Erratum: An ffh mutant of Streptococcus mutans is viable and able to physiologically adapt to low pH in continuous culture (FEMS Microbiology Letters (2004) 234 (315-324) PII: S0378109704002423 DOI: 10.1016/j.femsle.2004.03.043)

[No abstract available]Erratu

An ffh mutant of Streptococcus mutans is viable and able to physiologically adapt to low pH in continuous culture

Previously, we described in Streptococcus mutans strain NG8 a 5-gene operon (sat) that includes ffh, the bacterial homologue of the eukaryotic signal recognition particle (SRP) protein, SR54. A mutation in ffh resulted in acid sensitivity but not loss of viability. In the present study, chemostat-grown cells of the ffh mutant were shown to possess only 26% and 39% of the parental membrane F-ATPase activity and 55% and 75% of parental glucose- phosphotransferase (PTS) activity when pH-7 and pH-5-grown cells, respectively, were assayed. Two-dimensional-gel electrophoretic analyses revealed significant differences in protein profiles between parent and ffh-mutant strains at both pH 5 and pH 7. It appears that the loss of active SRP (Ffh) function, while not lethal, results in substantial alterations in cellular physiology that includes acid tolerance. © 2004 Federation of European Microbiological Societies. Published by Elsevier B.V. All rights reserved.Articl

The influence of two PBL curricular contexts on first-year students' understandings of PBL, approaches to learning and outcomes

PBL curricular design aims to support students to think and act as practitioners. Therefore, students need to understand the learning context as it is designed. First-year dental students’ understandings of PBL, learning approaches, and student performance at Malmö University and the University of Adelaide were investigated. Students’ understandings of PBL in both curricula developed over one semester to more closely align with planned intentions. However, several key features of PBL were not noted by students. Malmö students’ PBL experiences were associated with deep approaches while Adelaide students’ PBL experiences were associated with a decrease in deep approaches. Associations between PBL understandings, approaches, and performance were not evident. These findings highlight the complex interactions between PBL contexts and students’ responses and provide some insights into curricular designs that support development of students’ understandings of PBL and associated learning outcomes.Tracey Winning, Vicki Skinner, Angela Kinnell, Grant Townsend, Gunnel Svensäter, Madeleine Rohlin and Julia Davie

Effect of acid shock on protein expression by biofilm cells of Streptococcus mutans

Streptococcus mutans is a component of the dental plaque biofilm and a major causal agent of dental caries. Log-phase cells of the organism are known to induce an acid tolerance response (ATR) at sub-lethal pH values ( approximately 5.5) that enhances survival at lower pH values such as those encountered in caries lesions. In this study, we have employed a rod biofilm chemostat system to demonstrate that, while planktonic cells induced a strong ATR at pH 5.5, biofilm cells were inherently more acid resistant than such cells in spite of a negli-gible induction of an ATR. Since these results suggested that surface growth itself triggered an ATR in biofilm cells, we were interested in comparing the effects of a pH change from 7.5 to 5.5 on protein syn-thesis by the two cell types. For this, cells were pulse labeled with [(14)C]-amino acids following the pH change to pH 5.5, the proteins extracted and separated by two-dimensional (2D) electrophoresis fol-lowed by autoradiography and computer-assisted image analysis. A comparison between the cells incubated at pH 5.5 and the control biofilm cells revealed 23 novel proteins that were absent in the control cells, and 126 proteins with an altered relative rate of synthesis. While the number of changes in protein expression in the biofilm cells was within the same range as for planktonic cells, the magnitude of their change was significantly less in biofilm cells, supporting the observa-tion that acidification of biofilm cells induced a negligible ATR. Mass spectrometry and computer-assisted protein sequence analysis revealed that ATR induction of the planktonic cells resulted in the downregula-tion of glycolytic enzymes presumably to limit cellular damage by the acidification of the external environment. On the other hand, the gly-colytic enzymes in control biofilm cells were significantly less down-regulated and key enzymes, such as lactate dehydrogenase were upregulated during pH 5.5 incubation, suggesting that the enhanced acid resistance of biofilm cells is associated with the maintenance of pH homeostasis by H+ extrusion via membrane ATPase and increased lactate efflux