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Frankia sequences that have RNA polymerase promoter activity have been studied. Fragments of Frankia strain Arl6 genomic DNA were cloned upstream of a promoterless, Vibrio harveyi lux AB cassette to isolate a section of the DNA that acts as an RNA polymerase promoter. Frankia may use mechanisms similar to those of the enteric bacteria and rhizobia in the expression of nitrogen-regulated genes. A cloned Frankia DNA that directs initiation of transcription in a Frankia cell-free extract from two promoter regions was identified. The upstream promoter, TSP-1, has sequences like those in the canonical Escherichia coli promoter and a Streptomyces promoter element. Frankia are Gram-positive, filamentous pioneer species and are able to fix atmospheric dinitrigen in the free-living state or in symbiosis with various woody plants.

Diffuser fouling is classified as one of three types, A, B, and C, based on the nature of the foulant. The accumulation of inorganic foulants, such as fine particles and precipitates, characterize type A fouling, and the formation of biomass characterize type B fouling. Type C fouling is characterized by the formation of biofilm, fortified by the entrapment of inorganic particles within the biomass. Hypotheses were developed to describe the mechanisms of dynamic change in diffuser operating performance as a result of the three different types of diffuser fouling. The hypotheses specific to each type were evaluated by testing the appropriate hypothetical equations using the data produced in this study. Results indicate that the physical properties of the biofilm are important factors in fouling, causing a significant change in diffuser characteristics. Entrapment of inorganic particles, such as sands, within the biofilm, significantly increase the dynamic wet pressure (DWP) and alter the bubble size. The association between DWP and bubble size could be quantitatively described by a hypothetical fouling equation for the three different types of fouling in these laboratory studies.