Progress 10/01/12 to 09/30/17
Outputs
Target Audience:
Nothing Reported
Changes/Problems:The major change was in the approach to determining the fatty acid composition of the lipid tether of GbuC with temperature. The mass spetrometry was performed by personnel at the campus Mass Spectrometry facility. They were not able to obtain reproducible results using whole protein or tryptic digests. We will examine the fatty aids directly using gas chromatography, then repead the mass spectrometry experiments aided by the GC results. We chose mass spectrometry because a preliminary experiment using E. coli instead of L. monocytogenes gave acceptable results. But, the results using E. coli do not tell us anything about L. monocytogenes. Although the PI is retiring, the students will complete their thesis research, and the experimentation will continue. What opportunities for training and professional development has the project provided?Each student has been trained in laboratory safety, BSL2 biosafety and molecular biological techniques including electrophoresis, eletroporation, plasmid design, etc. One of the students was also trained in radiation safety before using carbon-14 in transport experiments. How have the results been disseminated to communities of interest?
Nothing Reported
What do you plan to do during the next reporting period to accomplish the goals?
Nothing Reported
Impacts
What was accomplished under these goals?
Three graduate students worked on the project. One generated mutants in the gene encodingsolute-binding protein GbuC that appended a coding sequence for Green Fluorescent Protein (GFP), and transferred it into L. monocytogenes for incorporation into the L. monocytogenes genome. She also generated a plasmid to fuse a red "GFP" to the transport sytem's ATPAse, GbuA, and is awaiting the success of the allelic recombination of the gene encoding the green protein before incorporating it into the genome of the same strain. The strain will be used for fluorescent microscopic studies of the location and mobility of the components of the transport system. Another student deleted the portion of the gene encoding the NBS region of GbuA, which has been implicated to at as a sensor in activation of the transport system under hyperosmotic upshock. The deletion will be used to assess whether the region of the protein is also involved in activation by cold. The third student has grown L. monocytogenes in the presence of the fatty acid elongation factor inhibitor cerulenin in order tolimit the length of the membrane fatty acids in order to determine whether membrane thickness mediates cold-activated transport. This student also isolated GbuC grown under different conditions to determine whether the fatty acids of the lipid tether of Gbu change with temperature. Mass spectrometry experiments were inconclusive, and we are exploting other approaches.
Publications
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Progress 10/01/15 to 09/30/16
Outputs
Target Audience:
Nothing Reported
Changes/Problems:The membrane thickness and fluorescent protein studies were added in the second half of last year. What opportunities for training and professional development has the project provided?Two graduate students and a visiting scholar were trained in cloning and expression of genes (Primer design, polymerase chain reaction,use of restriction endonucleases, ligation, transformation, gene induction and gene product purification), in general microbiological techniques, and use of radioactivity in transport assays. Sample preparation and interpretation of mass spectrometry data were also learned. How have the results been disseminated to communities of interest?
Nothing Reported
What do you plan to do during the next reporting period to accomplish the goals?LC/MS give qualitative results on the identity of the fatty acids that comprise the membrane tether of GbuC; we will use N-terminal degradation followed by mass spectrometry to determine their identities. The cross complementation of glycine betaine transporters in L. monocytogenes and L. lactis will be completed. The fluorescent versions of GbuC and GbuB are currently expressed using plasmids; at least one of the genes must be inserted into the genome to obtain expression of both proteins in the same cell. The CBS deletion mutant described above will be tested for cold activation. Experiments involving altering the thickness of the membrane will also be attempted. Reconstitution of the Gbu transport system, which was planned for last year, will be attempted, this year.
Impacts
What was accomplished under these goals?
A glycine betaine transport-deficient mutant of (lacking the opuA gene) Lactococcus lactis was obtained from (B. Poolman), and the corresponding transporter from Listeria monocytogenes (gbu) has been expressed in it. Conversely, opuA has been expressed in a gbu-deficient mutant of L. monocytogenes in order to determine whether it is the nature of the membrane or the transport system that confers cold activation of glycine betaine transport, which enables the pathogen to grow in the refrigerator. The membrane-tethered solute binding protein has been expressed in L. monocytogenes at 30 and at 7 degrees C, and analyzed by GC/MS to determine whether the fatty acids of the lipid tether change in parallel to the overall membrane fatty acids, which are largely C17:0 iso-branched at 30 degrees, but shift to C15:0 anteiso-branched at 7 degrees. New experiments involving fluorescently labeled versions of the solute-binding protein (GbuC) and the transmembrane pore protein (GbuB) have been initiated to determine localization, diffusion and co-location of the proteins, and the dependence of these factors on temperature. The CBS region of the pore protein, which has been implicated in hyper-osmotic stress activation of transport has been deleted. the mutant will be tested for cold activation.
