No description available.

The adhesion of seven meat spoilage bacteria to model meat surfaces (thin fat and tendon slices) was studied in a specially designed flow chamber. In general, adhesion was not influenced by the physiological age of the cells and was not correlated with the cell surface characteristics (electrical charge, hydrophobicity) of the organisms. Also, adhesion data did not corroborate the predictions based on changes in the free energy of adhesion, calculated from contact angles and surface tension measurements. A more detailed study of the adhesion of Pseudomonas fluorescens to tendon was subsequently undertaken. Neither physiological activity nor the presence of flagella was found to be essential for adhesion. Selective chemical alterations of the cell surface pointed to no direct implication of carboxyl or amino groups in an adhesive bond with tendon. These groups may participate in adhesion, however, through electrostatic interactions as suggested from the variations of adhesion with ionic strength.

No description available.

Thesis (Ph. D)--Ohio State University, 2003. / Title from first page of PDF file. Document formatted into pages; contains xvi, 196 p.: ill. Includes abstract and vita. Advisor: Herbert W. Ockerman, Dept. of Animal Science. Includes bibliographical references (p. 185-196).

Thesis (Ph. D.)--University of Alberta, 2009. / Title from pdf file main screen (viewed on Sept. 24, 2009). "A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Chemical Engineering, Department of Chemical and Materials Engineering, University of Alberta." Includes bibliographical references.

Thesis (M.Sc.)--Memorial University of Newfoundland, 1997. / Restricted until May 1998. Bibliography: leaves 90-102.

Submitted by Nathália Faria da Silva (nathaliafsilva.ufv@gmail.com) on 2017-06-19T12:02:55Z No. of bitstreams: 1 texto completo.pdf: 1276596 bytes, checksum: e320e36eac8ecfc4d887e0c9f618329e (MD5) / Made available in DSpace on 2017-06-19T12:02:55Z (GMT). No. of bitstreams: 1 texto completo.pdf: 1276596 bytes, checksum: e320e36eac8ecfc4d887e0c9f618329e (MD5) Previous issue date: 2005-04-29 / Conselho Nacional de Desenvolvimento Científico e Tecnológico / Por meio de um mecanismo denominado quorum sensing, diversas bactérias podem comunicar-se umas com as outras e coordenar a expressão gênica de acordo com a densidade populacional de forma semelhante aos organismos multicelulares. Este trabalho teve como objetivo investigar a produção de moléculas sinalizadoras de quorum, conhecidas como homoserinas lactonas aciladas (AHLs), por bactérias psicrotróficas proteolíticas isoladas de leite cru refrigerado. Verificou-se também se a atividade proteolítica de Pseudomonas fluorescens 07A é dependente da densidade populacional. Foram avaliados 53 isolados psicrotróficos proteolíticos e sete estirpes ATCC quanto à produção de AHL em meio sólido utilizando as bactérias Agrobacterium tumefaciens A136, Chromobacterium violaceum CV026 e Escherichia coli pSB403 como sistemas monitores ou sensores da presença de AHL. A produção de moléculas sinalizadoras foi freqüente entre os isolados psicrotróficos proteolíticos, constatando-se que, aproximadamente, 89 % das estirpes avaliadas foram produtoras de AHL. A extração de moléculas autoindutoras foi realizada em dois isolados, Serratia liquefaciens 016 e P. fluorescens 07A e, a presença de AHL nos extratos foi confirmada pelas estirpes monitoras C. violaceum CV026 e A. tumefaciens KYC55, respectivamente. A produção de AHL pelo isolado P. fluorescens 07A foi determinada em meio de cultivo à base de triptona suplementado com 0,25 % de cálcio (TYEP + CaCl 2 0,25 %) e em meio de constituição mínima (MMS), utilizando a estirpe monitora A. tumefaciens KYC55. Em meio TYEP + CaCl 2 0,25 % a produção de AHL(s) alcançou o máximo ao final da fase logarítmica, quando a população de P. fluorescens 07A foi da ordem de 10 9 UFC mL -1 . Esta mesma população resultou em uma concentração de AHL(s) cerca de três vezes menor no MMS. Os resultados indicaram que a produção de AHL pode estar sob controle de autoindução. O crescimento e a atividade proteolítica do isolado 07A foram avaliados em seis meios de cultivo. Não foi observada diferença no crescimento do isolado nos diferentes meios, exceto no MMS, onde a estirpe cresceu de forma mais lenta. Entretanto, a produção de proteases foi maior em meio TYEP + CaCl 2 0,25 % e em leite desnatado reconstituído (LDR 12 %). A detecção da atividade proteolítica só foi possível quando a cultura atingiu concentração populacional elevada em todos os meios avaliados, excetuando-se no meio MMS, quando a atividade proteolítica foi detectada em uma densidade populacional 10 vezes menor. Nos meios a base de triptona o pH aumentou para valores próximos a 8,5. Meios contendo íons Ca +2 apresentaram grande fluorescência ao final do período de incubação, indicando maior produção do sideróforo pioverdina. A adição de duas AHLs sintéticas não afetou o crescimento e a atividade proteolítica da estirpe P. fluorescens 07A em meio TYEP + CaCl 2 0,25 %. Quando comparada ao controle, a atividade proteolítica específica de P. fluorescens 07A não foi afetada significativamente, ao nível de 5% de probabilidade, pela suplementação do meio TYEP + CaCl 2 0,25 % com extrato de AHL obtido da própria estirpe. O quorum sensing pode não estar regulando a atividade proteolítica em P. fluorescens 07A. / In a process called quorum sensing, a range of bacterial cells communicate and coordinate the expression of multiple phenotypes according to cell density. This work aimed to evaluate the production of signaling molecules known as N-acyl homoserine lactone (AHL) by psychrotrophic proteolytic bacteria isolated from raw milk as well as to verify if the proteolytic activity of Pseudomonas fluorescens 07A is under the control of quorum sensing. Fifty three psychrotrophic isolates and seven ATCC cultures were screened for the production of AHL in agar systems using the monitor strains Agrobacterium tumefaciens A136, Chromobacterium violaceum CV026 and Escherichia coli pSB403. It was verified that almost 89 % of the psychrotrophic isolates tested elicited a positive response in at least one of the monitor strains of AHL. Signaling molecules were extracted from Serratia liquefaciens 016 and P. fluorescens 07A and the presence of AHL was detected with the monitor strains C. violaceum CV026 and A. tumefaciens KYC55, respectively. The production of AHL by the strain 07A was evaluated in a complex medium (TYEP + CaCl 2 0,25 %) and a defined medium (MMS). A. tumefaciens KYC55 was used to quantify AHL in this assay. In TYEP + CaCl 2 0,25 % the AHL concentration reached a maximum value at the end of xvthe stationary phase, when the population of P. fluorescens 07A was 10 9 CFU mL -1 . When MMS medium was used, a similar cell population was achieved, but the AHL concentration was three fold lower. The results indicated that AHL production by P. fluorescens 07A could be regulated by autoinduction. The growth and proteolytic activity of the P. fluorescens 07A were monitored in six different media. It was not observed difference in the specific growth rate of the strain in the media tested, except in MMS, where it grew slower. On the other hand, the protease activity was higher in the complex medium (TYEP + CaCl 2 0,25 %) and reconstituted skimmed milk (LDR 12 %). Proteolytic activity was only detected when the culture reached high population densities (10 8 UFC mL -1 ) in all media evaluated. In MMS, proteolytic activity was detected at lower population densities (10 7 UFC ml -1 ). An increase in pH values was observed during cultivation in media containing tryptone. The emission of fluorescence was intensified in media containing calcium. The addition of two synthetic AHLs did not affect the growth rates and the proteolytic activity of the strain 07A in TYEP + CaCl 2 0,25 %. Furthermore, the addition of AHL extracted from the culture did not increase the specific proteolytic activity in TYEP + CaCl 2 0,25 %. These results indicate that quorum sensing may not have a direct role in the regulation of protease production in P. fluorescens 07A.

