Posted in Microbiology on 09/08/2010 12:01 pm by Axelsson-Olsson D, Svensson L, Olofsson J, Salomon P, Waldenström J, Ellström P, Olsen B
Increase in acid tolerance of Campylobacter jejuni through coincubation with amoebae.
Appl Environ Microbiol. 2010 Jul;76(13):4194-200
Authors: Axelsson-Olsson D, Svensson L, Olofsson J, Salomon P, Waldenström J, Ellström P, Olsen B
Campylobacter jejuni is a recognized and common gastrointestinal pathogen in most parts of the world. Human infections are often food borne, and the bacterium is frequent among poultry and other food animals. However, much less is known about the epidemiology of C. jejuni in the environment and what mechanisms the bacterium depends on to tolerate low pH. The sensitive nature of C. jejuni stands in contrast to the fact that it is difficult to eradicate from poultry production, and even more contradictory is the fact that the bacterium is able to survive the acidic passage through the human stomach. Here we expand the knowledge on C. jejuni acid tolerance by looking at protozoa as a potential epidemiological pathway of infection. Our results showed that when C. jejuni cells were coincubated with Acanthamoeba polyphaga in acidified phosphate-buffered saline (PBS) or tap water, the bacteria could tolerate pHs far below those in their normal range, even surviving at pH 4 for 20 h and at pH 2 for 5 h. Interestingly, moderately acidic conditions (pH 4 and 5) were shown to trigger C. jejuni motility as well as to increase adhesion/internalization of bacteria into A. polyphaga. Taken together, the results suggest that protozoa may act as protective hosts against harsh conditions and might be a potential risk factor for C. jejuni infections. These findings may be important for our understanding of C. jejuni passage through the gastrointestinal tract and for hygiene practices used in poultry settings.
PMID: 20453130 [PubMed - indexed for MEDLINE]
Posted in Microbiology on 09/08/2010 12:01 pm by Halos L, Bord S, Cotté V, Gasqui P, Abrial D, Barnouin J, Boulouis HJ, Vayssier-Taussat M, Vourc'h G
Ecological factors characterizing the prevalence of bacterial tick-borne pathogens in Ixodes ricinus ticks in pastures and woodlands.
Appl Environ Microbiol. 2010 Jul;76(13):4413-20
Authors: Halos L, Bord S, Cotté V, Gasqui P, Abrial D, Barnouin J, Boulouis HJ, Vayssier-Taussat M, Vourc'h G
Ecological changes are recognized as an important driver behind the emergence of infectious diseases. The prevalence of infection in ticks depends upon ecological factors that are rarely taken into account simultaneously. Our objective was to investigate the influences of forest fragmentation, vegetation, adult tick hosts, and habitat on the infection prevalence of three tick-borne bacteria, Borrelia burgdorferi sensu lato, Anaplasma phagocytophilum, and Rickettsia sp. of the spotted fever group, in questing Ixodes ricinus ticks, taking into account tick characteristics. Samples of questing nymphs and adults were taken from 61 pastures and neighboring woodlands in central France. The ticks were tested by PCR of pools of nymphs and individual adults. The individual infection prevalence was modeled using multivariate regression. The highest infection prevalences were found in adult females collected in woodland sites for B. burgdorferi sensu lato and A. phagocytophilum (16.1% and 10.7%, respectively) and in pasture sites for Rickettsia sp. (8.7%). The infection prevalence in nymphs was lower than 6%. B. burgdorferi sensu lato was more prevalent in woodlands than in pastures. Forest fragmentation favored B. burgdorferi sensu lato and A. phagocytophilum prevalence in woodlands, and in pastures, the B. burgdorferi sensu lato prevalence was favored by shrubby vegetation. Both results are probably because large amounts of edges or shrubs increase the abundance of small vertebrates as reservoir hosts. The Rickettsia sp. prevalence was maximal on pasture with medium forest fragmentation. Female ticks were more infected by B. burgdorferi sensu lato than males and nymphs in woodland sites, which suggests an interaction between the ticks and the bacteria. This study confirms the complexity of the tick-borne pathogen ecology. The findings support the importance of small vertebrates as reservoir hosts and make a case for further studies in Europe on the link between the composition of the reservoir host community and the infection prevalence in ticks.
