Conformation of poly(γ-glutamic acid) in aqueous solution.

Local conformation and overall conformation of poly(γ-DL-glutamic acid) (PγDLGA) and poly(γ-L-glutamic acid) (PγLGA) in aqueous solution was studied as a function of degree of ionization ε by (1) H-NMR, circular dichroism, and potentiometric titration. It was clarified that their local conformation is represented by random coil over an entire ε range and their overall conformation is represented by expanded random-coil in a range of ε > ε(*) , where ε(*) is about 0.3, 0.35, 0.45, and 0.5 for added-salt concentration of 0.02M, 0.05M, 0.1M, and 0.2M, respectively. In a range of ε < ε(*) , however, ε dependence of their overall conformation is significantly differentiated from each other. PγDLGA tends to aggregate intramolecularly and/or intermolecularly with decreasing ε, but PγLGA still behaves as expanded random-coil. It is speculated that spatial arrangement of adjacent carboxyl groups along the backbone chain essentially affects the overall conformation of PγGA in acidic media.

Analysis of ammonia monooxygenase and archaeal 16S rRNA gene fragments in nitrifying acid-sulfate soil microcosms.

The present study describes the occurrence of a unique archaeal ammonia monooxygenase alpha subunit (amoA) gene in nitrifying acid-sulfate soil microcosms at pH 3.5. The soil was collected from an abandoned paddy field in Thailand. Microcosms were incubated in the dark at 30°C for 372 days with the following three treatments: addition of ammonium sulfate solution once a month (I) or once a week (II), and addition of only sterilized water (III). A quantitative PCR analysis revealed an increase in abundance of the archaeal amoA gene in microcosm soils in which nitrate concentrations increased after incubation. A phylogenetic analysis indicated a predominance of the novel gene, and a predominance of a betaproteobacterial amoA gene affiliated with the genus Nitrosospira. A 16S rRNA gene-based PCR assay revealed that crenarchaeotic Group I.1d was predominant among the Crenarchaeota in microcosms. These results suggest the presence of ammonia-oxidizing archaea corresponding to the unique amoA lineage in nitrifying acid-sulfate soil microcosms at pH 3.5.