Biomedical subjects

K Sudesh

Publications and source records attributed to K Sudesh.

4 recordsLinked to original sources

PubMed2004

Microbial polyhydroxyalkanoates (PHAs): an emerging biomaterial for tissue engineering and therapeutic applications.

Among the various biomaterials available for tissue engineering and therapeutic applications, microbial polyhydroxyalkanoates (PHAs) offer the most diverse range of thermal and mechanical properties. Of particular interest are the PHAs that contain 4-hydroxybutyrate such as poly(3-hydroxybutyrate-co-4-hydroxybutyrate) [P(3HB-co-4HB) and poly(4-hydroxybutyrate) [P(4HB)]. These polyesters can only be synthesized by a few types of bacteria, among which Comamonas acidovorans has the most efficient metabolic pathways to channel 4HB monomers. The resulting polyesters are bioabsorbable and are being developed as a new biomaterial for medical applications. By controlling the molar ratio of the monomers, it is possible to produce materials that are as tough and elastic as rubber.

3-Hydroxybutyric Acid↗

PubMed2000

Factors affecting the freeze-fracture morphology of in vivo polyhydroxyalkanoate granules.

Interesting morphologies were observed when Comamonas acidovorans containing polyhydroxyalkanoates (PHA) of various compositions was freeze-fractured at temperatures far below the glass transition temperatures of PHA. In vivo granules of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) comparatively showed the most ductility, and could be stretched extensively. Contrary to the uniform needle-type deformation shown by the poly(3-hydroxybutyrate) homopolymer when fractured at -110 degrees C, copolymers containing 3-hydroxyvalerate units showed various deformation structures. Similar observations were made when in vivo granules of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) were freeze-fractured, although the ductility of the latter was much reduced. In addition, it was found that fracturing at -160 degrees C resulted in decreased ductility of the PHA granules with the concomitant increase in the number of mushroom-type deformation structures. Our results suggest that PHA granules with higher resistance to freeze-fracture deformation show less ductility, and therefore produce the mushroom-type morphology. This is the first report on the freeze-fracture morphology of PHA copolymers containing short-chain-length monomers.

Cupriavidus necator↗

PubMed1998

Genetic analysis of Comamonas acidovorans polyhydroxyalkanoate synthase and factors affecting the incorporation of 4-hydroxybutyrate monomer.

The polyhydroxyalkanoate (PHA) synthase gene of Comamonas acidovorans DS-17 (phaCCa) was cloned by using the synthase gene of Alcaligenes eutrophus as a heterologous hybridization probe. Complete sequencing of a 4.0-kbp SmaI-HindIII (SH40) subfragment revealed the presence of a 1,893-bp PHA synthase coding region which was followed by a 1,182-bp beta-ketothiolase gene (phaACa). Both the translated products of these genes showed significant identity, 51.1 and 74.2%, respectively, to the primary structures of the products of the corresponding genes in A. eutrophus. The arrangement of PHA biosynthesis genes in C. acidovorans was also similar to that in A. eutrophus except that the third gene, phaB, coding for acetoacetyl-coenzyme A reductase, was not found in the region downstream of phaACa. The cloned fragment complemented a PHA-negative mutant of A. eutrophus, PHB-4, resulting in poly-3-hydroxybutyrate accumulation of up to 73% of the dry cell weight when fructose was the carbon source. The heterologous expression enabled the incorporation of 4-hydroxybutyrate (4HB) and 3-hydroxyvalerate monomers. The PHA synthase of C. acidovorans does not appear to show any preference for 4-hydroxybutyryl-coenzyme A as a substrate. This leads to the suggestion that in C. acidovorans, it is the metabolic pathway, and not the specificity of the organism's PHA synthase, that drives the incorporation of 4HB monomers, resulting in the efficient accumulation of PHA with a high 4HB content.

Acetyl-CoA C-Acyltransferase↗

PubMedDate not supplied

Improved production of poly(4-hydroxybutyrate) by Comamonas acidovorans and its freeze-fracture morphology.

Production of poly(4-hydroxybutyrate) [P(4HB)] by Comamonas acidovorans JCM10181 was studied by introducing additional copies of its PHA synthase gene and the beta-ketothiolase gene. A multi-copy-number broad-host-range plasmid vector, pJRD215, was modified to contain the strong hybrid trc promoter in order to express these genes in the wild-type C. acidovorans. Increased copy-number of genes resulted in significant increase in the activities of corresponding enzymes, which could further be increased by inducing with isopropyl-beta-D-thiogalactopyranoside (IPTG), indicating that the expression is under the transcriptional control of the trc promoter. P(4HB) biosynthesis in the recombinant C. acidovorans increased 2-fold to constitute more than 60 wt% of the dry cell weight. No significant decrease in the number-average molecular weights of P(4HB) in the recombinant strain was observed when compared with that of the wild-type. Freeze-fracture electron microscopy of intracellular P(4HB) granules revealed almost similar fracture morphology to the well-known mushroom-type deformation shown by polyhydroxyalkanoates with medium-chain-length monomers.

Acetyl-CoA C-Acyltransferase↗