Publications
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Progress 10/01/14 to 09/30/15
Outputs
Target Audience:Professional scientists and educators interested in microbiological food safety and/or microbiology. Changes/Problems:The use of L. lactis is a new idea. What opportunities for training and professional development has the project provided?Three graduate students were trained in cloning and expression of genes (Primer design, polymerase chain reaction,use of restriction endonucleases, ligation, transformation, gene induction and gene product purification), and in general microbiological techniques. How have the results been disseminated to communities of interest?Preliminary results were presented as part of the talk at Niigata University of Pharmacy and Applied Life Sciences, Niigata, Japan. What do you plan to do during the next reporting period to accomplish the goals?We will attempt to reconstitute the transport system into artificial membranes. We will also express the Gbu operon in a strain of Lactococcus lactis that lacks the opuA gene, and express L. lactis in a strain of L. monocytogenes that lacks Gbu and OpuC
Impacts
What was accomplished under these goals?
The genes encoding proteins GbuA, abd GbuB have been cloned and expressed in Escherichia coli, and the gene for GbuC has been cloned and expressed in Listeria monocytogenes. These will be used in a reconstitution experiment in 2016, in collaboration with Bert Poolman, in Groningen
Publications
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2015
Citation:
Oral Presentation, The Assumption University of Thailand, "Osmotic and chill tolerance in Listeria monocytogenes".
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Progress 10/01/13 to 09/30/14
Outputs
Target Audience:Professional scientists and educators interested in microbiological food safety and/or microbiology. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?Two graduate students were trained in cloning and expression of genes (Primer design, polymerase chain reaction,use of restriction endonucleases, ligation, transformation, gene induction and gene product purification), and in general microbiological techniques. How have the results been disseminated to communities of interest?Preliminary results were presented as part of the talk at The Assumption University of Thailand. What do you plan to do during the next reporting period to accomplish the goals?The study of Gbu will be continued and expanded to cover GbuA and GbuB. We will attempt to reconstitute the transport system into artificial membranes.
Impacts
What was accomplished under these goals?
The overall goal of this portion of the project is to gain an understanding of the function the Gbu transporter in the resistance of the foodborne pathogen Listeria monocytogenes to hyperosmotic and chill stress. The solute binding protein of this ATP binding cassette transporter bears a diacyl glycerol group at its N terminus, which serves as a tether to the membrane. The diacylglcerol is attached to the sulfur of the cysteine residue that becomes the N terminus after proteolytic processing. The main goals of this portion of the project were two-fold. First, the graduate student repeated her work, but took pains to endure that the GbuC protein contained the hexahistidine tag necessary for purification. 1 clone the gene encoding GbuC from L. monocytogenes in Escherichia coli, 2 transfer the gene to L. monocytogenes, 3 express it at low temperature and at normal temperature, 4 isolate the GbuC protein 5 determine the identity of the fatty acids of the lipid tether Items 1-3 have been completed The second portion of the project also focuses on GbuC. The goals are 1 construct a strain of L. monocytogenes with a deletion of the GbuC gene 2 construct a strain of L. monocytogenes in which the GbuC gene has its single cysteine replaced by an alanine, so that lipidation cannot occur 3 compare growth rates of the two mutants and parent strain under chill stress, hyperosmotic stress and in the absence of stress 3 compare kinetic parameters (Km and Vmax) of the two mutants and parent strain under chill stress, hyperosmotic stress and in the absence of stress items 1 and 2 were accomplished.
Publications
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2014
Citation:
Oral Presentation, The Assumption University of Thailand, "Osmotic and chill tolerance in Listeria monocytogenes".
