http://www.biomedcentral.com/bmcmicrobiol/ The editor's pick of recent articles published by BMC Microbiology 2013-05-30T00:00:00Z Background: GTPases are the family of hydrolases that bind and hydrolyze guanosine triphosphate. The large Immunity-related GTPases and the small GTPase ADP-ribosylation factor-6 in host cells are known to accumulate on the parasitophorous vacuole membrane (PVM) of Toxoplasma gondii and play critical roles in this parasite infection, but these GTPases cannot explain the full extent of infection. Results: In this research, RhoA and Rac1 GTPases from the host cell were found to accumulate on the PVM regardless of the virulence of the T. gondii strains after T. gondii invasion, and this accumulation was dependent on their GTPase activity. The real-time micrography of T. gondii tachyzoites invading COS-7 cells overexpressing CFP-RhoA showed that this GTPase was recruited to the PVM at the very beginning of the invasion through the host cell membrane or from the cytosol. Host cell RhoA and Rac1 were also activated after T. gondii tachyzoites invasion, which was needed for host cell cytoskeleton reorganization to facilitate intracellular pathogens invasion. The decisive domains for the RhoA accumulation on the PVM included the GTP/Mg2+ binding site, the mDia effector interaction site, the G1 box, the G2 box and the G5 box, respectively, which were related to the binding of GTP for enzymatic activity and mDia for the regulation of microtubules. The recruited CFP-RhoA on the PVM could not be activated by epithelial growth factor (EGF) and no translocation was observed, unlike the unassociated RhoA in the host cell cytosol that migrated to the cell membrane towards the EGF activation spot. This result supported the hypothesis that the recruited RhoA or Rac1 on the PVM were in the GTP-bound active form. Wild-type RhoA or Rac1 overexpressed cells had almost the same infection rates by T. gondii as the mock-treated cells, while RhoA-N19 or Rac1-N17 transfected cells and RhoA, Rac1 or RhoA + Rac1 siRNA-treated cells showed significantly diminished infection rates compared to mock cells. Conclusions: The accumulation of the RhoA and Rac1 on the PVM and the requisite of their normal GTPase activity for efficient invasion implied their involvement and function in T. gondii invasion. http://www.biomedcentral.com/1471-2180/13/125 Ren-Hua Na Guo-Hui Zhu Ji-Xuan Luo Xiao-Jing Meng Liwang Cui Hong-Juan Peng Xiao-guang Chen Julian Gomez-Cambronero BMC Microbiology 2013, 13:125 2013-05-30T00:00:00Z 10.1186/1471-2180-13-125 Efficient invasion requires RhoA <p>RhoA and Rac1 GTPases are recruited from the host cell to accumulate on the parasite vacuole membrane (PVM) during invasion by <em>Toxplamsa gondii</em> tachyzoites and undergo activation which is required for efficient cell invasion by this parasite.</p> /content/figures/1471-2180-13-125-toc.gif BMC Microbiology 1471-2180 13 125 2013-05-30T00:00:00Z XML Background: Coccidioides immitis is a dimorphic fungus that causes disease in mammals, including human beings. It grows as a mycelium containing arthroconidia in the soil and in the host arthroconidia differentiates into a unique structure called a spherule. We used a custom open reading frame oligonucleotide microarray to compare the transcriptome of C. immitis mycelia with early (day 2) and late stage (day 8) spherules grown in vitro. All hybridizations were done in quadruplicate and stringent criteria were used to identify significantly differentially expressed genes. Results: 22% of C. immitis genes were differentially expressed in either day 2 or day 8 spherules compared to mycelia, and about 12% of genes were differentially expressed comparing the two spherule time points. Oxireductases, including an extracellular superoxide dismutase, were upregulated in spherules and they may be important for defense against oxidative stress. Many signal transduction molecules, including pleckstrin domain proteins, protein kinases and transcription factors were downregulated in day 2 spherules. Several genes involved in sulfur metabolism were downregulated in day 8 spherules compared to day 2 spherules. Transcription of amylase and alpha (1,3) glucan synthase was upregulated in spherules; these genes have been found to be important for differentiation to yeast in Histoplasma. There were two homologs of 4-hydroxyphenylpyruvate dioxygenase (4-HPPD); transcription of one was up- and the other downregulated. We tested the effect of a 4-HPPD inhibitor, nitisinone, on mycelial and spherule growth and found that it inhibited mycelial but not spherule growth. Conclusions: Transcription of many genes was differentially expressed in the process of