Abstract
The genus Prochlorothrix gen., with one species, Prochlorothrix hollandica sp. nov., is proposed for filamentous oxygenic photoautotrophic procaryotes containing chlorophylls a and b. The cylindrical cells are arranged in trichomes which lack sheaths, are not motile, and do not possess differentiated cells. P. hollandica grows in liquid media or on solid mineral media and is incapable of dinitrogen fixation. Optimum growth occurs between 20 and 30°C and at pH 8.4. The deoxyribonucleic acid base composition of this organism is 53 mol% guanine plus cytosine. Emendation of the description of the order Prochlorales Florenzano, Balloni, and Materassi 1986 is proposed since the original definition of this taxon would exclude the genus Prochlorothrix. To accommodate the filamentous genera in the order Prochlorales. we propose the family Prochlorotrichaceae fam. nov.