Protection of photosystem II against UV-A and UV-B radiation in the cyanobacterium Plectonema boryanum: the role of growth temperature and growth irradiance

Plectonema boryanum UTEX 485 cells were grown at 29 degrees C and 150 mumol m-2 s-1 photosynthetically active radiation (PAR) and exposed to PAR combined with ultraviolet-A radiation (UV-A) at 15 degrees C. This induced a time-dependent inhibition of photosystem II (PSII) photochemistry measured as a decrease of the chlorophyll a fluorescence ratio, Fv/Fm, to 50% after 2 h of UV-A treatment compared to nontreated control cells. Exposure of the same cells to PAR combined with UV-A + ultraviolet-B radiation (UV-B) caused only a 30% inhibition of PSII photochemistry relative to nontreated cells. In contrast, UV-A and UV-A + UV-B irradiation of cells cultured at 15 degrees C and 150 mumol m-2 s-1 had minimal effects on the Fv/Fm values. However, cells grown at 15 degrees C and lower PAR irradiance (6 mumol m-2 s-1) exhibited similar inhibition patterns of PSII photochemistry as control cells. The decreased sensitivity of PSII photochemistry of P. boryanum grown at 15 degrees C and 150 mumol m-2 s-1 to subsequent exposure to UV radiation relative to either control cells or cells grown at low temperature but low irradiance was correlated with the following: (1) a reduced efficiency of energy transfer to PSII reaction centers; (2) higher levels of a carotenoid tentatively identified as myxoxanthophyll; (3) the accumulation of scytonemin and mycosporine amino acids; and (4) the accumulation of ATP-dependent caseinolytic proteases. Thus, acclimation of P. boryanum at low temperature and moderate irradiance appears to confer significant resistance to UV-induced photoinhibition of PSII. The role of excitation pressure in the induction of this resistance to UV radiation is discussed.     

Observation of CO(2) in Fourier transform infrared spectral measurements of living Acholeplasma laidlawii cells

In monitoring the time course of conformational disorder by Fourier transform infrared spectroscopy for intact Acholeplasma laidlawii cells grown at 37 degrees C on binary fatty acid mixtures containing oleic acid and for cells grown on pure palmitic acid, an absorption band at 2343 cm(-1) was observed. The band intensity was found to increase with time. This band was not observed in the spectra for isolated membranes. It is suggested that the 2343 cm(-1) band is due to CO(2) dissolved in water, most likely produced at the final point of fermentation of amino acid by this microorganism.     

Temperature-dependent shift from labile to recalcitrant carbon sources of arctic heterotrophs

Soils of high latitudes store approximately one-third of the global soil carbon pool. Decomposition of soil organic matter (SOM) is expected to increase in response to global warming, which is most pronounced in northern latitudes. It is, however, unclear if microorganisms are able to utilize more stable, recalcitrant C pools, when labile soil carbon pools will be depleted due to increasing temperatures. Here we report on an incubation experiment with intact soil cores of a frost-boil tundra ecosystem at three different temperatures (2 degrees C, 12 degrees C and 24 degrees C). In order to assess which fractions of the SOM are available for decomposition at various temperatures, we analyzed the isotopic signature of respired CO2 and of different SOM fractions. The delta13C values of CO2 respired were negatively correlated with temperature, indicating the utilization of SOM fractions that were depleted in 13C at higher temperatures. Chemical fractionation of SOM showed that the water-soluble fraction (presumably the most easily available substrates for microbial respiration) was most enriched in 13C, while the acid-insoluble pool (recalcitrant substrates) was most depleted in 13C. Our results therefore suggest that, at higher temperatures, recalcitrant compounds are preferentially respired by arctic microbes. When the isotopic signatures of respired CO2 of soils which had been incubated at 24 degrees C were measured at 12 degrees C, the delta13C values shifted to values found in soils incubated at 12 degrees C, indicating the reversible use of more easily available substrates. Analysis of phospholipid fatty acid profiles showed significant differences in microbial community structure at various incubation temperatures indicating that microorganisms with preference for more recalcitrant compounds establish as temperatures increase. In summary our results demonstrate that a large portion of tundra SOM is potentially mineralizable.     