Synonymous mutations have traditionally been thought to have no significant effect on fitness. However, a growing body of recent research has shown that this is not always the case. In an experimentally evolved population of Pseudomonas fluorescens grown in minimal glucose media, synonymous mutations arose in a glucose transport gene that resulted in beneficial fitness effects comparable to those of non-synonymous mutations. We found that the increase in fitness was a direct result of increased gene expression; however, the precise mechanism was unclear. Synonymous mutations have been shown to affect gene expression on transcriptional and translational levels through changes in mRNA secondary structure and codon usage. Our study investigates the underlying mechanisms in which these evolved synonymous mutations lead to increased gene expression. In addition to the evolved mutations, we have a library of 42 strains with single synonymous mutations within the glucose transport gene and found a positive correlation between fitness and gene expression. To determine whether these mutations affect transcript levels, translational efficiency or a combination of both, we systematically incorporated transcriptional and translational fusions of a yellow fluorescent protein within the glucose transport operon. We found that the evolved mutations predominantly act on the level of transcription and have strong polar downstream effects. Additionally, through manipulation of the local genetic sequence, we investigated the specific molecular requirements necessary for the increased expression. We found that for one of our evolved synonymous mutants, mRNA secondary structure does not play an essential role, but we speculate that the mutation may strengthen a weak internal promoter sequence to confer its increased expression. Our study provides evidence of the adaptive mechanisms of beneficial synonymous mutations in an experimentally evolved setting.

Cyanide utilization in Pseudomonas fluorescens NCIMB 11764 occurs via oxidative conversion to carbon dioxide and ammonia, the latter satisfying the nitrogen requirement. Substrate attack is initiated by an enzyme referred to as cyanide oxygenase (CNO), previously shown to require components in both high (H) (>30 kDa) and low (L) (<10 kDa) molecular weight cell fractions. In this study, tetrahydrobiopterin (H4biopterin) was identified as a cofactor in fraction L, thus making CNO appear as a pterin- dependent hydroxylase. CNO was purified 150-fold (specific activity 0.9 U/mg) and quantitatively converted cyanide to formate and ammonia as reaction products. When coupled with formate dehydrogenase, the complete enzymatic system for cyanide oxidation to carbon dioxide and ammonia was reconstituted. CNO was found to be an aggregate of known enzymes that included NADH oxidase (Nox), NADH peroxidase (Npx), cyanide dihydratase (CynD) and carbonic anhydrase (CA). A complex multi-step reaction mechanism is proposed in which Nox generates hydrogen peroxide which in turn is utilized by Npx to catalyze the oxygenation of cyanide to formamide accompanied by the consumption of one and two molar equivalents of oxygen and NADH, respectively. The further hydrolysis of formamide to ammonia and formate is thought to be mediated by CynD. The role of H4biopterin and of the enzyme CA in the proposed process remains unclear, but the involvement of each in reactive oxygen and radical chemistry is consistent with the proposed formation of such species in the catalytic process. H4biopterin may additionally serve as a protein stabilizing agent along with a protein co-purifying with CynD identified as elongation factor Tu, a known chaperone. At least two of the CNO components (Nox and CynD) are complex oligomeric proteins whose apparent association with Npx and CA appears to be favored in bacterial cells induced with cyanide allowing their purification in toto as a multiprotein enzyme complex.

No description available.