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Progress 01/01/13 to 09/30/13
Outputs
Target Audience:Professional scientists and educators interested in microbiological food safety and/or microbiology. Changes/Problems:It was found that the GbuC expressed in L. monocytogenes was present in gels, but did not contain the hexahistidine tag that was to be used for purification, so the student began again. What opportunities for training and professional development has the project provided?One graduate student was trained in cloning and expression of genes (Primer design, polymerase chain reaction,use of restriction endonucleases, ligation, transformation, gene induction and gene product purification), and in general microbiological techniques How have the results been disseminated to communities of interest?Preliminary results were presented as part of the talk at Jianang University. What do you plan to do during the next reporting period to accomplish the goals?The study of GbuC will be continued and expanded to cover mechanistic and functional aspects
Impacts
What was accomplished under these goals?
The overall goal of this portion of the project is to gain an understanding of the function the Gbu transporter in the resistance of the foodborne pathogen Listeria monocytogenes to hyperosmotic and chill stress. The solute binding protein of this ATP binding cassette transporter bears a diacyl glycerol group at its N terminus, which serves as a tether to the membrane. The main goals of this portion of the project were to λ clone the gene encoding GbuC from L. monocytogenes in Escherichia coli, λ transfer the gene to L. monocytogenes, λ express it at low temperature and at normal temperature, λ isolate the GbuC protein λ determine the identity of the fatty acids of the lipid tether
Publications
- Type:
Conference Papers and Presentations
Status:
Accepted
Year Published:
2013
Citation:
Oral Presentation, NMR Research at UC Davis, Jiangnan University, Wuxi, Jiangsu, China
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Progress 01/01/12 to 12/31/12
Outputs
OUTPUTS: The gene gbuC encodes a solute binding protein of the Gbu transport system of the food-borne pathogen Listeria monocytogenes (LM). This transport system is critical to the survival of LM under chill or osmotic stress. We are investigating the compositions and function of the lipid tether that fastens GbuC to the membrane. The gene contains a signaling sequence for the secB pathway, which targets the protein to the exterior of the cell, and causes the attachment of a diacylglycerol to the sulfur of the N-terminal cysteine residue after proteolytic processing of the signal peptide. An LM strain harboring a plasmid encoding a hexahistidine-tagged GbuY, and strains with either a deletion or gbuY or a C1->S1 mutant of gbuY, which lacks the cysteine have been revived from storage after a brief period during which the project was not staffed. The hexahistidine-tagged protein has been expressed, and we are now expressing the gene under conditions of high salt and in the cold (7 degrees C). The proteins are to be cleaved using trypsin, and the hydrolysate submitted to LC/MS to determine the molecular weights of the two fatty acids to determine if they are fixed, or if they chance along with the overall fatty acid composition of the membrane, which shofts from longer-chained, iso-branched fatty acids at room temperature, to C15:0 anteiso-branched fatty acids. A new graduate student has been added to the project, and a visiting scholar is scheduled to arrive in the fall to work on expression of gbuA and gbuB in E. coli, which will be used in separate studies of the structure and function of the Gbu system. PARTICIPANTS: Ms. Xinyi Song, a student from Jiangnan University in China, has joined the project to work on GbuC. A visiting professor from Jiangnan University is scheduled to join us in the Fall for a sabbatical leave, during which he will express gbuA and gbuB in E. coli TARGET AUDIENCES: Not relevant to this project. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
The project was stalled when graduate students finished their degrees and left. We are now getting back up to speed. The principal results of this year's work so far is that the strains developed for the study of GbuC are viable and contain the correct plasmid
Publications
- No publications reported this period
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Progress 01/01/11 to 12/31/11
Outputs
OUTPUTS: The project is currently un-staffed. Activity has been restricted to culture maintenance until personnel can be recruited. PARTICIPANTS: Nothing significant to report during this reporting period. TARGET AUDIENCES: Nothing significant to report during this reporting period. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
No outcomes this year.