MEASUREMENT OF DNA CROSSLINKS BY S1 NUCLEASE: INDUCTION AND REPAIR IN PSORALEN-PLUS-360 nm LIGHT TREATED ESCHERICHIA COLI

Abstract—DNA crosslinks in Escherichia coli cells. exposed to 4.5',8-trimethylpsoralen plus 360 nm light, were measured using a rapid and sensitive new approach. The assay is based on the specificity of S₁ nuclease from Aspergillus oryzae to single-stranded DNA. Bacterial cells were lysed and the DNA denatured by alkali. Following acid neutralization. crosslinked DNA undergoes spontaneous renaturation and is rendered S₁-nuclease resistant and therefore acid-precipitable. The single-stranded fraction after denaturation by alkali decreases with increasing near UV light exposure in the presence of TMP following first order kinetics. The kinetics were faster when exposure was at 4°C rather than at 20°C. This suggests that excision of crosslinks occurs during exposure at the higher temperature. Indeed. since the rate of DNA crosslinking in a uvr B mutant which is excision-deficient was higher than in wild type bacteria at 4°C, some excision must have occurred even in the cold. DNA from excision-proficient cells incubated at 37°C following exposure to TMP-plus-near UV at 4° showed a greater single stranded fraction than that from non-incubated cells. This indicates repair of DNA crosslinks. which proceeded with a half-time of 8 min at 37°C and was unaffected by substitution of thymine in DNA by 5-bromouracil.     

POSTREPLICATION REPAIR IN uvrA AND uvrB STRAINS OF ESCHERICHIA COLI K-12 IS INHIBITED BY RICH GROWTH MEDIUM

Abstract Escherichia coli K-12 uvrA or uvrB strains grown to logarithmic phase in minimal medium showed higher survival after ultraviolet (UV) irradiation (254 nm) if plated on minimal medium (MM) instead of rich medium. This'minimal medium recovery'(MMR) was largely blocked by additional recA56 (92% inhibition) or lexA101 (77%) mutations, was partially blocked by additional recB21 (54%), uvrD3 (31%) or recF143 (22%) mutations, but additional polA1 or polA5 mutations had no effect on MMR. When incubated in MM after UV irradiation, the uvrB5 and uvrB5 uvrD3 strains showed essentially complete repair of DNA daughter-strand gaps (DSG) produced after UV radiation fluences up to ∼ 6 J/m² and ∼1 J/m², respectively, and then they accumulated unrepaired DSG as a linear function of UV radiation fluence. However, when they were incubated in rich growth medium after UV irradiation, they did not show the complete repair of DSG and unrepaired DSG accumulated as a linear function of UV radiation fluence. The fluence-dependent correlation observed for the uvrB and uvrB uvrD cells between UV radiation-induced killing and the accumulation of unrepaired DSG, indicates that the molecular basis of MMR is the partial inhibition of postreplication repair by rich growth medium. Rich growth medium can be just MM plus Casamino Acids or the 13 pure amino acids therein in order to have an adverse effect on survival, regardless of whether the cells were grown in rich medium or not before UV irradiation.     

A medium for the presumptive detection of Enterobacter sakazakii in infant formula: interlaboratory study

A standard method for the detection of Enterobacteriaceae was modified for the presumptive detection of Enterobacter sakazakii, and the modified method was validated in an interlaboratory trial with 16 laboratories from 8 European countries. The modification included a differential-elective medium for the isolation of E. sakazakii, consisting of nutrient agar (NA) supplemented with 4-methyl-umbelliferyl alpha-D-glucoside (alpha-MUG). A 25 g sample was added to 225 mL buffered peptone water. After incubation at 35 degrees or 37 degrees C for 16 or 20 h, 10 mL nonselective enrichment was transferred into 90 mL selective enrichment. The selective enrichment was streaked on violet-red bile glucose agar (VRBGA) and incubated at 37 degrees C for 24 h. It was streaked in parallel on NA plates supplemented with alpha-MUG at 50 mg/L and incubated at 25 degrees C for 16 h, and afterwards for an additional 24 h at room temperature in the dark. E. sakazakii appeared as vivid yellow colonies under normal light and showed blue/violet fluorescence under UV light on NA + alpha-MUG plates. Validation samples represented powdered infant formula without E. sakazakii (blanks) and with low (1-10 colony-forming units [CFU]/25 g) and medium (1-10 CFU/g) contamination levels. All samples contained Pseudomonas aeruginosa and Lactobacillus spp. as background flora. The specificity for blank samples was 100%. The sensitivity of the low contamination level was similar for VRBGA and NA + alpha-MUG, i.e., 66.7% (66.7% accordance, 53.9% concordance). For the medium level the sensitivities were 96.7% (93.3% accordance, 93.5% concordance) for VRBGA and 98.3% (96.9% accordance, 96.9% concordance) for NA + alpha-MUG.     

