Extracellular Polysaccharide Synthesis Research Articles

Fractionation of the β-Linked Glucans of Bradyrhizobium japonicum and Their Response to Osmotic Potential

Bradyrhizobium japonicum USDA 110 synthesized both extracellular and periplasmic polysaccharides when grown on mannitol minimal medium. The extracellular polysaccharides were separated into a high-molecular-weight acidic capsular extracellular polysaccharide fraction (90% of total hexose) and three lower-molecular-weight glucan fractions by liquid chromatography. Periplasmic glucans, extracted from washed cells with 1% trichloroacetic acid, gave a similar pattern on liquid chromatography. Linkage analysis of the major periplasmic glucan fractions demonstrated mainly 6-linked glucose (63 to 68%), along with some 3,6- (8 to 18%), 3- (9 to 11%), and terminal (7 to 8%) linkages. The glucose residues were beta-linked as shown by H-nuclear magnetic resonance analysis. Glucan synthesis by B. japonicum cells grown on mannitol medium with 0 to 350 mM fructose as osmolyte was measured. Fructose at 150 mM or higher inhibited synthesis of periplasmic and extracellular 3- and 6-linked glucans but had no effect on the synthesis of capsular acidic extracellular polysaccharides.

ThercsAGene fromErwinia amylovora: Identification, Nucleotide Sequence, and Regulation of Exopolysaccharide Biosynthesis

RcsA is a positive activator of extracellular polysaccharide synthesis in the Enterobacteriaceae. A cosmid clone containing the rcsA gene from Erwinia amylovora was identified by its ability to restore mucoidy to an E. stewartii rcsA mutant. The rcsA gene was subcloned on a 2.2-kilobase HindIII-PstI fragment that hybridized with an E. stewartii rcsA probe and complemented E. stewartii and Escherichia coli rcsA mutants. In addition, the cloned E. amylovora rcsA gene stimulated expression of cps::lac fusions in E. coli and E. stewartii. The rcsA region was sequenced, and one open reading frame of 211 amino acids was found. The predicted protein sequence specified by this open reading frame was 55% homologous with that of the Klebsiella pneumoniae RcsA protein. Highly conserved regions in the 3' and 5' ends of the two proteins were observed. An E. amylovora rcsA mutant was constructed by Tn5 mutagenesis of the cloned gene followed by recombination of the mutation into the chromosome of wild-type strain Ea1/79. The synthesis of both amylovorin and levan was reduced by more than 90% in this mutant, indicating common regulation of the two polysaccharides by rcsA. Virulence of the rcsA mutant on immature pear fruit was diminished but not completely abolished.

The 29 kb Plasmid, Common in Strains of Erwinia amylovora, Modulates Development of Fireblight Symptoms

To cure the fireblight pathogen Erwinia amylovora of a 29 kb plasmid (pEA29) that is common in strains of these bacteria, restriction fragments of this plasmid were inserted into plasmids based on replication functions of bacteriophage fd, which cannot replicate in bacteria without expression of viral gene 2-protein. A 4·4 kb PstI fragment including the unique BamHI site of pEA29 allowed pfd plasmids to be propagated in E. amylovora. Furthermore, selection for these plasmids removed the natural 29 kb plasmid, apparently because of plasmid incompatibility. The pfd plasmids with the 4·4 kb insertion had a high tendency to segregate in E. amylovora when grown without selective pressure. Plasmid-free E. amylovora strains were virulent in standard tests on slices of immature pears, but symptom development was delayed compared to the wild-type. When assayed on pear seedlings a deficiency in pathogenicity was observed. Furthermore, strains without pEA29 spread more slowly on a lawn of pear cells than did wild-type strains. Plasmid-free strains of E. amylovora were not auxotrophic, but synthesis of extracellular polysaccharide was altered under certain growth conditions.

Occurrence and transport of particle “tetrads” in the cell membranes of the unicellular red alga porphyridium visualized by freeze-fracture