Publications
- No publications reported this period
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Progress 01/01/10 to 12/31/10
Outputs
OUTPUTS: The focus of the current stage of the project is to determine how the glycine betaine transport system Gbu is activated by chill. Our hypothesis is that transport is activated at low temperature because phospholipids containing longer-chain fatty acids crystallize and leave the protein in a membrane that is enriched in lower-melting lipids, which are two carbon atoms shorter. This narrowing of the membrane causes a further tilt of the transmembrane helices of the pore protein GbuB, which activates transport. Our approach is to clone and express the three proteins comprising the system, and to reconstitute them into artificial phospholipids bilayers of defined thickness. All genes have been cloned for expression in E. coli, and the solute-binding protein-encoding gene can be expressed in L. monocytogenes (because it is processed differently in E. coli). And all have been expressed and purified. The project has stalled temporarily due to manpower shortage. PARTICIPANTS: Nothing significant to report during this reporting period. TARGET AUDIENCES: Nothing significant to report during this reporting period. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
There were no new findings during this period
Publications
- No publications reported this period
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Progress 01/01/09 to 12/31/09
Outputs
OUTPUTS: The mechanism of chill and osmotic tolerance of the food-borne pathogen Listeria monocytogenes is being investigated by examining the structure and function of a transport system that imports protective molecules and my analysis of the composition of the cell membrane. The genes encoding the most important stress-related transporter, Gbu, have been cloned and are being used in various substudies: the investigation of the function of the lipid tether that attaches the binding protein GbuC to the membrane, the mechanism of coupling between ATP hydrolysis and transport, the overall organization of the six polypeptides in the L. monocytogenes membrane, and the nature of the alterations in the membrane of mutants that are unable to synthesize branched-chain fatty acids that form a substantial but variable fraction of the membrane in the wild type. Both the lipid experiments and the experiments involving GbuC are awaiting GC/MS analysis. Therefore, no outputs were completed. PARTICIPANTS: Patchanee Yasurin was a graduate student in the Food Biotechnology program at the Assumption University of Thailand (Bangkok). She pursued her PhD research under my direction at UC Davis under the auspices of an Agreement of Cooperation. She is now teaching at Assumption University. TARGET AUDIENCES: Nothing significant to report during this reporting period. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
Relatively standard methods have been used for this project. These include cloning and sequencing of genes, expression of L. monocytogenes genes in Escherichia coli and in L. monocytogenes, purification of proteins by affinity chromatography, gel electrophoresis of DNA and proteins, lipid extraction and fatty acid methyl ester analysis by gas chromatography. We are awaiting critical measurements before evaluating outcomes and impacts.
Publications
- Purification and characterization of the osmo- and cryoprotective ABC transport system, Gbu, in Listeria monocytogenes. 2009 Min Yang PhD Dissertation, Food Science, University of California, Davis.
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Progress 01/01/08 to 12/31/08
Outputs
OUTPUTS: L. monocytogenes is a serious food-borne pathogen that is notable in its resistance to environmental stresses, including chill and high osmolarity. It is the second largest cause of death from food-borne illness in the US. A key aspect of its ability to survive and grow at refrigeration temperatures is the unusual composition of its membrane, which contains highly saturated fatty acids, many of which are ranched. C15 and C17, both iso- and anteiso- branches are common. The membrane also contains transport proteins Gbu and OpuC that transport glycine betaine and carnitine, respectively, which contribute to both osmotic and chill tolerance and a third transporter, BetL, that transports glycine betaine in response to high salt concentration in the medium. The regulaton of the synthesis of the three transporters, and the mechanism of activation of Gbu and OpuC by chill are all of interest in the effort to reduce food-borne illness due to L. monocytogenes. We have therefore created operon fusions in which the lacZ gene is inserted in the genome preceding a copy of the gene or first gene in the operon that encodes the transporters for studies on the regulation of the synthesis of each transporter at the genetic level. Gbu, the most important of the three transporters, has been cloned and expressed in a project that has recently expired. Additional studies of the L. monocytogenes membrane were also begun. In these studies, the membrane composition was altered by growth at low temperatre, which increases the proportion of C15 fatty acids and anteiso branches, In addition, cold-sesitive mutants exist that are deficient in branched-chain fatty acids. The growth and membrane composition of the membranes of these mutants was studied in the presence and absence of likely alternative primers for unsaturated, atypically-branched or multiply-branched fatty acid synthesis were determined. Glycine betaine transport will be determined in these cultures. The membrane lipids of these mutants have been isolated for future reconstitution of the cloned GbuA,B and C proteins to determine how transport activity can be affected by differing membrane composition. The reconstitution experiments are a follow-up to our expired project. PARTICIPANTS: Gary M. Smith, PI, Professor, UC Davis. Originated all experiments. Patchanee Yasurin, graduate student, Assumption University of Thailand, visiting scholar at UC Davis. Constructed reporter-gene operon fusions, conducted initial quantitative growth experiments and fatty acid analysis of branched chain deficient mutants. Mun Hua Tan, Undergraduate studet, UC Davis, conducted preliminary growth experiments on branched chain deficient mutants. Yinghua Xiao, Graduate student, Waginingen University, visiting scholar, UC Davis, conducted preliminary qualitative screening of potential fatty acid primers in branched chain deficient mutants. Raymond C. Valentine, Prof. Emer., UC Davis, consulted on membrane fluidity and fatty acid primers in L. monocytogenes. TARGET AUDIENCES: Not relevant to this project. PROJECT MODIFICATIONS: Not relevant to this project.