arthroconidia to spherule conversion and spherule maturation, as would be expected given the magnitude of the morphologic change. The transcription profile of early stage (day 2) spherules was different than late stage (day 8) endosporulating spherules. In addition, very few genes that are important for spore to yeast conversion in other dimorphic fungi are differentially expressed in C. immitis mycelia and spherules suggesting that dimorphic fungi may have evolved different mechanisms to differentiate from mycelia to tissue invasive forms. http://www.biomedcentral.com/1471-2180/13/121 Suganya Viriyakosol Akul Singhania Joshua Fierer Jonathan Goldberg Theo N Kirkland Christopher Woelk BMC Microbiology 2013, 13:121 2013-05-28T00:00:00Z 10.1186/1471-2180-13-121 Conversion of Coccidioides <p>Mycelium to spherule conversion in <em>Coccidioides immitis</em> strains results in widespread transcriptional modulation, however many genes important for this process in other pathogenic fungi are not differentially expressed indicating the evolution of different mechanisms for this process</p> /content/figures/1471-2180-13-121-toc.gif BMC Microbiology 1471-2180 13 121 2013-05-28T00:00:00Z PDF Background: The bacterial surface protein internalin (InlA) is a major virulence factor of the food-born pathogen Listeria monocytogenes. It plays a critical role in the bacteria crossing the host intestinal barrier by a species-specific interaction with the cell adhesion molecule E-cadherin. In mice, the interaction of InlA with murine E-cadherin is impaired due to sequence-specific binding incompatibilities. We have previously used the approach of ‘murinisation’ to establish an oral listeriosis infection model in mice by exchanging two amino acid residues in InlA. This dramatically increases binding to mouse E-cadherin. In the present study, we have used bioluminescent murinised and non-murinised Listeria strains to examine the spatiotemporal dissemination of Listeria in four diverse mouse genetic backgrounds after oral inoculation. Results: The murinised Listeria monocytogenes strain showed enhanced invasiveness and induced more severe infections in all four investigated mouse inbred strains compared to the non-murinised Listeria strain. We identified C57BL/6J mice as being most resistant to orally acquired listeriosis whereas C3HeB/FeJ, A/J and BALB/cJ mice were found to be most susceptible to infection. This was reflected in faster kinetics of Listeria dissemination, higher bacterial loads in internal organs, and elevated serum levels of IL-6, IFN-γ, TNF-α and CCL2 in the susceptible strains as compared to the resistant C57BL/6J strain. Importantly, murinisation of InlA did not cause enhanced invasion of Listeria monocytogenes into the brain. Conclusion: Murinised Listeria are able to efficiently cross the intestinal barrier in mice from diverse genetic backgrounds. However, expression of murinized InlA does not enhance listerial brain invasion suggesting that crossing of the blood brain barrier and crossing of the intestinal epithelium are achieved by Listeria monocytogenes through different molecular mechanisms. http://www.biomedcentral.com/1471-2180/13/90 Silke Bergmann Philippa M Beard Bastian Pasche Stefan Lienenklaus Siegfried Weiss Cormac G M Gahan Klaus Schughart Andreas Lengeling BMC Microbiology 2013, 13:90 2013-04-23T00:00:00Z 10.1186/1471-2180-13-90 Internalin A murinisation allows dissemination <p><em>Listeria monocytogenes </em>modified to express a mutant internalin A, that interacts with murine E-cadherin, are able to efficiently cross the intestinal- but not the blood-brain barrier in mice suggesting different molecular mechanisms for these processes.</p> /content/figures/1471-2180-13-90-toc.gif BMC Microbiology 1471-2180 13 90 2013-04-23T00:00:00Z XML Background: Hfq is an RNA chaperone protein that has been broadly implicated in sRNA function in bacteria. Here we describe the construction and characterization of a null allele of the gene that encodes the RNA chaperone Hfq in Shewanella oneidensis strain MR-1, a dissimilatory metal reducing bacterium. Results: Loss of hfq in S. oneidensis results in a variety of mutant phenotypes, all of which are fully complemented by addition of a plasmid-borne copy of the wild type hfq gene. Aerobic cultures of the hfq∆ mutant grow more slowly through exponential phase than wild type cultures, and hfq∆ cultures reach a terminal cell density in stationary phase that is ~2/3 of that observed in wild type cultures. We have observed a similar growth phenotype when the hfq∆ mutant is cultured under anaerobic conditions with fumarate as the terminal electron acceptor, and we have found that the hfq∆ mutant is defective