The supramolecular organization of biomembranes in the unicellular red algae Porphyridium cruentum and Porphyridium aerugineum is studied in replicas of rapidly frozen and fractured cells. Intramembrane particle complexes composed of four particles (“tetrads”, average diameter 9 nm) have been observed in the protoplasmic fracture (PF) face of the plasma membrane, Golgi cisternae, and Golgi-derived vesicles. The occurrence of particle tetrads in the Golgi cisternae and vesicles suggests that the Golgi complex is responsible for the selective transport and exocytosis of tetrads in the red algaPorphyridium, as has been previously indicated for rosettes of six particles in the algaMicrasterias (T. H. Giddings, Jr., D. L. Brower, and L. A. Staehelin (1980)J. Cell Biol.84, 327–339) and in higher plants (C. H. Haigler and R. M. Brown, Jr. (1986)Protoplasma134, 111–120). The plasma membrane exhibits two distinct populations of intramembrane particles (with diameters between 8.5 and 9.5 nm and between 10.5 and 11.5 nm, respectively). The tetrad frequency varies between 16 and 33 μm−2. The particle density of the PF face of the plasma membrane is 2400 μm−2, while that of the exoplasmic face is 260 μm−2. Considering that the Golgi complex is involved in the synthesis and export of cell surface polysaccharides in the red algaPorphyridium (J. Ramus (1972)J. Phycol.8, 97–111;J. Ramus and D. M. Robins (1975)J. Phycol.11, 70–74;L. V. Evans, M. E. Callow, E. Percival, and V. Farreed (1974)J. Cell Sci.16, 1–21;I. Tsekos (1985)Protoplasma129, 127–136) it could be assumed that the tetrads represent a membrane-bound multienzyme complex participating in the synthesis of extracellular polysaccharides.

Bacterial extracellular polysaccharides.

The synthesis of extracellular polysaccharides has been recognized in certain bacterial cultures since the 1880s. It is now apparent that a wide range of bacteria produce these polymers and an equally wide range of chemical structures are possible. Their surface location, together with the range of available monosaccharide combinations, noncarbohydrate substituents, and linkage types, make extracellular polysaccharides excellent agents of diversity. As a result, much effort has been directed towards elucidating their structure in pathogenic bacteria and in enteric organisms in particular. Commercial applications of microbial polysaccharides have now broadened the scope of structural information. Most recently, technological advances in molecular biology have created the possibility of manipulating desired polymer characteristics, and with these advances, our knowledge of the mechanisms of synthesis and regulation of cell surface polysaccharides has improved. Ultimately more information regarding the function of extracellular polysaccharides in natural environments may result.

Control of extracellular polysaccharide synthesis in Erwinia stewartii and Escherichia coli K-12: a common regulatory function.

A primary determinant of pathogenicity in Erwinia stewartii is the production of extracellular polysaccharide (EPS). A single mutation can abolish both EPS synthesis and pathogenicity; both properties are restored by a single cosmid clone. Subcloning and insertion analysis have defined a single positive regulatory function which shares a number of similarities with the rcsA function of Escherichia coli K-12, a positive regulator for capsular polysaccharide synthesis. In E. stewartii, the gene promotes the transcription of at least two operons (cps) involved in EPS synthesis; we have previously demonstrated a similar function for rcsA in E. coli. Both genes code for proteins of 25 to 27 kilodaltons; both proteins are unstable in E. coli. The E. stewartii RcsA protein was stabilized in E. coli lon mutants, as the RcsA product from E. coli is. The E. stewartii function complemented E. coli rcsA mutants, and the E. coli RcsA function increased cps expression and restored virulence in E. stewartii mutants. Therefore, these two gram-negative organisms share a similar component of their regulatory circuitry for the control of capsular polysaccharide synthesis.

Inhibition of fireblight disease by injection of D-galactose or L-fucose into susceptible apple plants

The colonization of 1-year-old apple plants (cv. M26) by Erwinia amylovora (Burrill) Winslow was arrested by the administration of D-galactose or L-fucose solution to the plants. Treatment started 24 h before inoculation of shoot tips with bacteria, and was continued for 8–14 days. Solutions were administered via three debladed leaf midribs adjacent to the site of inoculation, or by gravity injection into the woody stem. Inoculated plants taking up 0·6% w v D-galactose solution via the petioles (mean rate per plant 3·8 ml day −1 for 8 days) showed inhibition of disease. Similar uptake of water, 0·6% w v sucrose, D-mannose or sorbitol had no effect. Treatment with 0·6% w v D-galactose was not effective when uptake per plant was less than approximately 2 ml day −1, at which rate 0·6% w v L-fucose inhibited the disease. Stem-injection of 1·2% w v D-galactose (mean rate per plant 12 ml day −1 for 4 days) inhibited the disease but caused abscission of the lower mature leaves and immature leaf curl. Stem-injection of 1·2% w v D-galactose (mean 10·4 ml per plant) for 24 h followed by continuous stem-injection of 0·6% w v D-galactose (mean rate per plant 5·7 ml day −1 for 5 days) also inhibited the disease and did not cause visible leaf reactions. Simultaneous stem and petiole injection of 0·6% w v L-fucose (mean total rate per plant 4·9 ml day −1 for 4 days) similarly inhibited the disease without causing visible leaf damage. Treated plants showing disease inhibition developed significantly more shoots from lateral buds than did untreated inoculated plants. Very little or no bacterial ooze was exuded by inoculated plants successfully treated with D-galactose of L-fucose, but D-galactose, D-glucose and L-fucose allowed the synthesis of extracellular polysaccharide in bacterial cultures containing sorbitol, a host-plant carbohydrate. Heavily capsulated cells similar to those found in infected plants were produced in cultures containing D-galactose. Bacteria grown in the presence of L-fucose were only moderately capsulated. The outer surface component lipopolysaccharide produced by E. amylovora contains D-fucose. It is suggested that D-galactose and L-fucose caused changes in the outer surface components of bacteria in treated plants, and that such changes inhibited the disease by interfering with reactions at the host-pathogen interface.

