Non-O157:H7 Shiga toxin (verocytotoxin)-producing Escherichia coli strains: epidemiological significance and microbiological diagnosis

Shiga toxin (Stx)-producing Escherichia coli (STEC) are important causes of diarrhoea and the haemolytic uremic syndrome (HUS). The most common STEC serotype implicated worldwide is E. coli O157:H7 that is diagnosed using procedures based on its typical phenotypic feature, the lack of sorbitol fermentation. In addition to E. coli O157:H7, a variety of non-O157:H7 STEC strains that usually ferment sorbitol and are thus missed by using the diagnostic protocol for E.coli O157:H7 have been isolated from patients. Among these sorbitol-fermenting (SF) non-O157:H7 STEC, SF E. coli O157:H⁻ and non-O157 STEC strains of serogroups O26, O103, O111 and O145 have emerged as significant causes of HUS and diarrhoea in continental Europe and have been associated with human disease in other parts of the world. Microbiological diagnosis of non-O157:H7 STEC strains is difficult due to their serotype diversity and the absence of a simple biochemical property that distinguishes such strains from the physiological intestinal microflora. Screening for non-O157:H7 STEC and their isolation from stools is presently based on the detection of Stx production or stx genes that are common characteristics of such strains. Molecular subtyping of the most frequent non-O157 STEC demonstrated that strains of serogroups O26, O103 and O111 belong to their own clonal lineages and show unique virulence profiles. SF STEC O157:H⁻ strains that have been isolated mostly in Central Europe represent a new clone within E. coli O157 serogroup which has its own typical combination of virulence factors. This revised version was published online in November 2006 with corrections to the Cover Date.     

Modifications in erythrocyte membrane zeta potential by Plasmodium falciparum infection

The zeta potential (ZP) is an electrochemical property of cell surfaces that is determined by the net electrical charge of molecules exposed at the surface of cell membranes. Membrane proteins contribute to the total net electrical charge of cell surfaces and can alter ZP through variation in their copy number and changes in their intermolecular interactions. Plasmodium falciparum extensively remodels its host red blood cell (RBC) membrane by placing 'knob'-like structures at the cell surface. Using an electrophoretic mobility assay, we found that the mean ZP of human RBCs was -15.7 mV. In RBCs infected with P. falciparum trophozoites ('iRBCs'), the mean ZP was significantly lower (-14.6 mV, p<0.001). Removal of sialic acid from the cell surface by neuraminidase treatment significantly decreased the ZP of both RBCs (-6.06 mV) and iRBCs (-4.64 mV). Parasite-induced changes in ZP varied by P. falciparum clone and the presence of knobs on the iRBC surface. Variations in ZP values were accompanied by altered binding of iRBCs to human microvascular endothelial cells (MVECs). These data suggest that parasite-derived knob proteins contribute to the ZP of iRBCs, and that electrostatic and hydrophobic interactions between iRBC and MVEC membranes are involved in cytoadherence.     

Exotic plant communities shift water-use timing in a shrub-steppe ecosystem

Semiarid areas in the US have realized extensive and persistent exotic plant invasions. Exotics may succeed in arid regions by extracting soil water at different times or from different depths than native plants, but little data is available to test this hypothesis. Using estimates of root mass, gravimetric soil water, soil-water potential, and stable isotope ratios in soil and plant tissues, we determined water-use patterns of exotic and native plant species in exotic- and native-dominated communities in Washington State, USA. Exotic and native communities both extracted 12 ± 2 cm of water from the top 120 cm of soil during the growing season. Exotic communities, however, shifted the timing of water use by extracting surface (0–15 cm) soil water early in the growing season (i.e., April to May) before native plants were active, and by extracting deep (0–120 cm) soil water late in the growing season (i.e., June to July) after natives had undergone seasonal senescence. We found that δ ¹⁸O values of water in exotic annuals (e.g., −11.8 ± 0.4 ‰ for Bromus tectorum L.) were similar to δ ¹⁸O values of surface soil water (e.g., −13.3 ± 1.4 ‰ at −15 cm) suggesting that transpiration by these species explained early season, surface water use in exotic communities. We also found that δ ¹⁸O values of water in taprooted exotics (e.g., −17.4 ± 0.3 ‰ for Centaurea diffusa Lam.) were similar to δ ¹⁸O values of deep soil water (e.g., −18.4 ± 0.1 ‰ at −120 cm) suggesting that transpiration by these species explained late season, deep water use. The combination of early-season, shallow water-use by exotic winter-actives and late-season, deep water-use by taprooted perennials potentially explains how exotic communities resist establishment of native species that largely extracted soil water only in the middle of the growing season (i.e., May to June). Early season irrigation or the planting of natives with established root systems may allow native plant restoration.     

Quantifying the surface characteristics and flocculability of Ralstonia eutropha

The microbial surface and flocculability were qualitatively characterized through the combination of the surface thermodynamic and the extended DLVO approaches, with Ralstonia eutropha, a polyhydroxybutyrate-producing bacterium, as an example. The negativity of the ζ potential of R. eutropha decreased from the initial −19.5 to −11 mV in its cultivation with the consumption of glucose. The total interfacial free energy (ΔG _adh) was changed from −80 to 28.5 mJ m⁻² in its entire growth process. This suggests that the bacterial surface changed from hydrophobic into hydrophilic, resulting in an alteration of its surface characteristics and flocculability in its different growth phases. As a result, the stability ratio of suspensions increased with the increasing cultivation time, indicating that the cell particles became more repulsive with each other and led to a more stable suspension of R. eutropha in its cultivation. The obtained information in this work might be useful for better understanding the surface characteristics and the flocculability and even manipulating its flocculability in the microbial growth process.     

