Biomedical subjects

Jong-In Han

Publications and source records attributed to Jong-In Han.

4 recordsLinked to original sources

PubMed2005

Utilization of homoserine lactone as a sole source of carbon and energy by soil Arthrobacter and Burkholderia species.

Homoserine lactone (HSL) is a ubiquitous product of metabolism. It is generated by all known biota during the editing of certain mischarged aminoacyl-tRNA reactions, and is also released as a product of quorum signal degradation by bacterial species expressing acyl-HSL acylases. Little is known about its environmental fate over long or short periods of time. The mammalian enzyme paraoxonase, which has no known homologs in bacteria, has been reported to degrade HSL via a lactonase mechanism. Certain strains of Variovorax and Arthrobacter utilize HSL as a sole source of nitrogen, but not as a sole source of carbon or energy. In this study, the enrichment and isolation of four strains of soil bacteria capable of utilizing HSL as a carbon and energy source are described. Phylogenetic analysis of these isolates indicates that three are distinct members of the genus Arthrobacter, whereas the fourth clusters within the non-clinical Burkholderia. The optimal pH for growth of the isolates ranged from 6.0 to 6.5, at which their HSL-dependent doubling times ranged from 1.4 to 4 h. The biodegradation of HSL by these 4 isolates far outpaced its chemical decay. HSL degradation by soil bacteria has implications for the consortial mineralization of acyl-homoserine lactones by bacteria associated with quorum sensing populations.

4-Butyrolactone↗

PubMed2005

Quantitative community analysis: capillary electrophoresis techniques.

This chapter presents methodologies for RNA extraction from soils coupled with competitive reverse transcription-polymerase chain reaction and capillary electrophoresis techniques. Combined, these approaches provide new capabilities to quantify gene expression in different environments and can aid our understanding of not only community composition, but also community activity. Such information will prove important for enhancing our knowledge of how microbial communities respond to changing geochemical parameters (e.g., temperature, pH, redox conditions, substrate levels) in situ.

Electrophoresis, Capillary↗

PubMed2004

Quantification of gene expression in methanotrophs by competitive reverse transcription-polymerase chain reaction.

To improve the monitoring of methanotrophic activity, a competitive reverse transcription-polymerase chain reaction (RT-PCR) methodology was developed. Homologous internal RNA standards were created for mmoX and pmoA, genes encoding polypeptides of sMMO and pMMO, respectively. Using specific primer sets, expression of sMMO and pMMO could be quantified by means of competitive RT-PCR and capillary electrophoresis with uncoated bare-fused silica columns and UV detection. Using this technique, it was discovered that the amount of mRNA transcript for both mmoX and pmoA correlated well with whole-cell sMMO and pMMO activity respectively. A method for soil RNA extraction was also developed to utilize this RNA quantification technique for the monitoring of methanotrophic activity in situ. In a model soil slurry system with a background concentration of 2.9 micro M copper, it was found that only pmoA was transcribed by cells capable of expressing both forms of MMO. As pMMO and sMMO have very different substrate ranges and kinetics, this methodology may prove useful for optimizing in situ bioremediation by methanotrophs. Provided sufficient sequence information is available to create specific primer sets, these techniques can be applied for monitoring and measuring the activity of other microbial communities in situ.

Bacterial Proteins↗

PubMed2003

Utilization of acyl-homoserine lactone quorum signals for growth by a soil pseudomonad and Pseudomonas aeruginosa PAO1.

Acyl-homoserine lactones (AHLs) are employed by several Proteobacteria as quorum-sensing signals. Past studies have established that these compounds are subject to biochemical decay and can be used as growth nutrients. Here we describe the isolation of a soil bacterium, Pseudomonas strain PAI-A, that degrades 3-oxododecanoyl-homoserine lactone (3OC12HSL) and other long-acyl, but not short-acyl, AHLs as sole energy sources for growth. The small-subunit rRNA gene from strain PAI-A was 98.4% identical to that of Pseudomonas aeruginosa, but the soil isolate did not produce obvious pigments or AHLs or grow under denitrifying conditions or at 42 degrees C. The quorum-sensing bacterium P. aeruginosa, which produces both 3OC12HSL and C4HSL, was examined for the ability to utilize AHLs for growth. It did so with a specificity similar to that of strain PAI-A, i.e., degrading long-acyl but not short-acyl AHLs. In contrast to the growth observed with strain PAI-A, P. aeruginosa strain PAO1 growth on AHLs commenced only after extremely long lag phases. Liquid-chromatography-atmospheric pressure chemical ionization-mass spectrometry analyses indicate that strain PAO1 degrades long-acyl AHLs via an AHL acylase and a homoserine-generating HSL lactonase. A P. aeruginosa gene, pvdQ (PA2385), has previously been identified as being a homologue of the AHL acylase described as occurring in a Ralstonia species. Escherichia coli expressing pvdQ catalyzed the rapid inactivation of long-acyl AHLs and the release of HSL. P. aeruginosa engineered to constitutively express pvdQ did not accumulate its 3OC12HSL quorum signal when grown in rich media. However, pvdQ knockout mutants of P. aeruginosa were still able to grow by utilizing 3OC12HSL. To our knowledge, this is the first report of the degradation of AHLs by pseudomonads or other gamma-Proteobacteria, of AHL acylase activity in a quorum-sensing bacterium, of HSL lactonase activity in any bacterium, and of AHL degradation with specificity only towards AHLs with long side chains.

4-Butyrolactone↗