Thermotropic Liquid‐Crystalline Polymer Derived from Natural Cinnamoyl Biomonomers

Summary: The compound 4‐hydroxycinnamic acid (4HCA), a natural biomonomer, is polymerized by melt polycondensation to yield a liquid‐crystalline biopolymer (P4HCA) with UV reactivity. L929 cells were successfully incubated on P4HCA films at 37 °C.

Structure of poly(4‐hydroxycinnamic acid) (P4HCA) and its crossed‐polarizing optical micrograph in the nematic state. Inset image: optical micrograph of L929 mouse fibroblasts adhered on P4HCA film after 24 h incubation at 37 °C.     

THE EFFECT OF ULTRAVIOLET RADIATION ON WHEAT ROOT VESICLES ENRICHED IN PLASMA MEMBRANE

Abstract— The irradiation of plant cells with UV radiation (254nm) causes various solutes to leak from the cells. Vesicles enriched in plasma membranes were prepared from wheat roots. These were used to determine whether UV radiation alters membrane function by direct action on the membranes and to distinguish between the chemical effects produced by high and low fluences of UV. The plasma membrane-associated K⁺-stimulated ATPase was very sensitive to UV radiation (100% inhibition with 1.35kJ/m²). ATPase activity measured in the absence of K⁺ and K⁺-stimulated ATPase activity measured in the presence of diethylstilbestrol were much less sensitive. Lipid breakdown, as measured by malondialdehyde production, occurred only at UV fluences greater than 1.8 kJ/m².     

REC A +-DEPENDENT SYNERGISM BETWEEN 365 NM AND IONIZING RADIATION IN LOG-PHASE ESCHERICHIA COLI: A MODEL FOR OXYGEN-DEPENDENT NEAR-UV INACTIVATION BY DISRUPTION OF DNA REPAIR

Abstract —The oxygen dependence of 365 nm inactivation of colony-forming ability of Escherichia coli has been investigated in two series of DNA repair-deficient K12 mutants grown to mid-exponential phase. All strains except a uvr A rec A double mutant are more sensitive to inactivation under O₂ and show a lower threshold dose. The inactivation of photoreactivating enzyme in a crude cell extract and DNA repair disruption are both reduced when irradiation is carried out under nitrogen. The rec A gene-dependent synergism between 365 nm and ionising radiation is reversible if cells are incubated in full growth medium before ionising radiation treatment. In a wildtype strain, incubation for 2.5 h in full growth medium after 10⁶ J m^-2 365 nm radiation changes a sensitised response to a protection from ionising radiation. Protection is not seen at 1.5 times 10⁶ J m^-2. A tentative model for near UV lethality in logarithmic phase cells is suggested which proposes two classes of lesions. One requires oxygen for it's induction, is rapidly fixed as a lethal event as a result of repair disruption, and is primarily responsible for cell death after aerobic 365 nm irradiation. The other lesion, possibly pyrimidine dimers, may lead to cell death under anaerobic conditions.     

MEMBRANE DAMAGE AND RECOVERY ASSOCIATED WITH GROWTH DELAY INDUCED BY NEAR-UV RADIATION IN Escherichia coliK–12

Abstract— The growth delay induced by near-UV radiation has been largely attributed to injured tRNA's and to the stringent response. We report an associated membrane perturbation whose recovery determines substantial modifications in the behavior of log phase Escherichia coli K–12 exposed to sublethal doses of near-UV radiation (366 nm). When incubated at 37°C in plain nutrient broth, cells suffered a growth delay of about 100 min with parallel inhibition of several membrane functions. Conversely, when grown in conditions known to influence membrane activities, these were slightly inhibited and the growth delay lasted about 50 min. All the above conditions triggered the stringent response, characterized by an equivalent post-irradiation burst of intracellular guanosine 5'3' tetra and pentaphosphate and by a similar decay rate of the nucleotides accumulated at time 0 of the growth lag. According to our data the polyphosphates' half decay time in irradiated cells remains practically constant and close to 15 min. But, while cells from unsupplemented broth at 37°C resumed normal growth in around 100 min those with recovered membranes were rescued from growth inhibition in about one half of that time.     

