyzoite development was increased by using media adjusted to pH 6.8 or 8.2. The addition of γ-interferon at day 3 of culture while decreasing the total number of cysts formed prevented tachyzoite overgrowth and enabled study of in vitro bradyzoites for up to 25 days. The addition of IL-6 increased the number of cysts released into the medium and increased the number of cysts formed at pH 7.2. Confirmation of bradyzoite development in vitro was provided by electron microscopy. It is possible that the induction of an acute phase response in the host cell may be important for bradyzoite differentiation. This system should allow further studies on the effect of various agents on the development of bradyzoites.