Impacts
Current work has set us up to conduct expression, survival and transport studies. The impact has yet occurred.
Publications
- No publications reported this period
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Progress 01/01/07 to 12/31/07
Outputs
OUTPUTS: When stressed by high salt concentration or refrigeration temperature L. monocytogenes (LM) cells accumulate the protective molecules glycine betaine and carnitine from the environment by the action of three transport systems, Gbu, OpuC and BetL. Regulation of synthesis is being studied using a promoterless lacZ gene inserted behind a copy of the promoter region of the genes encoding the three stress-related transporters. The new emphasis is to determine whether presence of the substrates glycine betaine, carnitine or other factors alter the expression, and if so, by what mechanism. We previously characterized the membrane lipids of LM and found them to contain highly saturated, often branched-chain fatty acids, largely C17:0anteiso at higher temperatures, shifting to C15:0anteiso at lower temperature. Wilkinson showed mutants unable to make branched chain fatty acids are cold sensitive. We have provided alternate fatty acid primers to Wilkinson's mutants, and found that
linoleic, oleic, vaccenic, isolaleric and t-butylactic acids reestablished chill tolerance to the level of the wild type. The properties and compositions of the membranes synthesized with these primers and under various stress conditions are being determined.
PARTICIPANTS: Pachanee Yasurin, Graduate Student, Biotechnology Program, The Assumption University of Thailand. Mun Hua Tan, Undergraduate Student, UC Davis. Yinghua Xiao, Graduate Student, Wagenengin University, The Netherlands
TARGET AUDIENCES: This work will be presented to microbiology and microbial food safety professionals via publication in professional journals and in food science literature
PROJECT MODIFICATIONS: All changes involved changes in methodology to enhance the probability of success.
Impacts
The results are too new to have produced an impact.
Publications
- Yang, M, Yasurin, P. and Smith, G.M. (2007) None
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Progress 01/01/06 to 12/31/06
Outputs
When stressed by high salt concentration or refrigeration temperature L. monocytogenes (LM) cells accumulate the protective molecules glycine betaine and carnitine from the environment by the action of three transport systems, Gbu, OpuC and BetL. Regulation of synthesis is being studied using a promoterless lacZ gene inserted behind a copy of the promoter region of the genes encoding the three stress-related transporters. Our fusion for the opuC operon proved to be faulty, and we generated a new mutant. All three systems are expressed to some extent during balanced growth without added salt stress. Expression is enhanced by the addition of NaCl. Enhancement of expression by chill is more difficult to determine because all processes are slower. The new emphasis is to determine whether presence of the substrates glycine betaine or carnitine alter the expression, and if so, by what mechanism. We previously characterized the membrane lipids of LM and found them to contain
highly saturated, often branched-chain fatty acids, largely C17:0anteiso at higher temperatures, shifting to C15:0anteiso at lower temperature. Wilkinson showed mutants unable to make branched chain fatty acids are cold sensitive. We have provided alternate fatty acid primers to Wilkinson's mutants, and found that some of them conferred cold tolerance. We are now analyzing the lipid composition in these cells.
Impacts
The ultimate impact is to reduce the viability of Listeria monocytogenes, particularly persistent strains, by understanding the mechanism of resistance to environmental stress and refrigeration. Reducing the viability will decrease the loss of life and economin burden of product recalls due to Listeria monocytogenes.
