A Quantitative Study of Calcium Binding and Aggregation in Selected Oral Bacteria

Abstract

By means of micro-equilibrium dialysis, calcium binding capacities and affinities were measured in three different oral bacteria, and the effects of extracellular polysaccharide, pH, and aggregation were investigated. Binding capacities of 31.0 +/- 2.1 (C. matruchotii), 34.7 +/- 3.7 (S. sanguis), and 41.5 +/- 5.4 (S. downei) mumol calcium/g wet weight of cells were found at pH 7.0, falling to 21.4 +/- 0.8 mumol calcium/g wet wt. cells at pH 5.0 for S. downei. Dissociation constants were found to vary between 0.78 +/- 0.24 and 1.77 +/- 0.30 mmol/L (at pH 7.0, depending on species), and between 0.62 +/- 0.04 and 1.77 +/- 0.30 (in the pH range 5.0 to 7.0, for S. downei only). Examination suggested that at pH 7.0 calcium-facilitated bacterial association occurs in the streptococci with calcium uptake curves analogous with those of positively cooperative systems. Desorption of calcium from aggregated S. downei suggested that the mechanism of desorption differed from that of uptake. This may be an important factor in plaque formation and in the binding of cells to the surface of formed plaque. Plaque calcium forms a reservoir, readily released by a pH drop, which may increase plaque fluid saturation and reduce demineralization.

Calcium binding to S. mutans grown in the presence or absence of sucrose

“…2 Also, the lower protein concentration in bacterial pellets (Table 1) is in agreement with van Houte et al, 8 who reported decreased bacterial cell density when this S. mutans strain was grown in THB supplemented with 2% sucrose as compared to the same medium with a ten times lower concentration. Considering that proteins from bacterial cell walls are Ca-binding sites, 20 and EPS does not have this property, 9 it would be expected that bacterial pellets grown in the presence of sucrose would have a lower ability to bind Ca per weight of bacteria. Although this was observed for the baseline Ca concentration in the bacterial pellets (Table 1), the results of Ca binding after treatment with Ca-containing solutions did not support this hypothesis (Figure 1), and the theoretical support to explain these results is presented below.…”

“…In order to remove remnants of culture broth and unbound Ca, the pellets were sequentially washed using sonication (Vibra Cell sonicator, Sonics and Materials, Danbury, USA) at 7 W for 1 min, first in 0.05 M PIPES buffer, pH 7.0, followed by 0.01 M EDTA solution, and again in PIPES buffer. 9 Between each washing, the pellet was recovered by centrifugation. After this procedure, the pellet was spread on filter paper to remove excess moisture.…”

“…4 In addition, they change the biofilm structure, resulting in increased porosity, 5 which allows fermentable substrates to diffuse and be metabolized in the deepest parts of the biofilm. 6 Furthermore, since IEPS decrease the bacterial density of biofilms, 7,8 they may reduce the amount of biofilm calcium (Ca) binding sites 9 , which could also influence biofilm cariogenicity. Ca bound to bacterial cell Declaration of Interests: The authors certify that they have no commercial or associative interest that represents a conflict of interest in connection with the manuscript.…”

“…walls might function as a source of mineral ions to the biofilm fluid during a pH drop, 9 acting as a mineral buffer by helping to maintain the saturation of plaque fluid with respect to tooth mineral, a factor that largely governs its dissolution. 10 Therefore, we hypothesized that the number of binding sites for Ca would be reduced in dental biofilm formed in the presence of sucrose, and we investigated this effect by evaluating the rate of Ca binding to S. mutans grown in the presence of sucrose or its component monosaccharides in vitro.…”

A calcium signal is involved in heterocyst differentiation in the cyanobacterium Anabaena sp. PCC7120

“…Since Ca 2+ was first studied in bacteria fifty years ago (Norris & Jensen, 1957) it has been implicated in a broad range of physiological processes in prokaryotes that include chemotaxis and motility (Tisa & Adler, 1992Watkins et al, 1995;Pitta et al, 1997), pathogenesis (Rose et al, 1993;Straley et al, 1993), the cell cycle and the control of the initiation of replication (Jiménez-Sanchez et al, 1993;Yu & Margolin, 1997), quorum sensing (Wherten & Lundgren, 2001) and spore and fruiting body formation (Inouye et al, 1983;O'Hara & Hageman, 1990). In many cases, the involvement of Ca 2+ in the regulation of cellular processes has been roughly described in terms of an influx or efflux of Ca 2+ from the cytosol.…”