Cellulose-synthesizing machinery in bacteria

Cellulose - Cellulose is produced by all plants and a number of other organisms, including bacteria. The most representative cellulose-producing bacterial species is Gluconacetobacter xylinus, an...     

Preparation,X-ray crystallography,and thermolysis of phenylenediammonium dibromide salts

Phenylenediammonium dibromide (PDADBr) salts have been prepared and characterized by X-ray crystallography. The thermal decomposition of PDADBr has been studied by thermogravimetry (TG) and differential thermal analysis (DTA). Kinetic parameters have been evaluated using model fitting and isoconversional methods. The thermolytic pathways have also been suggested which involve proton transfer as a primary step to regenerate parent amine and HBr. Interaction between amine and HBr at higher temperature yields gaseous products.     

Isolation and characterization of the cellulose synthase genes <Emphasis Type="Italic">PpCesA6</Emphasis> and <Emphasis Type="Italic">PpCesA7</Emphasis> in <Emphasis Type="Italic">Physcomitrella patens</Emphasis>

Analysis of cellulose biosynthesis using molecular approaches has been successful in identifying genes in many cellulose-producing organisms, yet the mechanism of cellulose biosynthesis still remains to be understood. We are interested in developing the moss Physcomitrella patens as a useful system for the study of cellulose biosynthesis. This moss affords a number of advantages including a haploid dominated gametophyte and a very high efficiency of homologous recombination in its nuclear DNA for constructing gene knockouts. In addition, P. patens has only a primary cell wall unlike Arabidopsis thaliana, which has both a primary and a secondary cell wall. We identified two full-length cellulose synthase (CesA) genes of P. patens, PpCesA6 and PpCesA7 from an EST database and have analyzed the genomic sequences. PpCesA6 and PpCesA7 show high similarity to each other, both at the cDNA and genomic DNA levels. Single and double knockouts of PpCesA6 and PpCesA7 were generated and screened for phenotypic changes. While the PpCesA6 and PpCesA7 single knockouts did not show any obvious phenotypic differences from the wild-type, the double knockout had significantly reduced stem length. These results suggest that PpCesA6 and PpCesA7 probably have a very similar role in cellulose biosynthesis and their functions may be redundant. Additionally, their roles may overlap with the other P. patens CesAs as observed for CesAs involved in primary cell wall biosynthesis in A. thaliana.     

Bulk ablation of soft tissue with intense ultrasound: modeling and experiments

Methods for the bulk ablation of soft tissue using intense ultrasound, with potential applications in the thermal treatment of focal tumors, are presented. An approximate analytic model for bulk ablation predicts the progress of ablation based on tissue properties, spatially averaged ultrasonic heat deposition, and perfusion. The approximate model allows the prediction of threshold acoustic powers required for ablation in vivo as well as the comparison of cases with different starting temperatures and perfusion characteristics, such as typical in vivo and ex vivo experiments. In a full three-dimensional numerical model, heat deposition from array transducers is computed using the Fresnel approximation and heat transfer in tissue is computed by finite differences, accounting for heating changes caused by boiling and thermal dose-dependent absorption. Similar ablation trends due to perfusion effects are predicted by both the simple analytic model and the full numerical model. Comparisons with experimental results show the efficacy of both models in predicting tissue ablation effects. Phenomena illustrated by the simulations and experiments include power thresholds for in vivo ablation, differences between in vivo and ex vivo lesioning for comparable source conditions, the effect of tissue boiling and absorption changes on ablation depth, and the performance of a continuous rotational scanning method suitable for interstitial bulk ablation of soft tissue.