PMID: 20453131 [PubMed - indexed for MEDLINE]
Posted in Microbiology on 09/08/2010 12:01 pm by Cooksley CM, Davis IJ, Winzer K, Chan WC, Peck MW, Minton NP
Regulation of neurotoxin production and sporulation by a Putative agrBD signaling system in proteolytic Clostridium botulinum.
Appl Environ Microbiol. 2010 Jul;76(13):4448-60
Authors: Cooksley CM, Davis IJ, Winzer K, Chan WC, Peck MW, Minton NP
A significant number of genome sequences of Clostridium botulinum and related species have now been determined. In silico analysis of these data revealed the presence of two distinct agr loci (agr-1 and agr-2) in all group I strains, each encoding putative proteins with similarity to AgrB and AgrD of the well-studied Staphylococcus aureus agr quorum sensing system. In S. aureus, a small diffusible autoinducing peptide is generated from AgrD in a membrane-located processing event that requires AgrB. Here the characterization of both agr loci in the group I strain C. botulinum ATCC 3502 and of their homologues in a close relative, Clostridium sporogenes NCIMB 10696, is reported. In C. sporogenes NCIMB 10696, agr-1 and agr-2 appear to form transcriptional units that consist of agrB, agrD, and flanking genes of unknown function. Several of these flanking genes are conserved in Clostridium perfringens. In agreement with their proposed role in quorum sensing, both loci were maximally expressed during late-exponential-phase growth. Modulation of agrB expression in C. sporogenes was achieved using antisense RNA, whereas in C. botulinum, insertional agrD mutants were generated using ClosTron technology. In comparison to the wild-type strains, these strains exhibited drastically reduced sporulation and, for C. botulinum, also reduced production of neurotoxin, suggesting that both phenotypes are controlled by quorum sensing. Interestingly, while agr-1 appeared to control sporulation, agr-2 appeared to regulate neurotoxin formation.
PMID: 20453132 [PubMed - indexed for MEDLINE]
Posted in Microbiology on 09/08/2010 12:01 pm by Król JE, Rogers LM, Krone SM, Top EM
Dual reporter system for in situ detection of plasmid transfer under aerobic and anaerobic conditions.
Appl Environ Microbiol. 2010 Jul;76(13):4553-6
Authors: Król JE, Rogers LM, Krone SM, Top EM
We designed a new genetic tool to detect plasmid transfer under anaerobic and aerobic conditions. The system is based on the T7 RNA polymerase gene and a T7 promoter-driven oxygen-independent green fluorescent protein, evoglow, alone or in combination with red fluorescent protein DsRed. Constructs are available as plasmids and mini-mariner transposons.
PMID: 20453134 [PubMed - indexed for MEDLINE]
Posted in Microbiology on 09/08/2010 12:01 pm by Abdullah-Al-Mahin , Sugimoto S, Higashi C, Matsumoto S, Sonomoto K
Improvement of multiple-stress tolerance and lactic acid production in Lactococcus lactis NZ9000 under conditions of thermal stress by heterologous expression of Escherichia coli DnaK.
