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For the next session (Tuesday 4th March, 8pm GMT) we will be discussing the following paper: Effect of spaceflight on Pseudomonas aeruginosa final cell density is modulated by nutrient and oxygen availability available from the following link


Background: Abundant populations of bacteria have been observed on Mir and the International Space Station.
While some experiments have shown that bacteria cultured during spaceflight exhibit a range of potentially
troublesome characteristics, including increases in growth, antibiotic resistance and virulence, other studies have
shown minimal differences when cells were cultured during spaceflight or on Earth. Although the final cell density
of bacteria grown during spaceflight has been reported for several species, we are not yet able to predict how
different microorganisms will respond to the microgravity environment. In order to build our understanding of how
spaceflight affects bacterial final cell densities, additional studies are needed to determine whether the observed
differences are due to varied methods, experimental conditions, or organism specific responses.

Results: Here, we have explored how phosphate concentration, carbon source, oxygen availability, and motility
affect the growth of Pseudomonas aeruginosa in modified artificial urine media during spaceflight. We observed
that P. aeruginosa grown during spaceflight exhibited increased final cell density relative to normal gravity controls
when low concentrations of phosphate in the media were combined with decreased oxygen availability. In
contrast, when the availability of either phosphate or oxygen was increased, no difference in final cell density was
observed between spaceflight and normal gravity. Because motility has been suggested to affect how microbes
respond to microgravity, we compared the growth of wild-type P. aeruginosa to a ΔmotABCD mutant deficient in
swimming motility. However, the final cell densities observed with the motility mutant were consistent with those
observed with wild type for all conditions tested.

Conclusions: These results indicate that differences in bacterial final cell densities observed between spaceflight and
normal gravity are due to an interplay between microgravity conditions and the availability of substrates essential for
growth. Further, our results suggest that microbes grown under nutrient-limiting conditions are likely to reach higher cell
densities under microgravity conditions than they would on Earth. Considering that the majority of bacteria inhabiting
spacecrafts and space stations are likely to live under nutrient limitations, our findings highlight the need to explore the
impact microgravity and other aspects of the spaceflight environment have on microbial growth and physiology

Discussion points?

Was the paper well written?
Were the methods used appropiate?
Were the experiments carried out adequately?
What else can be done?

In Tuesday’s #microtwjc we will be discussing viral miRNAs:

Zhang S, Sroller V, Zanwar P, Chen CJ, Halvorson SJ, et al. (2014) Viral MicroRNA Effects on Pathogenesis of Polyomavirus SV40 Infections in Syrian Golden Hamsters. PLoS Pathog 10(2): e1003912. doi:10.1371/journal.ppat.1003912


Effects of polyomavirus SV40 microRNA on pathogenesis of viral infections in vivo are not known. Syrian golden hamsters are the small animal model for studies of SV40. We report here effects of SV40 microRNA and influence of the structure of the regulatory region on dynamics of SV40 DNA levels in vivo. Outbred young adult hamsters were inoculated by the intracardiac route with 1×107 plaque-forming units of four different variants of SV40. Infected animals were sacrificed from 3 to 270 days postinfection and viral DNA loads in different tissues determined by quantitative real-time polymerase chain reaction assays. All SV40 strains displayed frequent establishment of persistent infections and slow viral clearance. SV40 had a broad tissue tropism, with infected tissues including liver, kidney, spleen, lung, and brain. Liver and kidney contained higher viral DNA loads than other tissues; kidneys were the preferred site for long-term persistent infection although detectable virus was also retained in livers. Expression of SV40 microRNA was demonstrated in wild-type SV40-infected tissues. MicroRNA-negative mutant viruses consistently produced higher viral DNA loads than wild-type SV40 in both liver and kidney. Viruses with complex regulatory regions displayed modestly higher viral DNA loads in the kidney than those with simple regulatory regions. Early viral transcripts were detected at higher levels than late transcripts in liver and kidney. Infectious virus was detected infrequently. There was limited evidence of increased clearance of microRNA-deficient viruses. Wild-type and microRNA-negative mutants of SV40 showed similar rates of transformation of mouse cells in vitro and tumor induction in weanling hamsters in vivo. This report identified broad tissue tropism for SV40 in vivo in hamsters and provides the first evidence of expression and function of SV40 microRNA in vivo. Viral microRNA dampened viral DNA levels in tissues infected by SV40 strains with simple or complex regulatory regions.

Author’s Summary:

The recent discovery of virally encoded microRNAs (miRNAs) raises the possibility of additional regulatory processes being involved in viral replication, immune recognition, and host cell survival. In this study, we sought to characterize the effect of SV40-encoded miRNAs and the structure of the viral regulatory region on infections in outbred Syrian golden hamsters. Results revealed that SV40 has a wide tissue tropism, including liver, kidney, spleen, lung, and brain, with kidney the preferred site for long-term persistent infection. Significant increases in tissue-associated viral DNA loads were observed with miRNA-negative mutant strains, whereas the presence of SV40 miRNAs had no effect on tumor induction and little effect on viral clearance. Our results provide the first evidence for SV40 miRNA expression and function in an in vivoanimal model and highlight the complexity of regulation of SV40 viral replication and persistent infections.

Discussion points

  1. Was the paper well written etc?
  2. Were all of the methods appropriate?  Were there any experiments missing that you think needed to be there?
  3. What future work would you like to see done?

Hope to see you there, Tues 18th Feb at 8pm GMT

Morning All,

Apologies for the late posting of this paper. For the upcoming #MicroTwJc (8pm GMT, Tuesday 4th February 2014) we will be following (quite literally) Pseudomonas aeruginosa cells as they try and move around in their environment.  This newly relaxed paper was chosen because 1) it uses holographic tracking which is and sounds very cool, and 2) I couldn’t find any newly released rugby-microbiology hybrid papers (to commemorate the start of the six nations! – which is a shame, however there is a nice elite rugby cryotherapy paper out there).

Citation: Vater SM, Weiße S, Maleschlijski S, Lotz C, Koschitzki F, et al. (2014) Swimming Behavior of Pseudomonas aeruginosa Studied by Holographic 3D Tracking. PLoS ONE 9(1): e87765. doi:10.1371/journal.pone.0087765

Authors: Svenja M. Vater, Sebastian Weiße, Stojan Maleschlijski1, Carmen Lotz, Florian Koschitzki, Thomas Schwartz, Ursula Obst, Axel Rosenhahn

Title: Swimming Behavior of Pseudomonas aeruginosa Studied by Holographic 3D Tracking

Abstract: Holographic 3D tracking was applied to record and analyze the swimming behavior ofPseudomonas aeruginosa. The obtained trajectories allow to qualitatively and quantitatively analyze the free swimming behavior of the bacterium. This can be classified into five distinct swimming patterns. In addition to the previously reported smooth and oscillatory swimming motions, three additional patterns are distinguished. We show that Pseudomonas aeruginosaperforms helical movements which were so far only described for larger microorganisms. Occurrence of the swimming patterns was determined and transitions between the patterns were analyzed.

Discussion Points:

  • Was the paper clearly written?
  • Were the methods chosen appropriate?
  • Do the experiments show sufficient proof for the claim that transcriptional regulation is not sufficient to explain flux changes?
  • What experiments could be done next?



See you all on Tuesday! Go Wales!