| Abstract: High concentrations of nitrite in molasses of an Austrian sugar factory gave a rise to a systematic survey in order to identify location and cause of the formation of nitrite. The high levels could only partially be explained by microbial reduction of nitrate in the diffusion plant. It turned out that the critical rise of nitrite occurred during the passage of thin juice through a newly installed softening plant. Careful inspection of the plant revealed massive bacterial films on the gravel bed of the ion exchange columns, although the temperature of the thin juice in the exchange columns had been kept at 80°C, thus exceeding the temperature tolerance limit of thermophilic, sporulating bacteria. However, cultivation of the mixed population of isolated bacteria in the laboratory confirmed their ability to reduce nitrate at 80°C. Upon growth in single cell colonies and both physiological and microscopical examination their affiliation to the genus Thermus was shown, which represents an extremely thermophilic, non-sporulating group of Gram-negative bacteria. These results mean that in sugar factories bacterial activity has to be taken into account also in such sectors which hitherto have been regarded as non-critical.
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