RESPONSES OF THE PLANARIAN Dugesia dorotocephala TO ULTRAVIOLET RADIATION OR PHOTOSENSITIZED TREATMENTS

Abstract— The survival of the planarian Dugesia dorotocephala was measured following treatment with germicidal ultraviolet (UV) radiation, with the DNA photosensitizer 8-methoxypsoralen (8-MOP) plus near UV radiation, or with the cytoplasm photosensitizer erythrosin plus visible radiation. The typical morphological response of an irradiated animal was lysis, with the head being the most sensitive part. All the survival curves had substantial shoulders. Treatments whose primary target was likely to be DNA (UV irradiation or 8-MOP plus near UV irradiation) resulted in lysis of part of the planarian population which commenced 24 h or more after treatment and continued over several days. The treatment whose primary target was likely to be the membranes of the planarian (erythrosin plus visible irradiation) resulted in lysis mostly during the first few hours after treatment. Thus an easily discerned endpoint, lysis, can be used for D. dorotocephala to evaluate photosensitizing compounds, where the kinetics of lysis may differentiate among compounds whose modes of action are different.     

Determination of phosphorylation sites in lipooligosaccharides from Pseudoalteromonas haloplanktis TAC 125 grown at 15 degrees C and 25 degrees C by nano-electrospray ionization quadrupole time-of-flight tandem mass spectrometry

Lipooligosaccharides (LOSs) are macromolecules present on the external cellular membrane of Gram-negative bacteria, structurally made of two distinct regions, lipid A and Core. By varying their growth temperature, bacteria such as psychrophiles change the phosphorylation distribution of the LOSs produced. The level of phosphorylation and the phosphate group positions in LOSs produced by the extremophile psychrophilic bacterium Pseudoalteromonas haloplanktis TAC 125, grown at 15 degrees C and 25 degrees C, were investigated by nano-electrospray ionization quadrupole time-of-flight mass spectrometry (nanoESI-QTOF-MS) and tandem mass spectrometry (MS/MS). The samples, obtained by phenol/chloroform/petroleum ether (PCP) extraction of dried cells, were treated with hydrazine at 37 degrees C in order to reduce the heterogeneity by removal of the ester-linked fatty acid moieties. The molecular ion distributions in these LOS fractions were investigated in negative ion mode. Based on these data it was postulated that the sample grown at 25 degrees C contained four phosphate groups while that at 15 degrees C contained three. In order to determine phosphorylation sites in sugar chains, the samples were submitted to low collision energy MS/MS for sequencing. In the sample with three phosphates, one was found to be linked to the tetrasaccharide Core region, more precisely to position C-4 of the Kdo unit. The two remaining phosphate groups were both linked to the 2-acylamide-2-deoxy-D-glucopyranose of the lipid A moiety, and two possible distributions could be postulated on the basis of the fragmentation pattern obtained; in the first case both phosphate groups are linked as a pyrophosphate moiety to position C-1 of the proximal glucosamine (reducing residue), while in the second case one phosphate is linked to position C-1 of the proximal glucosamine and the other to position C-4' of the distal glucosamine (non-reducing residue). This distribution was also found in the lipid A moiety of the tetraphosphorylated sample grown at 25 degrees C, which bears two phosphate groups on the Core region, one on position C-4 of the Kdo and the other on position C-7 or C-8 of the same residue. The phosphate locations were derived from the intra-ring cleavage ions of sugar moieties in the LOSs obtained by an optimized CID procedure using negative ion QTOF-MS/MS.     

牡励中脂肪酸在储藏过程中的稳定性

用超临界流体萃取及ＧＣ－ＭＳ分析了新冷冻干燥及保存１５ｄ,３０ｄ,４５ｄ,６０ｄ,７５ｄ,９０ｄ后的鲜牡蛎粉中的２３种脂肪酸组分的质量分数。发现在存放过程中牡蛎脂肪酸的稳定性与其不饱和度有关;不饱和度越高,脂肪酸越易被氧化,其中多不饱和记酸的氧化是逐渐进行的,没有特定的稳定期。     

Non-coherent visible and infrared radiation increase survival to UV (254 nm) in Escherichia coli K12

Interactions between visible or infrared (IR) and ultraviolet (UV, 254 nm) radiation have been studied in E. coli. Pre-illumination with non-coherent monochromatic 446, 466, 570 and 685 nm radiation, as well as with polychromatic red and IR radiation at room temperature, leads to increased cell survival after a subsequent irradiation with UV light. In the thermic range of the spectrum (red and IR), IR but not red light pre-treatment is able to increase cell survival to a subsequent lethal heat (51 degrees C) challenge, suggesting that increased UV survival may be due to IR-induced heat-shock response. On the other hand, visible-light-induced resistance may be due to a different mechanism, possibly involved with unknown bacterial light receptors.     