Appl Environ Microbiol. 2010 Jul;76(13):4277-85
Authors: Abdullah-Al-Mahin , Sugimoto S, Higashi C, Matsumoto S, Sonomoto K
The effects of nisin-induced dnaK expression in Lactococcus lactis were examined, and this expression was shown to improve stress tolerance and lactic acid fermentation efficiency. Using a nisin-inducible expression system, DnaK proteins from L. lactis (DnaK(Lla)) and Escherichia coli (DnaK(Eco)) were produced in L. lactis NZ9000. In comparison to a strain harboring the empty vector pNZ8048 (designated NZ-Vector) and one expressing dnaK(Lla) (designated NZ-LDnaK), the dnaK(Eco)-expressing strain, named NZ-EDnaK, exhibited more tolerance to heat stress at 40 degrees C in GM17 liquid medium. The cell viability of NZ-Vector was reduced 4.6-fold after 6 h of heat treatment. However, NZ-EDnaK showed 13.5-fold increased viability under these conditions, with a very low concentration of DnaK(Eco) production. Although the heterologous expression of dnaK(Eco) did not effect DnaK(Lla) production, heat treatment increased the DnaK(Lla) level 3.5- and 3.6-fold in NZ-Vector and NZ-EDnaK, respectively. Moreover, NZ-EDnaK showed tolerance to multiple stresses, including 3% NaCl, 5% ethanol, and 0.5% lactic acid (pH 5.47). In CMG medium, the lactate yield and the maximum lactate productivity of NZ-EDnaK were higher than the corresponding values for NZ-Vector at 30 degrees C. Interestingly, at 40 degrees C, these values of NZ-EDnaK were not significantly different from the corresponding values for the control strain at 30 degrees C. Lactate dehydrogenase (LDH) activity was also found to be stable at 40 degrees C in the presence of DnaK(Eco). These findings suggest that the heterologous expression of dnaK(Eco) enhances the quality control of proteins and enzymes, resulting in improved growth and lactic acid fermentation at high temperature.
PMID: 20453133 [PubMed - indexed for MEDLINE]
Posted in Microbiology on 09/08/2010 12:00 pm by Wei W, Wang FQ, Fan SY, Wei DZ
Inactivation and augmentation of the primary 3-ketosteroid-{delta}1- dehydrogenase in Mycobacterium neoaurum NwIB-01: biotransformation of soybean phytosterols to 4-androstene- 3,17-dione or 1,4-androstadiene-3,17-dione.
Appl Environ Microbiol. 2010 Jul;76(13):4578-82
Authors: Wei W, Wang FQ, Fan SY, Wei DZ
3-Ketosteroid-Delta(1)-dehydrogenase, KsdD(M), was identified by targeted gene disruption and augmentation from Mycobacterium neoaurum NwIB-01, a newly isolated strain. The difficulty of separating 4-androstene-3,17-dione (AD) from 1,4-androstadiene-3,17-dione (ADD) is a key bottleneck to the microbial transformation of phytosterols in industry. This problem was tackled via genetic manipulation of the KsdD-encoding gene. Mutants in which KsdD(M) was inactivated or augmented proved to be good AD(D)-producing strains.
PMID: 20453136 [PubMed - indexed for MEDLINE]
Posted in Microbiology on 09/08/2010 12:00 pm by Kawasaki T, Hirashima R, Maruta T, Sato H, Maeda A, Yamada Y, Takeda M, Hayakawa Y
Cloning and characterization of a gene cluster for hatomarubigin biosynthesis in Streptomyces sp. strain 2238-SVT4.
Appl Environ Microbiol. 2010 Jul;76(13):4201-6
Authors: Kawasaki T, Hirashima R, Maruta T, Sato H, Maeda A, Yamada Y, Takeda M, Hayakawa Y
Streptomyces sp. strain 2238-SVT4 produces hatomarubigins A, B, C, and D, which belong to the angucycline family. Among them, hatomarubigin D has a unique dimeric structure with a methylene linkage. PCR using aromatase and cyclase gene-specific primers identified the hrb gene cluster for angucycline biosynthesis in Streptomyces sp. 2238-SVT4. The cluster consisted of 30 open reading frames, including those for the minimal polyketide synthase, ketoreductase, aromatase, cyclase, O-methyltransferase, oxidoreductase, and oxygenase genes. Expression of a part of the gene cluster containing hrbR1 to hrbX in Streptomyces lividans TK23 resulted in the production of hatomarubigins A, B, and C. Hatomarubigin D was obtained from the conversion of hatomarubigin C by a purified enzyme encoded by hrbY, among the remaining genes.
PMID: 20453135 [PubMed - indexed for MEDLINE]
Posted in Microbiology on 09/08/2010 12:00 pm by Elbahloul Y, Steinbüchel A
Pilot-scale production of fatty acid ethyl esters by an engineered Escherichia coli strain harboring the p(Microdiesel) plasmid.
