Submitted to: Brazilian Journal of Microbiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/7/2003
Publication Date: 6/1/2003
Citation: Fukushima, R.S., Weimer, P.J., Kunz, D. 2003. Use of photocatalytic reduction to hasten preparation of culture media for saccharolytic clostridium species. Brazilian Journal of Microbiology. 34:22-26. Interpretive Summary: The genus Clostridium includes a variety of bacterial species of medical, veterinary, and agricultural importance. Cultivation of these strictly anaerobic bacteria in the laboratory is simplified by including cysteine (or other chemical reducing agent) in the culture medium to remove oxygen, along with resazurin, an indicator of whether or not the medium is anaerobic (oxygen-free). We have simplified the process for preparing culture media for growth of Clostridium species by exposure of such media to high intensity light, which promotes a light-catalyzed reaction to hasten the onset of anaerobic conditions, such that the culture medium can be used immediately after its preparation. In terms of its ability to support Clostridium growth, medium reduced under high light intensity is identical to that prepared under normal light conditions. The modified method of medium preparation saves time and labor, improving the laboratory efficiency.
Technical Abstract: Cysteine is the preferred reducing agent used in the preparation of culture media for the growth of many strictly anaerobic microorganisms; however, redox potential reduction under cysteine is very slow, making it inconvenient if the medium is needed immediately or in large quantity. Time required to reduce culture medium containing resazurin (an indicator of reducing conditions) was dramatically shortened when the medium, after being injected with the reducing agent cysteine, was irradiated with incandescent light from a halogen lamp. Light intensity had an effect upon time to reduce; tubes kept in the dark took more than 12 h to achieve the desired degree of anaerobiosis (measured spectrophotometrically by the bleaching of the indicator, resazurin) while tubes subjected to ordinary laboratory illumination were reduced in about 2 h. When exposed to maximum light intensity (equivalent to a regular 100 watts bulb lamp) tubes could be made anaerobic in less than 20 min. Cysteine was essential for the bleaching of resazurin and evidence that adequate anaerobiosis was achieved by light irradiation was provided by the fact that four Clostridium strains and one Thermoanaerobacter strain displayed similar growth (measured by lag time, growth rate, and extent of growth) in media reduced under high intensity light or under normal laboratory illumination.