Glycogen Metabolism in Aureobasidium Pullulans: A Glycogen Synthetase with Unusual Activation Properties

(1987). Glycogen Metabolism in Aureobasidium Pullulans: A Glycogen Synthetase with Unusual Activation Properties. Critical Reviews in Biotechnology: Vol. 5, No. 3, pp. 185-193.

Molecular cloning of virulence genes from Erwinia stewartii.

A library of Erwinia stewartii DNA was constructed in cosmid pVK100 and used to complement spontaneous and Mu pf7701-induced (designated by the prefix MU) avirulent mutants. Plasmid pES4507 restored water-soaking ability and extracellular polysaccharide (EPS) synthesis to mutants MU14110 and MU2B70 (group I); pES1044 restored water-soaking ability to MU43, MU51, MU136, MU141, and RDF6011 (group II); and pES2144 complemented four spontaneous EPS- mutants (group III). Hybridization of labeled plasmid DNA to Southern blots of genomic DNA from the mutants revealed that a Mu pf7701 insertion was associated with the respective cloned region in all mutants except MU2B70 and MU223. In these strains, the plasmid may be suppressing the avirulent phenotype rather than complementing the mutation.

Effects of Dietary Carbohydrates on the Numbers of Streptococcus mutans and Actinomyces viscosus in Dental Plaque of Mono-infected Gnotobiotic Rats

Dietary sucrose and glucose are known to promote the accumulation of, respectively, Streptococcus mutans and Actinomyces viscosus in complex dental plaque microflora. In this study, we have investigated the effects of these carbohydrates on the numbers of S. mutans and A. viscosus colonizing the teeth of mono-infected gnotobiotic rats. Sucrose at a dietary concentration of between 0.25 and 0.5 percent (corresponding with 7-15 mM in the drinking water) caused an increase in the numbers of S. mutans. This result strongly suggested that the increase was due to extracellular polysaccharide (EPS) synthesis by glucosyltransferase, whose Km value (1.0-7.0 mM) is in the same concentration range. The numbers of A. viscosus increased three-fold when 10% glucose was added to the basal diet. It seems plausible that this was due to extracellular heteropolysaccharide produced by A. viscosus in the presence of excess glucose. Although in most microbial ecosystems provision of additional substrates leads to an increase in biomass, glucose had only a small effect on the numbers of S. mutans. Mechanical dislodging forces could be limiting the accumulation of dental plaque. EPS synthesis from dietary carbohydrates seems to enable the population to withstand mechanical dislodging at least partially by providing a matrix wherein cells are entrapped or to which the cells are firmly attached.

Nodule initiation elicited by noninfective mutants of Rhizobium phaseoli.

Rhizobium phaseoli CE106, CE110, and CE115, originally derived by transposon mutagenesis (Noel et al., J. Bacteriol. 158:149-155, 1984), induced the formation of uninfected root nodule-like swellings on bean (Phaseolus vulgaris). Bacteria densely colonized the root surface, and root hair curling and initiation of root cortical-cell divisions occurred normally in mutant-inoculated seedlings, although no infection threads formed. The nodules were ineffective, lacked leghemoglobin, and were anatomically distinct from normal nodules. Ultrastructural specialization for ureide synthesis, characteristic of legumes that form determinate nodules, was absent. Colony morphology of the mutant strains on agar plates was less mucoid than that of the wild type, and under some cultural conditions, the mutants did not react with Cellufluor, a fluorescent stain for beta-linked polysaccharide. These observations suggest that the genetic lesions in these mutants may be related to extracellular polysaccharide synthesis.

