Transformation of vivianite by anaerobic nitrate-reducing iron-oxidizing bacteria

In phosphate-rich environments, vivianite (Fe^II₃(PO₄)₂, 8H₂O) is an important sink for dissolved Fe(II) and is considered as a very stable mineral due to its low solubility at neutral pH. In the present study, we report the mineralogical transformation of vivianite in cultures of the nitrate-reducing iron-oxidizing bacterial strain BoFeN1 in the presence of dissolved Fe(II). Vivianite was first transformed into a greenish phase consisting mostly of an amorphous mixed valence Fe-phosphate. This precipitate became progressively orange and the final product of iron oxidation consisted of an amorphous Fe(III)-phosphate. The sub-micrometer analysis by scanning transmission X-ray microscopy of the iron redox state in samples collected at different stages of the culture indicated that iron was progressively oxidized at the contact of the bacteria and at a distance from the cells in extracellular minerals. Iron oxidation in the extracellular minerals was delayed by a few days compared with cell-associated Fe-minerals. This led to strong differences of Fe redox in between these two types of minerals and finally to local heterogeneities of redox within the sample. In the absence of dissolved Fe(II), vivianite was not significantly transformed by BoFeN1. Whereas Fe(II) oxidation at the cell contact is most probably directly catalyzed by the bacteria, vivianite transformation at a distance from the cells might result from oxidation by nitrite. In addition, processes leading to the export of Fe(III) from bacterial oxidation sites to extracellular minerals are discussed including some involving colloids observed by cryo-transmission electron microscopy in the culture medium.     

Development of simple sequence repeat markers for Botryosphaeria spp. with Fusicoccum anamorphs

We report the development of eight sets of microsatellite markers for the ascomycete fungus and tree pathogen, Botryosphaeria parva. The primers were identified after cloning and sequencing of fragments amplified using simple sequence repeat (SSR) primers. Genome walking was used to determine unknown sequences on either side of new SSRs. The primers were tested and proved useful in nine other Botryosphaeria species that all have Fusicoccum anamorphs, similar to B. parva.     

MATING SYSTEM ANALYSIS USING PROTEIN ELECTROPHORESIS IN THE SELF-FERTILE HERMAPHRODITE SPECIES BULINUS TRUNCATUS (GASTROPODA: PLANORBIDAE)

Uniparental reproduction in the tetraploid hermaphrodite speciesBulinus truncatus has been suggested to occur via self-fertilization,on the basis of cytological and genetic studies. However, recentanalyses of population genetic structure by protein electrophoresisindicated the occurrence of multi-banded phenotypes referredto as ‘fixed hetero-zygosity’. Although intrapopulationand geographical variation of multibanded phenotypes occur,many populations bear only one type of such patterns. This ledto the suggestion that parthenogenesis may well be the matingsyste in B. truncatus. However, such fixed heterozygosity patternsare expected in some tetraploid species in which double disomicinheritance of alleles occurs. It is therefore not possibleto determine from population genetic structure analysis alonewhether segregation occurs or not. Here, we investigate thestability of such patterns over one generation of uniparentalreproduction among four populations. We also present resultsof crossing experiments between individuals from two populations,using two diagnostic loci to analyse their offspring. Our resultsclearly indicate Mendelian segregation of alleles, and confirmsexual reproduction by self-fertilization and cross-fertilization.We interpret the multibanded patterns observed in populationsas the product of both diploid loci of the tetraploid genomewhen they are monomorphic for different alleles. Our study alsoallows us to suggest that partial selfing may be the regularmating system in B. truncatus. (Received 12 February 1992; accepted 7 September 1992)     

Symbiotic Performance of Supernoclulating Soybean (Glycine max (L.) Merrill) Mutants during Development on Different Nitrogen Regimes

Growth and symbiotic performance of soybean (Glycine max (L.)Merrill) cv. Bragg and three of its induced nodulation mutants(nod49, non-nodulating; ntsl 116, intermediate supernodulator;nts1007, extreme supernodulator) were compared throughout developmentunder different nitrogen regimes (0, 2, 5 and 10 mol nitratem^–3). Nitrogen fixation was assessed using ¹⁵N-isotopedilution and xylem sap analysis for ureide content. Both techniquesconfirmed a complete lack of N₂ fixation activity in nod49.Plant reliance on nitrogen fixation by the other genotypes wasdependent on the nitrate regime and the developmental stage.The ntsl007 and ntsl 116 mutants fixed more nitrogen than theparent cultivar in the presence of 10 mol m^–3 nitratein the nutrient solution, but higher input of symbioticallyderived nitrogen was still insufficient to offset the amountof nitrogen removed in the harvested seed. However, the mutantsutilized less nitrate for growth than Bragg. Comparison of estimatesof N₂ fixation derived from the ¹⁵N-dilution technique withthose based on relative ureide content of xylem sap indicatedthat the latter offered a simple and reliable procedure forevaluating the symbiotic performance of supernodulating plants. Key words: ¹⁵N-isotope dilution, supernodulation, ureides