Reference Work Entry

The Prokaryotes

pp 115-140

The Genus Azospirillum

  • Anton Hartmann
  • , Jose Ivo Baldani

Historical Aspects

The growth of a spirillum-like bacterium in nitrogen deficient malate- or lactate-based media, which had been inoculated heavily with garden soil, was first observed by Beijerinck in 1922. In contrast to carbohydrate-based media, organic acid-based media supported growth of the spirillum without overgrowth by other nitrogen-fixing bacteria like Azotobacter and Clostridium. Beijerinck found that partially purified cultures of the spirillum exhibited increases in nitrogen at the expense of malate, whereas cultures lacking the spirillum failed to show such increases. In general, cells cultured in sugar media were plump, curved rods containing many lipoidal droplets which sometimes distorted the shape of the cells. On malate or lactate agar, the cells tended to be thinner and straighter, while in dilute bouillon they had a distinct spirillum shape with one or more helical turns. Because of the ease of cultivation on salts of organic acids, as well as the ...

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