in Cr(VI) reduction. Finally, the hfq∆ mutant exhibits a striking loss of colony forming units in extended stationary phase and is highly sensitive to oxidative stress induced by H2O2 or methyl viologen (paraquat). Conclusions: The hfq mutant in S. oneidensis exhibits pleiotropic phenotypes, including a defect in metal reduction. Our results also suggest that hfq mutant phenotypes in S. oneidensis may be at least partially due to increased sensitivity to oxidative stress. http://www.biomedcentral.com/1471-2180/13/33 Christopher M Brennan Meghan L Keane Taylor M Hunt Matthew T Goulet Nicholas Q Mazzucca Zachary Sexton Taylor Mezoian Katherine E Douglas Jessica M Osborn Brett J Pellock BMC Microbiology 2013, 13:33 2013-02-08T00:00:00Z 10.1186/1471-2180-13-33 Hfq involved in oxidative stress response <p>Deletion of hfq, an RNA chaperone protein, in <em>Shewanella oneidensis</em> results in reduced growth rate and productivity of aerobic and anaerobic cultures, and compromises the bacterium&rsquo;s metal-reduction capability potentially due to an increased sensitivity to oxidative stress.</p> /content/figures/1471-2180-13-33-toc.gif BMC Microbiology 1471-2180 13 33 2013-02-08T00:00:00Z XML Background: Deviations in composition and diversity of intestinal microbiota in infancy have been associated with both the development and recurrence of atopic eczema. Thus, we decided to use a deep and global microarray-based method to characterize the diversity and temporal changes of the intestinal microbiota in infancy and to define specific bacterial signatures associated with eczema. Faecal microbiota at 6 and 18 months of age were analysed from 34 infants (15 with eczema and 19 healthy controls) selected from a prospective follow-up study based on the availability of faecal samples. The infants were originally randomized to receive either Lactobacillus rhamnosus GG or placebo. Results: Children with eczema harboured a more diverse total microbiota than control subjects as assessed by the Simpson’s reciprocal diversity index of the microarray profiles. Composition of the microbiota did not differ between study groups at age of 6 months, but was significantly different at age of 18 months as assessed by MCPP (p=0.01). At this age healthy children harboured 3 -fold greater amount of members of the Bacteroidetes (p=0.01). Microbiota of children suffering from eczema had increased abundance of the Clostridium clusters IV and XIVa, which are typically abundant in adults. Probiotic Lactobacillus rhamnosus GG supplementation in early infancy was observed to have minor long-term effects on the microbiota composition. Conclusion: A diverse and adult-type microbiota in early childhood is associated with eczema and it may contribute to the perpetuation of eczema. http://www.biomedcentral.com/1471-2180/13/12 Lotta Nylund Reetta Satokari Janne Nikkilä Mirjana Rajilić-Stojanović Marko Kalliomäki Erika Isolauri Seppo Salminen Willem M de Vos BMC Microbiology 2013, 13:12 2013-01-23T00:00:00Z 10.1186/1471-2180-13-12 Gut microbes linked to eczema <p>Children with eczema harbour a greater diversity of microbes in the gut than those without, including an increased abundance of bacteria that are typically more common in adults, which may contribute to the perpetuation of the condition.</p> /content/figures/1471-2180-13-12-toc.gif BMC Microbiology 1471-2180 13 12 2013-01-23T00:00:00Z XML Bacterial cultivation requires consideration of three things: The bacterial strain, cultivation medium, and cultivation conditions. Most microbiologists dutifully report their choice of strains and cultivation media in manuscripts; however, these same microbiologists often overlook reporting cultivation conditions. Without this information, it is difficult to determine if cultures were grown aerobically, microaerobically, or anaerobically. To cultivate bacteria aerobically, it is necessary to understand that oxygen does not readily diffuse into culture media; it needs help to get in. Microbiologists can do this by altering the flask-to-medium ratio, rpm of agitation, and/or the concentration of atmospheric oxygen, or by using baffled flasks. http://www.biomedcentral.com/1471-2180/13/9 Greg A Somerville Richard A Proctor BMC Microbiology 2013, 13:9 2013-01-16T00:00:00Z 10.1186/1471-2180-13-9 Culture conditions still relevant <p>As laboratory technology increases in sophistication Greg Somerville and Richard Proctor highlight the importance of considering all bacterial culture conditions, such as the flask-to-medium ratio, when designing experiments, to ensure accuracy in the reporting of results.</p> /content/figures/1471-2180-13-9-toc.gif BMC Microbiology 1471-2180 13 9 2013-01-16T00:00:00Z XML