No description available.

No description available.

No description available.

No description available.

No description available.

The viable but non-culturable (VBNC) state is outstanding among bacterial stress responses as being completely uncharacterised at the molecular level. The aim of this investigation was to gain an insight into the molecular basis of the condition by identifying genes whose expression was up-regulated in response to VBNC-inducing stimuli. First, a model experimental system was established where bacteria were induced to enter the state in a routine and predictable manner. <I>Escherichia coli </I>HB101 exhibited a partial viable but non-culturable phenotype when inoculated into microcosms of artificial seawater at 37°C, <I>Pseudomonas fluorescens </I>10586 became viable but non-culturable in microcosms of drinking water incubated at 37°C, and <I>Vibrio vulnificus </I>MO6-24/T entered a viable, non-culturable state in artificial seawater at 5°C. A transposon mutagenesis strategy utilising a promoter-less bioluminescent reporter cassette, <I>lux</I>AB, was employed in the search for VBNC-associated genes. The mini-Tn<I>5 lux</I>AB transposon was induced to transform into arbitrary positions of the <I>P. fluorescens </I>10586 chromosome, thus creating a library of <I>P. fluorescens lux</I>AB mutants. This library (consisting of over 1200 transformants) was screened for those which were dark under normal circumstances, but luminesced in response to VBNC stimuli, indicating that the transposon had integrated downstream of a gene up-regulated during the VBNC response. Unfortunately, no mutant examined exhibited such a bioluminescence profile. Differential display of RNA technology was employed subsequently and resulted in the cloning and sequencing of several <I>V. vulnificus </I>transcripts thought to be associated with the VBNC state. Although absolute verification of the involvement of these transcripts was not achieved, hints as to what mechanisms lay at the basis of the VBNC state were gained. Some findings indicated that VBNC cells experience considerable levels of oxidative stress, and it was proposed that this physiological state may lie at the crux of the VBNC phenotype.

<I>Escherichia coli</I> mutants impaired in growth and survival at low external pH in minimal medium were selected and attempts made to identify the disrupted genes. This study suggested that <I>clpX</I>, encoding a heat-shock induced protease and molecular chaperone, was functional in survival of <I>E. coli </I>at pH 3.3. Promoter probe plasmid libraries of <I>Salmonella typhimurium </I>LT2 DNA were created in <I>E. coli </I>and screened for acid-inducible transcriptional elements, and transcriptionally active fragments of degradative amino-acid decarboxylase genes recovered. Chromosomal gene fusions to the reporter gene <I>lacZ </I>in <I>E. coli</I> generated by Mu DII 1734 insertion were screened in a similar way and suggested that the gene encoding adenylate cyclase (<I>cya</I>) could be induced by mild cytoplasmic acidification. The sequence of a gene known to be inducible by cytoplasmic acidification, <I>inaA, </I>became available during the course of this study. The 5' region of this gene was used to generate a set of plasmids carrying fragments of the acid-inducible promoter transcriptionally fused to a luciferase based reporter system. Elements of the sequence required for induction by cytoplasmic acidification were identified. One of these reporter constructs was used to screen an <I>E. coli </I>Tn<I>10</I> chromosomal insertional mutant library for genes involved in the regulation of <I>inaA. </I>One such mutant had a multiple antibiotic resistant (<I>mar</I>) phenotype. The disrupted loci in 2 other mutants were identified by inverse PCR, sequence analysis and database searches. Both were known only as open reading frames (ORFs) discovered during the sequencing of the entire <I>E. coli</I> genome, and were tentatively identified as <I>yddB </I>(closely linked to <I>gadB </I>and <I>gadC</I>; required for glutamate dependent acid resistance) and <I>f300</I> (closely linked to <I>pldA; </I>required for detergent resistance). The promoter of <I>f300</I> was shown to be sensitive to cytoplasmic acidification. The <I>inaA</I> promoter was also demonstrated to be induced at the onset of stationary phase, and to be independent of the stationary phase and weak-acid inducible σ factor RpoS and also of cAMP levels.

Graduation date: 1969

Typescript. / Thesis (Ph. D.)--University of Hawaii at Manoa, 1972. / Bibliography: leaves 91-96. / ix, 96 l illus

Integral membrane proteins perform a wide range of biological processes, including respiration, signal transduction and molecular transport. Structural information is necessary for a full understanding of the mechanisms by which integral membrane proteins work. Ferrous iron transporter protein B (FeoB) is an integral membrane protein of Escherichia coli which is considered to transport ferrous iron in to bacteria. But there are no definite proofs or clear indications of the precise mechanism of ferrous transport. By expressing and crystallizing the G-protein domain (FeoGP) and FeoB, it will be helpful to know about the iron transport system. In order to express FeoB and FeoGP, expression vector pFeoB (FeoB in pGEX-4T-1) and pFeoGP (FeoB in pGEX-4T-1) were made. FeoB and FeoGP proteins were expressed and purified. Using vapour diffusion method crystallization trials of FeoB and FeoGP were done. Crystals of FeoGP are observed and no crystal formation for FeoB. Native crystals of FeoGP diffracted to 2.2 ?? resolution, and mant-GMPPNP crystals to 2.6 ??. Preliminary data processing indicate space group P212121 for native crystals, with cell dimensions 46 x 119 x 146 ??. The data set is 100% complete, Rmerge 0.08, and I/ ?? 3.2.