Stimulation of extracellular polysaccharide synthesis in oat protoplasts by the host-specific phytotoxin victorin

The host-specific phytotoxin victorin (HV-toxin) stimulates mesophyll protoplasts of susceptible but not of resistant oat (Avena sativa L.) to produce an amorphous, ethanol-insoluble extracellular material which stains with Calcofluor white and aniline blue. Over a 24-h period incorporation of [(14)C]glucose into ethanol-insoluble products is maximally stimulated by 60 pg victorin/ml, whereas at 6 ng/ml initial rates of incorporation are higher but the protoplasts collapse. The extracellular material produced in response to victorin is solubilized by cold 4.4 N NaOH and by commercial laminarinase and pectinase. Incorporation of [(14)C]glucose into cellulose (material resistant to Updegraff's acetic-nitric acid reagent) is stimulated as much as incorporation into other wall polysaccharides, but cellulose constitutes less than 15% of the total victorin-stimulated incorporation. Synthesis of ethanol-insoluble material that can be digested by pronase, i.e. protein, is inhibited by victorin above 60 pg victorin/ml. Formation of extracellular polysaccharide is stimulated at concentrations of victorin which cause almost complete inhibition of protein synthesis, indicating that de-novo protein synthesis is not involved. Preincubation of protoplasts with inhibitors of RNA or protein synthesis prevents both extracellular polysaccharide synthesis and cell death in response to victorin. Although previous studies have indicated a link between calcium and the action of victorin, several compounds which interact with calcium do not influence this response to victorin.

INFLUENCE OF GROWTH STATUS AND NUTRIENTS ON EXTRACELLULAR POLYSACCHARIDE SYNTHESIS BY THE SOIL ALGACHLAMYDOMONAS MEXICANA(CHLOROPHYCEAE)1

ABSTRACTIncreased levels of nitrogen in liquid growth medium bring about increased growth and a delay in extracellular polysaccharide production byChlamydomonas mexicanaLewin on a per‐cell basis. Addition of nitrogen to stationary phase cultures causes renewed growth and a temporary lag in polysaccharide synthesis until growth again ceases. Removal of nitrogen terminates growth, causing an immediate increase in polysaccharide synthesis. Phosphate‐starved cells show a response similar to nitrogen‐starved cells, indicating that the beginning of stationary phase and not nitrogen depletion causes the stimulation in extracellular polysaccharide synthesis. As similar results are assumed to occur on soil, the significance of this response is discussed.

Scanning electron microscopic studies of the extracellular polysaccharides (EP) synthesized in colonies of Streptococcus mutans: development of EP and the effect of dextranase on them.

Microbiology and ImmunologyVolume 26, Issue 7 p. 623-628 ArticleFree Access Scanning Electron Microscopic Studies of the Extracellular Polysaccharides (EP) Synthesized in Colonies of Streptococcus mutans: Development of EP and the Effect of Dextranase on Them Fusao OTA, Fusao OTA Department of Oral Microbiology, School of Dentistry, The University of Tokushima, Tokushima, Tokushima 770Search for more papers by this authorKomei FUKUI, Komei FUKUISearch for more papers by this author Fusao OTA, Fusao OTA Department of Oral Microbiology, School of Dentistry, The University of Tokushima, Tokushima, Tokushima 770Search for more papers by this authorKomei FUKUI, Komei FUKUISearch for more papers by this author First published: July 1982 https://doi.org/10.1111/mim.1982.26.7.623Citations: 1AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat REFERENCES 1Guggenheim, B., and Schroeder, H.E. 1967. Biochemical and morphological aspects of extracellular polysaccharides produced by cariogenic streptococci. Hely. Odont. Acta 11: 131– 152. 2Guggenheim, B. 1970. Enzymatic hydrolysis and structure of water insoluble glucans produced by glucosyltransferases from a strain of Streptococcus mutans. Hely. Odont. Acta (Suppl. V) 14: 89– 108. 3Hamada, S., Mizuno, J., Murayama, Y., Ooshima, T., Masuda, N., and Sobue, S. 1975. Effect of dextranase on the extracellular polysaccharide synthesis of Streptococcus mutans: Chemical and scanning electron microscopy studies. Infect. Immun. 12: 1415– 1425. 4Hamada, S., and Slade, H.D. 1980. Biology, immunology and cariogenicity of Streptococcus mutans. Microbiol. Rev. 44: 331– 384. 5Johnson, M.C., Bozzola, J.J., and Schechmeister, I.L. 1974. Morphological study of Streptococcus mutans and two extracellular polysaccharide mutants. J. Bacteriol. 118: 304– 311. 6Newbrun, E. 1972. Extracellular polysaccharides synthesized by glucosyltransferases of oral streptococci. Caries Res. 6: 132– 147. 7Ota, F., Fukui, K., Saito, R., Akiyama, Y., Satomi, Y., Yasuoka, M., and Kashiyama, T. 1981. Studies on oral miroorganisms. VI. Morphological studies on oral streptococci by scanning electron microscopy. Shikoku Acta Medica 37: 42– 60 (in Japanese with English summary). 8Whittaker, D.K., and Drucker, D.B. 1970. Scanning electron microscopy of intact colonies of microorganisms. J. Bacteriol. 104: 902– 909. Citing Literature Volume26, Issue7July 1982Pages 623-628 ReferencesRelatedInformation

