title: Acid tolerance of Streptococcus macedonicus as assessed by flow cytometry and single-cell sorting.
abstract: An in situ flow cytometric viability assay employing carboxyfluorescein diacetate and propidium iodide was used to identify Streptococcus macedonicus acid tolerance phenotypes. The logarithmic-phase acid tolerance response (L-ATR) was evident when cells were (i) left to autoacidify unbuffered medium, (ii) transiently exposed to nonlethal acidic pH, or (iii) systematically grown under suboptimal acidic conditions (acid habituation). Stationary-phase ATR was also detected; this phenotype was gradually degenerated while cells resided at this phase. Single-cell analysis of S. macedonicus during induction of L-ATR revealed heterogeneity in both the ability and the rate of tolerance acquisition within clonal populations. L-ATR was found to be partially dependent on de novo protein synthesis and compositional changes of the cell envelope. Interestingly, acid-habituated cells were interlaced in lengthier chains and exhibited an irregular pattern of active peptidoglycan biosynthesis sites when probed with BODIPY FL vancomycin. L-ATR caused cells to retain their membrane potential after lethal challenge, as judged by ratiometric analysis with oxonol [DiBAC(4)(3)]. Furthermore, F-ATPase was important during the induction of L-ATR, but in the case of a fully launched response, inhibition of F-ATPase affected acid resistance only partially. Activities of both F-ATPase and the glucose-specific phosphoenolpyruvate-dependent phosphotransferase system were increased after L-ATR induction, distinguishing S. macedonicus from oral streptococci. Finally, the in situ viability assessment was compared to medium-based recovery after single-cell sorting, revealing that the culturability of subpopulations with identical fluorescence characteristics is dependent on the treatments imposed to the cells prior to acid challenge.
authors.affiliation: Laboratory of Dairy Research, Department of Food Science and Technology, Agricultural University of Athens, Iera Odos 75, 118 55 Athens, Greece.
authors.forename: Konstantinos
authors.initials: K
authors.lastname: Papadimitriou
authors.forename: Harris
authors.initials: H
authors.lastname: Pratsinis
authors.forename: Gerhard
authors.initials: G
authors.lastname: Nebe-von-Caron
authors.forename: Dimitris
authors.initials: D
authors.lastname: Kletsas
authors.forename: Effie
authors.initials: E
authors.lastname: Tsakalidou
mesh_terms: D000222:Adaptation, Physiological; D002473:Cell Wall / Q000378:metabolism; D005434:Flow Cytometry; D005452:Fluoresceins; D005456:Fluorescent Dyes; D006863:Hydrogen-Ion Concentration; D010641:Phenotype; D011419:Propidium; D013291:Streptococcus / Q000166:cytology / Q000254:growth & development* / Q000502:physiology*
chemical_list: D005452:Fluoresceins; D005456:Fluorescent Dyes; C027780:carboxyfluoresceindiacetate; D011419:Propidium