Appl Environ Microbiol. 2010 Jul;76(13):4560-5
Authors: Elbahloul Y, Steinbüchel A
Fatty acid ethyl esters (FAEEs) were produced in this study by the use of an engineered Escherichia coli p(Microdiesel) strain. Four fed-batch pilot scale cultivations were carried out by first using glycerol as sole carbon source for biomass production before glucose and oleic acid were added as carbon sources. Cultivations yielded a cell density of up to 61 +/- 3.1 g of cell dry mass (CDM) per liter and a maximal FAEE content of 25.4% +/- 1.1% (wt/wt) of CDM.
PMID: 20453138 [PubMed - indexed for MEDLINE]
Posted in Microbiology on 09/08/2010 12:00 pm by Corradini MG, Normand MD, Eisenberg M, Peleg M
Evaluation of a stochastic inactivation model for heat-activated spores of Bacillus spp.
Appl Environ Microbiol. 2010 Jul;76(13):4402-12
Authors: Corradini MG, Normand MD, Eisenberg M, Peleg M
Heat activates the dormant spores of certain Bacillus spp., which is reflected in the "activation shoulder" in their survival curves. At the same time, heat also inactivates the already active and just activated spores, as well as those still dormant. A stochastic model based on progressively changing probabilities of activation and inactivation can describe this phenomenon. The model is presented in a fully probabilistic discrete form for individual and small groups of spores and as a semicontinuous deterministic model for large spore populations. The same underlying algorithm applies to both isothermal and dynamic heat treatments. Its construction does not require the assumption of the activation and inactivation kinetics or knowledge of their biophysical and biochemical mechanisms. A simplified version of the semicontinuous model was used to simulate survival curves with the activation shoulder that are reminiscent of experimental curves reported in the literature. The model is not intended to replace current models to predict dynamic inactivation but only to offer a conceptual alternative to their interpretation. Nevertheless, by linking the survival curve's shape to probabilities of events at the individual spore level, the model explains, and can be used to simulate, the irregular activation and survival patterns of individual and small groups of spores, which might be involved in food poisoning and spoilage.
PMID: 20453137 [PubMed - indexed for MEDLINE]
Posted in Microbiology on 09/08/2010 12:00 pm by Salazar E, DÃaz-MejÃa JJ, Moreno-Hagelsieb G, MartÃnez-Batallar G, Mora Y, Mora J, Encarnación S
Characterization of the NifA-RpoN regulon in Rhizobium etli in free life and in symbiosis with Phaseolus vulgaris.
Appl Environ Microbiol. 2010 Jul;76(13):4510-20
Authors: Salazar E, DÃaz-MejÃa JJ, Moreno-Hagelsieb G, MartÃnez-Batallar G, Mora Y, Mora J, Encarnación S
The NifA-RpoN complex is a master regulator of the nitrogen fixation genes in alphaproteobacteria. Based on the complete Rhizobium etli genome sequence, we constructed an R. etli CFN42 oligonucleotide (70-mer) microarray and utilized this tool, reverse transcription (RT)-PCR analysis (transcriptomics), proteomics, and bioinformatics to decipher the NifA-RpoN regulon under microaerobic conditions (free life) and in symbiosis with bean plants. The R. etli NifA-RpoN regulon was determined to contain 78 genes, including the genes involved in nitrogen fixation, and the analyses revealed 42 new NifA-RpoN-dependent genes. More importantly, this study demonstrated that the NifA-RpoN regulon is composed of genes and proteins that have very diverse functions, that play fundamental and previously less appreciated roles in regulating the normal physiology of the cell, and that have important functions in providing adequate conditions for efficient nitrogen fixation in symbiosis. The R. etli NifA-RpoN regulon defined here has some components in common with other NifA-RpoN regulons described previously, but the vast majority of the components have been found only in the R. etli regulon, suggesting that they have a specific role in this bacterium and particular requirements during nitrogen fixation compared with other symbiotic bacterial models.
PMID: 20453139 [PubMed - indexed for MEDLINE]