The Effect of Some Divalent Cations on Extracellular Polysaccharide Synthesis in Streptococcus salivarius

The amount of extracellular insoluble polysaccharide produced by Streptococcus salivarius can be effected by some divalent cations. Calcium at concentrations of 1 X 10(-3) and 10(-4) M caused a reduction in polysaccharide synthesis. Magnesium at 1 X 10(-3) M inhibited extracellular polysaccharide production but at 1 X 10(-4) M had little effect. Manganese was without effect on polysaccharide synthesis. Zinc at 1 X 10(-3) and 1 X 10(-4) M caused a substantial increase in extracellular polysaccharide synthesis.

Regulation of Synthesis and Secretion of Fucose-containing Polysaccharides in Cultured Sycamore Cells

Regulation of the synthesis and secretion of sycamore extracellular polysaccharides (SEPS) was studied in cultured cells of Acer pseudoplatanus L. cv. Pope by monitoring the incorporation of L-[3H]fucose, a specific marker for the polysaccharide, into cell wall, soluble intracellular polysaccharide and secreted fractions. Actively growing cultures of sycamore cells produce SEPS, and it reaches a concentration in the incubation medium of up to 0.7 mg ml-� after 25 days of growth. Addition of SEPS at 10 mg ml-� to cells during the phase of active growth causes a marked and rapid inhibition of secretion of the polysaccharide into which [3H]fucose is incorporated without markedly affecting uptake of the label. Added SEPS also inhibits the incorporation of [3H]fucose into the homogenate fraction although this inhibition is less marked and requires higher concentrations of added SEPS. This inhibitory effect of SEPS can be mimicked by other charged polymers, for example polygalacturonic acid, polylysine and polyglycine, while uncharged polymers like polyethylene glycol and dextran are without effect. Furthermore, the incorporation of [3H]fucose into secreted polysaccharides of isolated protoplasts is relatively unaffected by added SEPS. We propose that SEPS and other charged polymers interact with the cell wall causing it to become impermeable to synthesized SEPS, which then accumulates between the plasmalemma and the cell wall and eventually inhibits polysaccharide synthesis.

Extracellular glucans synthesized by strains of two types of Streptococcus mutans in vitro

33 strains of Strep. mutans were used to synthesize extracellular polysaccharides in vitro. It was established by biochemical methods that 10 of these strains resembled Strep. mutans type c, and 23 type d. The extracellular polysaccharides were identified as glucans by acid hydrolysis and enzymic determination of the split products. The type d strains synthesized significantly higher amounts of extracellular polysaccharides per gram bacterial mass than the type c strains. The ratio of soluble to insoluble polysaccharides was significantly higher with the type c strains. Repeated synthesis of extracellular polysaccharides by one strain of each type showed reproducible results. The differences with respect to amounts and types of extracellular polysaccharides might be due to the opposite action of streptococcal glucosyltransferase and glucanhydrolase.

Influence of Salivary Components and Extracellular Polysaccharide Synthesis from Sucrose on the Attachment of Streptococcus mutans 6715 to Hydroxyapatite Surfaces

