xii, 153 leaves : / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (M.D.)--University of Adelaide, Dept. of Medicine, 1973

No description available.

No description available.

Large summertime proliferations (or blooms) of the noxious filamentous cyanobacterium Lyngbya majuscula have been observed in the coastal marine waters of Moreton Bay, Queensland. This photosynthetic organism is believed to have a high iron requirement and preliminary studies have shown that the presence of organically complexed iron stimulates growth. Since there is no evidence that Lyngbya produces siderophores to aid iron acquisition, it has been hypothesized that this organism may acquire iron via reduction of ferric complexes to the typically more labile, ferrous form. Both the phylogenetic diversity of the genus Lyngbya and the iron metabolism of L. majuscula are examined in this thesis. Software was developed to assist in the design of peR primers that targeted l6S rRNA, rpoB and Highly Iterated Palindrome (HIP) genetic structures and the subsequent phylogenetic analysis. The mechanism of iron acquisition by L. majuscula and the influence of organic complexation of iron were investigated using radioisotope and chemiluminescence-based techniques. Molecular techniques were also used to investigate the genetics of iron metabolism of L. majuscula. Results of the l6S rRNA analysis indicate that the morpho-genus Lyngbya encompasses a large genetic diversity within the cyanobacteria that is consistent with its reported metabolic and ecological diversity. Five discrete lineages comprised of organisms that fit the morophological definition of Lyngbya were discovered in this analysis. L. majuscula utilises endogenously-produced superoxide as a reductant of ferric complexes to produce the more labile ferrous forms. The nature of the organic complexes has been shown to determine the efficacy of this mechanism. A model of iron acquisition by these reductive processes was developed and was shown to generally describe all known methods of reduction-mediated iron acqUIsItIOn. Finally, the genetics of iron metabolism of L. majuscula was found to be consistent with the mechanism we propose, including the discovery of a component of a ferrous iron uptake mechanism.

Thesis (Ph. D.)--Columbia University. / Vita.

The cyanobacterium Anabaena sp. (PCC #6411) is known to produce the siderophore, schizokinen, in response to iron limitation. Environmental factors which influence schizokinen production have been examined utilizing a bioassay method based upon the stimulation of growth of the siderophore-requiring bacterium Arthrobacter flavescens JG-9. Schizokinen production by Anabaena increased in low-iron media and was stimulated approximately five-fold media containing one millimolar citric acid. Growth of Anabaena under nitrogen-fixing conditions reduced extracellular schizokinen concentrations 3-4 fold, in late growth phase, compared to cells grown on nitrate. Cells grown in ammonium-containing medium yielded intermediate concentrations of schizokinen. The Csaky assay, which is often used to detect hydroxamate siderophores, was found to be subject to interferences that can yield erroneously high values. The problems associated with detection and quantitation of cyanobacterial siderophores are discussed. Anabaena was found to utilize schizokinen to accumulate > 90% of the (('55)Fe)-ferric iron added to the medium. Iron transport capability was increased in iron-starved cells. The transport system appears to be fairly specific for schizokinen, in that an acetylated derivitive of schizokinen, also supported iron transport, but the structurally related siderophore, aerobactin, and the trihydroxamate siderophore, ferrioxamine B, did not support iron uptake by Anabaena. The uptake of ferric schizokinen displayed saturation-type kinetics with an apparent K(,M) of 35 nM, and required the input of metabolic energy. Lightdriven transport was blocked by uncouplers and ATPase inhibitors. Transport in dark-adapted cells was additionally blocked by inhibitors of respiration. We conclude that ATP serves as an energy source for the cellular uptake of schizokinen. Two other kinds of Anabaena were examined for siderophore production. Anabaena sp. (PCC #7120) was found to produce a substance which stimulates the growth of the Arthrobacter JG-9. This substance binds iron and has a similar absorbance maximum to schizokinen in ferric-perchlorate solutions. Anabaena 7120 also utilized ferric schizokinen and ferric acetyl-schizokinen for iron uptake, but not aerobactin or ferrioxamine B. These results suggest that the iron transports systems of Anabaena 6411 and 7120 may be the same. Anabaena cylindrica Lemm. apparently does not produce or utilize a schizokinen-type siderophore. No Arthrobacter JG-9 stimulating material could be detected in low-iron filtrates, even if concentrated 25-fold.

published_or_final_version / abstract / Chemistry / Doctoral / Doctor of Philosophy

No description available.

No description available.

In addition to nitrogen and phosphorus, iron is an essential nutrient for oceanic primary productivity. Unlike nitrogen and phosphorus however, negligible amounts of iron are supplied to surface waters through recycling or mixing but instead from the limited and sporadic input of aeolian particulate. The low concentration of iron that becomes biologically available from the dust places a serious constraint on the heavily iron-dependent processes of photosynthesis and nitrate reduction which affect primary productivity. As much as 47% of the total oceanic primary productivity can be attributed to cyanobacteria making them critical organisms in the biogeochemical cycles. This thesis addresses the effect of iron on primary productivity using a combined approach of physiological and molecular biology. The physiological response of three marine strains of Synechococcus to growth on different concentrations of FeEDTA was investigated. Cells grown with higher concentrations of iron had greater cell density, more Chl- and phycobiliproteins and higher carbon fixation rates than cells grown at limiting iron concentrations (l0-8 M Fe). Iron enrichment of iron limited cultures stimulated carbon fixation, growth rate, and pigment and protein synthesis. Iron limited cells spiked with SJ.l.M Nlf4Cl prior to short term incubations had higher dark carbon fixation than cells gro·wn at higher iron and also spiked to 5J.1M Nlf4Cl. The addition of ammonium relieves a restricted nitrogen assimilatory pathway in the low iron cells that is evidenced by increased dark carbon fixation. We propose that this measurement of enhanced dark carbon fixation could be a useful assay in supporting the contention that populations of Synechococcus in nitrate rich waters are iron limited. Molecular genetic techniques were used to look for the presence of an iron uptake gene in cyanobacteria. Preliminary results indicate that there is a gene that is homologous to the ferric uptake regulation (fur) gene in E. coli. This hybridization occurred in siderophore-producing cyanobacteria, but not in marine cyanobacteria that do not produce siderophores. The fact that marine Synechococcus do not produce siderophores and did not hybridize to the fur gene suggest that fundamentally different mechanisms for iron uptake operate in high biomass freshwater cyanobacteria and cyanobacteria from dilute oligotrophic waters.