5种贝类脂肪含量及脂肪酸组成研究

 用氯仿 甲醇法测定了广州海鲜市场上棕带仙女蛤、波纹巴非蛤、文蛤、栉孔扇贝和园华扇贝等 5种贝类的脂肪含量 ,并用GC MS法测定了它们的脂肪酸组成。 5种贝类鉴定出的脂肪酸都在 99% (质量分数 )以上。它们的脂肪含量都大于 1% (质量分数 ) ,园华扇贝的脂肪含量最高。它们的ω 3多不饱和脂肪酸与ω 6多不饱和脂肪酸含量的比值基本上都大于 2。两种扇贝的廿碳五烯酸 (EPA)和廿二碳六烯酸 (DHA)含量都比较高。分析结果表明 ,园华扇贝不仅脂肪含量高 ,而且EPA与DHA的含量也比较高 ,是EPA和DHA理想的提取原料     

Structural heterogeneity and environmentally regulated remodeling of <Emphasis Type="Italic">Francisella tularensis</Emphasis> subspecies <Emphasis Type="Italic">novicida</Emphasis> lipid a characterized by tandem mass spectrometry

The structural characterization of environmentally-regulated lipid A derived from Francisella tularensis subspecies novicida (Fn) U112 is described using negative electrospray ionization with a linear ion trap Fourier transform ion cyclotron resonance (IT-FT-ICR) hybrid mass spectrometer. The results indicate that a unique profile of lipid A molecular structures are synthesized in response to Fn growth at 25 degrees C versus 37 degrees C. Molecular species were found to be tetra-acylated, sharing a conserved glucosamine disaccharide backbone, a galactosamine-1-phosphate linked to the reducing glucosamine, and multiple O- and N-linked fatty acyl groups. Deprotonated molecules were interrogated by MS(n) scanning techniques at both high and nominal mass resolution and were found to be complex heterogeneous mixtures where structures differed based on the positions and identities of the O- and N-linked fatty acyl substituents. For the dominant ion series, which consisted of five peaks, 30 unique lipid A structures were identified. Estimates for the relative abundance of each structure were derived from MS relative abundance ratios and fragment ion ratios from comparable dissociation pathways from MS(2) through MS(4) experiments. The results suggest a remodeling pathway in which the amide linked fatty acid of the reducing glucosamine favors a 3-hydroxyhexadecanoic acid substituent for growth conditions at 25 degrees C versus a 3-hydroxyoctadecanoic acid substituent for growth conditions at 37 degrees C.     

NEAR ULTRAVIOLET AND POSTIRRADIATION DNA DEGRADATION: EFFECTS ON THE INDUCIBLE INHIBITOR OF IONIZING RADIATION-INDUCED DNA DEGRADATION

Abstract— Possible effects of near ultraviolet radiation (near UV) on DNA degradation were examined. Postirradiation DNA degradation induced by ionizing radiation in strain B_s-l ( uur-, lex- ) is shown to be inhibited by carbon monoxide (CO) and potassium cyanide (KCN) if the cells are grown on glycerol. Presumably the blockage of respiration by these agents lowers the amount of ATP in the cell. 50 kJ/m² near UV did not simulate the action of CO and KCN, indicating that at this Ruence the supply of ATP remains adequate for postirradiation DNA degradation. Near UV did not, itself, produce DNA degradation. In a strain (B/r) in which an inhibitor of postirradiation DNA degradation can be induced by both UV and ionizing radiation, near UV affects the inhibitor formation, whether administered before or after induction.     

