HETEROTROPHISM AND SPECIES CONCEPTS IN BEGGIATOA

From a variety of localities 14 strains of Beggiatoa, 1 ¼–3μ wide, were isolated in axenic heterotrophic culture. Most of these were freshwater forms, 2 were from brackish water, 1 was marine. The widths of the individual strains were constant, independent of conditions. The nutritional requirements of most of the strains are simple. Acetate at low concentrations, an ammonium salt as nitrogen source and the usual inorganic salts including trace elements supported growth. A few strains did not grow well without addition of an amino acid, and 2 (identical) strains required peptone or beef extract. Lactate, succinate, or pyruvate could often replace acetate. Multiplication was in most cases also possible with amino acids alone, without a further organic substrate. The appearance of the various strains on agar plates differs characteristically. Two types could be discerned: one forms spirals and one grows in tongues. These 2 types are not homogeneous for there are within them differences in width, growth rate, nutrition, and salt tolerance, so that a considerable number of independent forms exist even within the narrow limits in width of trichomes to which the investigations were restricted.     

Copper- and arsenate-induced oxidative stress in Holcus lanatus L. clones with differential sensitivity

The biochemical responses of Holcus lanatus L. to copper and arsenate exposure were investigated in arsenate‐tolerant and ‐non‐tolerant plants from uncontaminated and arsenic/copper‐contaminated sites. Increases in lipid peroxidation, superoxide dismutase (SOD) activity and phytochelatin (PC) production were correlated with increasing copper and arsenate exposure. In addition, significant differences in biochemical responses were observed between arsenate‐tolerant and ‐non‐tolerant plants. Copper and arsenate exposure led to the production of reactive oxygen species, resulting in significant lipid peroxidation in non‐tolerant plants. However, SOD activity was suppressed upon metal exposure, possibly due to interference with metallo‐enzymes. It was concluded that in non‐tolerant plants, rapid arsenate influx resulted in PC production, glutathione depletion and lipid peroxidation. This process would also occur in tolerant plants, but by decreasing the rate of influx, they were able to maintain their constitutive functions, detoxify the metals though PC production and quench reactive oxygen species by SOD activity.