Publications
- No publications reported this period
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Progress 01/01/05 to 12/31/05
Outputs
When stressed by high salt concentration or low (e.g., refrigeration) temperature L. monocytogenes cells accumulate the protective molecules glycine betaine and carnitine from the environment by the action of three transport systems, Gbu, OpuC and BetL. The activities of the transport systems are regulated by the presence of the stress. Previous work in which genes encoding the transport proteins were deleted showed the relative importance of each transport system and the conditions under which it functions. Besides regulation of transport activity at the biochemical level, it is likely that L. monocytogenes regulates the amount of each transport system by controlling synthesis of the proteins at the genetic level. Regulation of synthesis is being studied using a promoterless lacZ gene inserted behind a copy of the promoter region of the gbu gene, and similar constructs involving two other stress-related transporters, BetL and OpuC. We grow the cells in the asence of
stress and the absence of glycine betaine and carnitine, and test the expression of the reporter gene when the cells are subjected to salt stress, salt stress not involving sodium ion, sugar-mediated osmotic stress and chill stress. We are also testing whether the presence or absence of substrates glycine betaine and carnitine affect expression. Assays using the chromogenic substrate OMPG proved not to be sufficiently sensitive, and we have begun using the fluorogenic substrate MUG. Preliminary results indicate that the transporters are at least partially constitutive, and are present even in rich media unsupplemented with salt.
Impacts
The ultimate impact is to reduce the viability of Listeria monocytogenes, particularly persistent strains, by understanding the mechanism of resistance to environmental stress and refrigeration. Reducing the viability will decrease the loss of life and economin burden of product recalls due to Listeria monocytogenes.
Publications
- No publications reported this period
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Progress 01/01/04 to 12/31/04
Outputs
Our objectives were to measure expression of the three compatible solute transporters (Gbu, BetL and OpuC) of Listeria monocytogenes using reporter gene fusions, express green fluorescent protein (GFP)-labeled proteins of the Gbu transport system, and purify histidine-tagged GbuA, GbuB and GbuC. The expression of Gbu and BetL was measured in response to salt stress, osmotic stress (sucrose) and chill stress in the presence and absence of glycine betaine and carnitine. The OpuC label proved to be faulty and we are currently preparing a new strain. E. coli strains harboring plasmids containing genes encoding hexahistidine-tagged GbuA, GbuB and GbuC under the control of a Lac promoter have been prepared and the proteins are being purified using zinc affinity chromatography. The gene encoding GFP has been cloned into a plasmid suitable for our purposes.
Impacts
The ultimate impact is to reduce the viability of Listeria monocytogenes, particularly persistent strains, by understanding the mechanism of resistance to environmental stress and refrigeration.
Publications
- No publications reported this period
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Progress 01/01/03 to 12/31/03
Outputs
LISTERIA MONOCYTOGENES is a foodborne pathogen that survives under hyperosmotic stress and grows at refrigeration temperatures. Solute transport systems aid in the stress-hardiness by importing the protective molecules glycine betaine and carnitine, which are found in the food. Deletion experiments showed that there are three separate transport systems that are responsible for stress-activated transport of these solutes; they are encoded by the gbu and opuC operons and the betL gene. Gbu and BetL are primarily glycine betaine transporters and OpuC is a carnitine transporter, although Gbu and OpuC show some transport of the other solute. These two transporters are activated by chill or by hyperosmotic stress, whereas BetL is activated by hyperosmotic stress. Operon fusions of a reporter gene show that expression of gbu and betL is enhanced under stress; the fusion mutant involving opuC is defective and it is being re-designed.
Impacts
Knowledge of the mechanism of osmotic tolerance and of growth In the refrigerator should lead to food formulations that do not support growth of L. MONOCYTOGENES under osmotic or chill stress, and to the design of better cleaning regimens and handling methods to reduce the possibility of contamination of food by equipment or from the processing environment.
Publications
- Angelidis, A.S., Smith, L.T. and Smith, G.M. 2002. Elevated carnitine accumulation by LISTERIA MONOCYTOGENES impaired in glycine betaine transport is insufficient to restore wild-type cryotolerance in milk whey. Int. J. Food Micro. 75(1-2):1-9.
- Angelidis, A.S., Smith, L.T., Hoffman, L.M. and Smith, G.M. 2002. Identification of OpuC as a chill-activated and osmotically activated carnitine transporter in LISTERIA MONOCYTOGENES. Appl. Environ. Microbiol. 68(6):2644-2650.
- Angelidis, A.S. and Smith, G.M. 2003. Three transporters mediate uptake of glycine betaine and carnitine by LISTERIA MONOCYTOGENES in response to hyperosmotic stress. Appl. Environ. Microbiol. 69(2):1013-1022.
- Angelidis, A.S. and Smith, G.M. 2003. The role of the glycine betaine and carnitine transporters in adaptation to chill stress by LISTERIA MONOCYTOGENES in defined medium. Appl. Environ. Microbiol. 69(12):7492-7498.
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