Role of the Streptococcus mutans CRISPR-Cas systems in immunity and cell physiology.

CRISPR-Cas systems provide adaptive microbial immunity against invading viruses and plasmids. The cariogenic bacterium Streptococcus mutans UA159 has two CRISPR-Cas systems: CRISPR1 (type II-A) and CRISPR2 (type I-C) with several spacers from both CRISPR cassettes matching sequences of phage M102 or genomic sequences of other S. mutans. The deletion of the cas genes of CRISPR1 (ΔC1S), CRISPR2 (ΔC2E), or both CRISPR1+2 (ΔC1SC2E) or the removal of spacers 2 and 3 (ΔCR1SP13E) in S. mutans UA159 did not affect phage sensitivity when challenged with virulent phage M102. Using plasmid transformation experiments, we demonstrated that the CRISPR1-Cas system inhibits transformation of S. mutans by the plasmids matching the spacers 2 and 3. Functional analysis of the cas deletion mutants revealed that in addition to a role in plasmid targeting, both CRISPR systems also contribute to the regulation of bacterial physiology in S. mutans. Compared to wild-type cells, the ΔC1S strain displayed diminished growth under cell membrane and oxidative stress, enhanced growth under low pH, and had reduced survival under heat shock and DNA-damaging conditions, whereas the ΔC2E strain exhibited increased sensitivity to heat shock. Transcriptional analysis revealed that the two-component signal transduction system VicR/K differentially modulates expression of cas genes within CRISPR-Cas systems, suggesting that VicR/K might coordinate the expression of two CRISPR-Cas systems. Collectively, we provide in vivo evidence that the type II-A CRISPR-Cas system of S. mutans may be targeted to manipulate its stress response and to influence the host to control the uptake and dissemination of antibiotic resistance genes.

Ultra high efficiency/low pressure supercritical fluid chromatography with superficially porous particles for triglyceride separation.

This paper reports the development of the separation of vegetable oil triglycerides (TG) in supercritical chromatography (SFC), using superficially porous particles (SPPs). The SPP, having a small diameter (2-3µm), provide a higher theoretical plate number (N), which allows to improve separation of critical pairs of compounds. However, compared to fully porous particles of larger diameter (5µm), the pressure drop is also increased. Fortunately, supercritical fluids have a low viscosity, which allows coupling several columns to achieve high N values, while maintaining flow rate above 1ml/min, ensuring a ultra high efficiency (UHE) at low pressure (LP) (below 40MPa), with regards to the one reached with liquid and sub-two micron particles (around 100MPa). The use of two detector systems (UV and ELSD) connected in series to the UHE-LP-SFC system provides complementary responses, due to their specific detection principles. Working in a first part with three coupled Kinetex C18 columns (45cm total length), the effect of modifier nature and percentage were studied with two reference oils, argan and rapeseed, chosen for their different and well-known TG composition. The analytical method was developed from previous studies performed with fully porous particles (FPP). Optimized conditions with three Kinetex were as follows: 17°C, 12% of ACN/MeOH (90/10; v/v). With these conditions, and by using an increased length of Kinetex C18 column (60cm), another additional column was selected from ten different commercial SPP C18 bonded phases, by applying a Derringer function on varied parameters: theoretical plate number (TPN), separation index (SI) for critical pairs of peaks (the peaks of compounds difficult to separate due to subtle structural differences), the analysis duration, and the total peak number. This function normalizes the values of any parameters, between 0 and 1, from the worst value to the better, allowing to take account of various parameters in the final choice. Finally, by using four Kinetex C18 plus one Accucore C18 (75cm total column length), a high-performance separation of triglycerides was achieved, with reasonable analysis duration and isocratic conditions. These conditions can be applied to varied vegetable oils. Identification of the numerous separated peaks of rapeseed oil was achieved by using published data and chromatographic retention behaviour.

Uptake of immune RNA by normal mouse spleen cells.

Normal mouse spleen cells take up in vitro radioactively labeled immune RNA. RNA taken up is present in nuclei, polysomes, membranes and cytoplasm. About 20-40% of immune RNA is nonspecifically associated with cell surface. 45% of RNA taken up is degraded and reutilized inside the cells within 2 hours.

Studies of interaction of immune RNA with normal spleen cells.

Normal mouse spleen cells incorporate in vitro radioactively labeled immune RNA. At saturation, 10(6) cells incorporate about 6 X 10(16) daltons of this RNA. Immune RNA is incorporated in two times greater amounts than control RNA. Maximum incorporation is observed in the first few minutes of incubation. Immune RNA incorporated by spleen cells is present both in cytoplasm and nuclei. Protamine sulphate has stimulatory effect on immune RNA incorporation. Actinomycin D does not affect incorporation of immune RNA.