Thermally changing lattice distance of lamella in the hydrated solid of octadecyltrimethylammonium chloride

A temperature scanning small-angle X-ray scattering measurement was carried out for the hydrated solids of octadecyltrimethylammonium chloride (OTAC). A gradual change of the lattice spacing of lamella-like structure from 40 nm at 5 degrees C to 20 nm at 18 degrees C was observed in the melting process of the hydrated solid that was incubated at 4 degrees C for a period of 24 h in the aqueous solution, while little change of the lattice spacing of about 20 nm was observed in the same process of the hydrated solid that was incubated at 4 degrees C for a period about 10 min. This indicates structural changes of the hydrated solid during the incubation at 4 degrees C and in the melting process. Corresponding to the nanostructure changes, broad endothermic peaks were observed at temperatures from 13 to 22 degrees C for the former hydrated solid and at temperatures from 15 to 21 degrees C for the latter hydrated solid in difference scanning calorimetry measurements. The structure change at temperatures below 13 degrees C is considered to be athermal from the fact that no endothermic peak is observed there. Large dielectric dispersions at frequencies at about 10 kHz were observed for the suspensions of hydrated solids but not for the solutions of dissolved solids. It was found that the electric conductance of the hydrated solid suspensions was much lower than that of the solutions of dissolved solids. The observed electric properties indicate that an amount of the free chloride ion is very small and that the chloride ions binding to the ammonium groups are movable in the hydrated solids by responding to an applied electric field. The electric conductance of suspension of the hydrated solid being incubated at 4 degrees C for 10 min was 4 times as large as that of a suspension of the hydrated solid being incubated at the same temperature for 24 h. This indicates that the structural change of the OTAC hydrated solid at 4 degrees C is related to the chloride ion binding to the hydrated solid. The experimental results described above suggest that the lamella in the hydrated solid of OTAC is undulated and that the wavelength of undulation increases with the incubation at a temperature much lower than the melting temperature.     

Effect of beta-lactoglobulin hydrolysis with thermolysin under denaturing temperatures on the release of bioactive peptides

In this study, bovine beta-lactoglobulin A (beta-Lg A) was hydrolysed with thermolysin under non-denaturing and heat-denaturing conditions. The peptides released during hydrolysis were identified by HPLC-MS/MS. A total of 25 peptides were identified in the hydrolysate obtained at 37 degrees C for 5 min. Some of these peptides survived to further proteolysis even at higher incubation temperatures. Furthermore, novel cleavage sites localised in the most buried zones of beta-Lg and available for thermolysin were recognised when the incubation temperature increased in the range between 60 and 80 degrees C. Three new peptides, LDA, LKPTPEGD, and LQKW, appeared after 30 min hydrolysis at these incubation temperatures, but they were not identified in the 30-min hydrolysates obtained at 37 and 50 degrees C. Of special interest was the peptide LQKW, corresponding to the fragment f(58-61) that had been previously described as a potent angiotensin-converting enzyme-inhibitor (IC50 value of 34.7 microM).     

Surface Aggregation of Candida albicans on Glass in the Absence and Presence of Adhering Streptococcus gordonii in a Parallel-Plate Flow Chamber: A Surface Thermodynamical Analysis Based on Acid-Base Interactions

Adhesive interactions between yeasts and bacteria are important in the maintenance of infectious mixed biofilms on natural and biomaterial surfaces in the human body. In this study, the extended DLVO (Derjaguin-Landau-Verwey-Overbeek) approach has been applied to explain adhesive interactions between C. albicans ATCC 10261 and S. gordonii NCTC 7869 adhering on glass. Contact angles with different liquids and the zeta potentials of both the yeasts and bacteria were determined and their adhesive interactions were measured in a parallel-plate flow chamber.Streptococci were first allowed to adhere to the bottom glass plate of the flow chamber to different seeding densities, and subsequently deposition of yeasts was monitored with an image analysis system, yielding the degree of initial surface aggregation of the adhering yeasts and their spatial arrangement in a stationary end point. Irrespective of growth temperature, the yeast cells appeared uncharged in TNMC buffer, but yeasts grown at 37 degrees C were intrinsically more hydrophilic and had an increased electron-donating character than cells grown at 30 degrees C. All yeasts showed surface aggregation due to attractive Lifshitz-van der Waals forces. In addition, acid-base interactions between yeasts, yeasts and the glass substratum, and yeasts and the streptococci were attractive for yeasts grown at 30 degrees C, but yeasts grown at 37 degrees C only had favorable acid-base interactions with the bacteria, explaining the positive relationship between the surface coverage of the glass by streptococci and the surface aggregation of the yeasts. Copyright 1999 Academic Press.