Paraquat dichloride (l,l'-dimethyI-4,4'-bipyridylium dichloride) induced the production of the hydrocarbon gases propane, ethane and ethylene in the xanthophycean microalga Burnilleriopsis filiforrnis. Formation of these gases was dependent on the light intensity and photosynthetic electron transport. Diquat dibromide (1 ,l'ethylene-2,2'-bipyridylium dibromide), having a higher midpoint potential than paraquat dichloride, induced an even higher evolution of the gases. A total lack of oxygen inhibited the production of gas, while a low oxygen concentration ( 4 6 % by volume) stimulated paraquat-induced gas formation. Culturing algae autotrophically, in a medium with a higher iron content, also increased the production of gases in the presence of the herbicide. Formation of these gases is an indication of the peroxidation of membrane lipids which, according to previous results, is correlated with a decrease of photosynthetic electron-transport activity.
Physiological and Biochemical Contributions to the Taxonomy of the Genus Chlorella VIII. The Base Composition of DNA Summary. The base composition of the DNA isolated from 88 strains of the genus Chlorella was found to show large differences. The GC content is between 43 and 79~ In most cases, however, there is very little variation between different strains of the same taxon. Thus the base composition of DNA can serve as a valuable taxonomic character. Chlorella vulgaris/, tertia, which contains hydrogenase and is thermophilic, can be clearly separated from the morphologically identical C. vulgaris var.vulgaris. The significance of a few cases of considerable differences between otherwise physiological]y and morphologically identical strains in the base composition of their DNA is discussed. It might indicate a beginning tendency towards the formation of new taxa.Zusammen/assung. Die Basenzusammensetzung der DNS yon 88 Chlorella-St~mmen weist sehr grol3e Unterschiede auL Der GC-Gehalt liegt im Bereich yon 43--79~ Die verschiedenen St~mme eines Taxons zeigen jedoch im allgemeinen nur sehr geringe Differenzen, so dab sich die Basenzusammensetzung der DNS als wertvolles taxonomisches Merkmal erweist. Chlorella vulgaris/, tertia, die sich durch das Vorhandensein yon Hydrogenase und Thermophilie yon der morphologisch gleichen C.vulgaris var.vulgaris unterscheidet, kann auch hier klar abgegrenzt werden. Die Bedeutung einiger Abweichungen bei sonst physiologisch: biochemisch und morphologisch-cytologisch einheitlichen St~mmen wird diskutiert. MSglicherweise handelt es sich dabei um ein erstes Anzeichen fiir die beginnende Herausbildung neuer Taxa.Aufgrund physiologisch-bioehemischer Merkmale erscheint es sinnroll, die Gattung Chlorella in 11 Taxa einzuteilen (Kessler, 1967(Kessler, , 1972bKessler et al., 1968; Kessler u. Zweier, 1971). Diese Taxa wurden yon Fott u. Novs163 (1969) auch morphologisch-cytologisch bearbeitet und best~tigt. Eine taxometrische Behandlung der Gattung Chlorella (mit Ausnahme yon C. fusca vat. rubescens), unter Berfieksichtigung der 21 Arch. Microbiol., Vol. 95
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