title: Lead toxicity in cyanobacterial porphyrin metabolism.
abstract: The effect of Pb2+ on growth, tetrapyrrole photosynthetic pigment content, total free porphyrin, and 5-aminolevulinate dehydratase (ALA-D) activity of a cyanobacterium, Microchaete tenera, and its ability to sequester Pb2+ from the culture medium were studied. Pb2+ was assayed by graphite furnace atomic absorption spectrophotometry. M. tenera growth and chlorophyll a content were not affected by 0.5, 1.0, and 6.0 ppm of Pb2+. These treatments doubled the protein content and increased the phycobiliprotein content by four times after 7 days. The ALA-D activity decreased in all concentrations by 63% at day 7 and by 34% at day 14. As a consequence of ALA-D inhibition, total free porphyrin also decreased by 64% at day 7 and by 40% at day 14. The highest biomass lead uptake (7454 +/- 565 micrograms Pb2+/g dry weight) was observed at day 3 with 6.0 ppm of Pb2+ in the culture medium. Uptake coefficient was highest (3723 +/- 279 micrograms Pb2+ g-1 dry weight/ppm of applied Pb2+) with 1.0 ppm after 3 days. The increase in protein and antenna pigments on day 7 was probably a response to stress conditions and could explain why the toxic metal did not affect growth. ALA-D inhibition and high lead biomass content confirm the importance of this enzyme as a biological indicator for stress.
authors.affiliation: Laboratorio de Fisiología Vegetal y Biología de Cyanobacteria, Pab. II, 4o P, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Intendente Güiraldes 2620 (1428), Buenos Aires, Argentina. cyanob@bg.fcen.uba.ar
authors.forename: M C
authors.initials: MC
authors.lastname: Zaccaro
authors.forename: C
authors.initials: C
authors.lastname: Salazar
authors.forename: G
authors.initials: G
authors.lastname: Zulpa de Caire
authors.forename: M
authors.initials: M
authors.lastname: Storni de Cano
authors.forename: A M
authors.initials: AM
authors.lastname: Stella
mesh_terms: D000458:Cyanobacteria / Q000187:drug effects* / Q000254:growth & development / Q000378:metabolism; D007854:Lead / Q000032:analysis / Q000633:toxicity*; D010788:Photosynthesis; D000623:Porphobilinogen Synthase / Q000378:metabolism; D011166:Porphyrins / Q000378:metabolism*
chemical_list: D011166:Porphyrins; D007854:Lead; D000623:Porphobilinogen Synthase