Characterization of the Elasticity of Small Objects Buried in Media Based on the Measurements of Photoacoustic Temporal Waveforms.

Since the elasticity of biological tissues is related to their pathological states, the development of new methods allowing for non-invasive measurements of the elasticity has been desired in the medical field. We present a characterization of the elasticity of objects buried in media from the temporal waveforms of photoacoustic signals. As the increment in Young's moduli of the objects, the frequency corresponding to the gravitational center of the power spectra obtained by the Fourier-transformation of the waveforms is increased. In our experiment configuration, the elasticity of buried objects is able to be identified up to about 1 MPa of Young's modulus from the frequency. These results suggest that measurements on the temporal waveforms of photoacoustic signals and the resultant power spectra would provide a useful method for evaluating the elasticity of deeply-situated microscopic pathological lesions, such as stage 0 or 1 mammary gland cancer, which is difficult by conventional ultrasound elastography.

A novel aerobactin utilization cluster in Vibrio vulnificus with a gene involved in the transcription regulation of the iutA homologue.

We demonstrated that Vibrio vulnificus M2799 utilizes aerobactin for growth as an exogenous siderophore under iron-limiting conditions, concomitant with enhanced production of the 76-kDa iron-repressible outer membrane protein. Subsequently, by applying the Fur titration assay method to the M2799 genomic libraries followed by further cloning of the regions surrounding the candidate genes, we identified the 8.4-kb aerobactin utilization gene cluster which consists of five genes arranged in three distinct transcriptional units. It was confirmed by disruption of the corresponding genes that the first unit forming a three-gene operon (vatCDB) and the third unit of a single gene (iutA) encode an ATP-binding cassette transport component and the 76-kDa ferric aerobactin receptor, respectively. The second unit of another single gene (iutR), encodes a homologue of the GntR family of transcriptional repressors. Although transcription of the first and third units was iron-regulated, the iutR gene was transcribed regardless of iron status in the growth medium. Construction of an iutR disruptant coupled with genetic complementation experiments suggested that the gene encodes a transcriptional repressor for iutA. This is the first example of a regulator gene involved in aerobactin-enhanced production of IutA.

Identification of an AraC-like regulator gene required for induction of the 78-kDa ferrioxamine B receptor in Vibrio vulnificus.

We previously reported that the 78-kDa outer membrane receptor for ferrioxamine B is induced in iron-starved Vibrio vulnificus cells when desferrioxamine B was supplied exogenously. Based on its N-terminal amino acid sequence, a candidate gene for the ferrichrome B receptor was detected in the V. vulnificus CMCP6 genomic database. Here, two contiguous genes, named desR and desA, encoding a member of the AraC family of transcriptional activators and the ferrioxamine B receptor, respectively, were cloned from V. vulnificus M2799 and characterized. Primer extension analysis mapped the iron-regulated transcription initiation sites for desR and desA, and demonstrated involvement of desferrioxamine B in the induction of desA transcription. Insertion mutation of desR resulted in no production of DesA under iron-limiting conditions even in the presence of desferrioxamine B. The DesA production under the same conditions was restored to wild-type levels when the desR mutant was complemented with desR in trans. These results suggest that the desR gene is required for desferrioxamine B-inducible production of DesA in iron-starved cells.