The adsorption of (3)H-labeled Streptococcus mutans 6715 cells to disks of hydroxyapatite (HA) was studied. The number of streptococci that adsorbed was logarithmically related to the concentration of cells available up to at least 2 x 10(8) per ml; equilibrium occurred within 45 min. Assay reliability was verified by direct scanning electron microscopic counts. Untreated HA disks exposed to buffered saline (PBS)-suspended streptococci at a concentration of 1.1 x 10(8) per ml absorbed 3.2 x 10(6) cells per cm(2); approximately 3% of the surface area was, therefore, occupied by adsorbed organisms. The presence of adsorbed salivary components on HA reduced the number of attaching S. mutans cells by half. When S. mutans cells were suspended in saliva to mimic conditions existing in the mouth, the number of streptococci adsorbing to saliva-treated HA was reduced more than 30-fold compared to untreated HA. Approximately one-half of the streptococci adsorbed to untreated or to saliva-treated HA disks could be desorbed over a 4-h period with 0.067 M phosphate buffer. S. mutans cells exposed to sucrose to permit extracellular polysaccharide synthesis before or during adsorption attached in fewer numbers to both saliva-treated and untreated HA than PBS-treated organisms. When S. mutans cells adsorbed on untreated HA were exposed to sucrose, fewer organisms could be desorbed; thus, in situ polysaccharide synthesis promoted their more firm attachment to untreated HA. However, when saliva-suspended streptococci were adsorbed to saliva-treated HA surfaces, exposure to sucrose before or subsequent to adsorption did not promote more firm attachment. Evidently, the powerful adherence-inhibiting and desorptive effects of salivary components overshadowed any promoting effects attributable to glucan synthesis from sucrose. Similarly, no differences were noted in the desorption of S. mutans cells from human teeth after exposure to sucrose, glucose, or PBS relative to a strain of Streptococcus mitis (S. mitior). Thus, no evidence was obtained to support the hypothesis that glucan synthesis from sucrose was essential for, or promoted, the attachment of S. mutans cells to HA surfaces exposed to saliva or to the smooth surfaces of human teeth.

Effects of sulphate-limited growth in continuous culture on the electron-transport chain and energy conservation in Escherichia coli K12

Growth of Escherichia coli K12 in a chemostat was limited by sulphate concentrations lower than 300 muM. The synthesis of extracellular polysaccharide and a change in morphology accompanied sulphate-limited growth. Growth yields with respect to the amount of glycerol or oxygen consumed were sixfold and twofold lower respectively under these conditions than when growth was limited by glycerol. Sulphate-limited cells lacked the proton-translocating oxidoreduction segment of the electron-transport chain between NADH and the cytochromes, and particles prepared from these cells lacked the energy-dependent reduction of NAD+ by succinate, DL-alpha-glycerophosphate or D-lactate, suggesting the loss of site-I phosphorylation. Glycerol-limited cells contained cytochrome b556, b562 and o, ubiquinone and low concentrations of menaquinone. Sulphate limitation resulted in the additional synthesis of cytochromes d, a1, b558 and c550; the amount of ubiquinone was decreased and menaquinone was barely detectable. Non-haem iron and acid-labile sulphide concentrations were twofold lower in electron-transport particles prepared from sulphate-limited cells. Recovery of site-I phosphorylation could not be demonstrated after incubating sulphate-limited cells with or without glycerol, in either the absence or presence of added sulphate. The loss of site-I phosphorylation in sulphate-limited cells is discussed with reference to the accompanying alterations in cytochrome composition of such cells. Schemes are proposed for the functional organization of the respiratory chains of E. coli grown under conditions of glycerol or sulphate limitation.

Effect of dextranase on the extracellular polysaccharide synthesis of Streptococcus mutans; chemical and scanning electron microscopy studies.

A dextranase preparation (AD17) partially purified from a culture liquor of Spicaria violacea strain IFO 6120 significantly inhibited the formation of artifcial dental plaque on a steel wire or on an extracted tooth surface. Changes in the surface morphology of Streptococcus mutans cells due to AD17 action were studied using scanning electron microscopy. S. mutans cells grown in 5% sucrose-containing broth were coated with sticky amorphous capsule-like material, whereas cells grown in sucrose in the presence of AD17 or in glucose instead of sucrose did not synthesize such capsular material. AK17 degraded commercially available dextrans of molecular weight 7 X 1(04) and 2 X 10(6) to liberate glucose and various oligosaccharides, including isomaltose. On the other hand, AD17 hydrolyzed the extracellular polysaccharides (mainly glucan in nature) of some strains of S. mutans to a limited degree. Only 15 to 36% of the total polysaccharides were hydrolyzed by AD1M with little release of isomaltose. Prolonged incubation of the polysaccharides from S. mutans with AD17 did not release additional reducing sugars, which indicates that AD17 did not contain alpha-1,3-glucanase activity. These results suggest that glucosidic linkages which are susceptible to AD17 may play an important role in the adherence of S. mutans cells to smooth surfaces.