Effects of ambient temperature and of temperature acclimation on nitrogen excretion and differential catabolism of protein and nonprotein resources in the intertidal snails,Littorina saxatilis (Olivi) and L. obtusata (L.)

Nitrogenous excretion in two snails, Littorina saxatilis (high intertidal) and L. obtusata (low intertidal) was studied in relation to temperature acclimation (at 4° and 21°C), including total N excretion rates, the fraction of urea in N excretion, corresponding O:N ratios and the partitioning of deaminated protein between catabolic and anabolic processes at 4°, 11° and 21°C. Aggregate N excretion rates in both species showed no significant compensatory adjustments following acclimation. Total weight specific N excretion rates at 21°C were higher in standard 3 mg L. saxatilis (739 ng N mg⁻¹ h⁻¹) than standard 5 mg L. obtusata (257 ng N mg⁻¹ h⁻¹) for snails acclimated to 21°C. Comparisons of Q₁₀ values of total weight specific N excretion to Q₁₀ values for weight specific oxygen consumption ({xxV}O₂) between 4° to 11 °C and 11° to 21°C indicated that, while total rates of catabolic metabolism ({xxV}O₂) and protein deamination in L. obtusata were essentially parallel, the relationship between N excretion and {xxV}O₂ in L. saxatilis revealed the partitioning of a larger share of deaminated protein carbon into anabolism at 4° and 21°C than at 11°C. Urea N accounted for a larger share of aggregate N excreted in L. saxatilis than in L. obtusata, but in both species urea N is a greater proportion of total N excreted when acclimated at 4°C (urea N: ammonia N ratio range: 1 to 2.15) than in snails acclimated to 21°C (urea N: ammonia N ratio range: 0.46 to 1.39). Molar O:N ratios indicate that the proportion of metabolism supported by protein catabolism is greater in L. saxatilis (O:N range: 2.5–8.4) than in L. obtusata (O:N range: 7.3–13.0). In both species, regardless of acclimation temperature, the O:N ratios are generally lowest (high protein catabolism) at 4°C and highest at 21°C.     

Astaxanthin production by <Emphasis Type="Italic">Phaffia rhodozyma</Emphasis> and <Emphasis Type="Italic">Haematococcus pluvialis</Emphasis>: a comparative study

Phaffia rhodozyma (now Xanthophyllomyces dendrorhous) and Haematococcus pluvialis are known as the major prominent microorganisms able to synthesize astaxanthin natural pigment. Important research efforts have been made to determine optimal conditions for astaxanthin synthesis. When the focus is on astaxanthin production, the maximal reported value of 9.2 mg/g cell is obtained within H. pluvialis grown on BAR medium, under continuous illumination (345 μmol photon m⁻² s⁻¹) and without aeration. Whereas fermentation by mutated R1 yeast grown on coconut milk produced 1,850 μg/g yeast. However, when looking at astaxanthin productivity, the picture is slightly different. The figures obtained with P. rhodozyma are rather similar to those of H. pluvialis. Maximal reported values are 170 μg/g yeast per day with a wild yeast strain and 370 μg/g yeast per day with mutated R1 yeast. In the case of H. pluvialis, maximal values ranged from 290 to 428 μg/g cell per day depending on the media (BG-11 or BAR), light intensity (177 μmol photon m⁻² s⁻¹), aeration, etc. The main aim of this work was to examine how astaxanthin synthesis, by P. rhodozyma and H. pluvialis, could be compared. The study is based on previous works by the authors where pigment productions have been reported.     

Physicochemical properties of Shiga toxigenic Escherichia coli

AIMS: To investigate the physicochemical surface properties, such as cellular surface charge, hydrophobicity and electron donor/acceptor potential of a selection of Shiga toxigenic Escherichia coli (STEC) isolates grown in broth and agar culture. METHODS AND RESULTS: Cellular surface charge was determined using zeta potential measurements. Hydrophobicity of the isolates was determined using bacterial adhesion to hydrocarbons assay, hydrophobic interaction chromatography and contact angle measurements. Microbial adhesion to solvents was used to determine the electron donor/acceptor characteristics. No differences of surface charge measurements were found between broth and agar grown cultures. Isolates belonging to serogroup O157 and serotypes O26:H11 and O111:H- were significantly (P < 0.05) less negatively charged than other STEC serotypes tested. All strains were hydrophilic with most methods and demonstrated a lower hydrophobicity in agar culture compared with broth culture. All strains demonstrated a strong microbial adhesion to chloroform indicating that STEC possess an electron donor and basic character. A relationship between serogroup O157 and other STEC serotypes was apparent using principal-component analysis (PCA). CONCLUSIONS: Combining the results for physicochemical properties using PCA differentiated between strains belonging to the O157 serogroup and other STEC/non-STEC strains. PCA found similar results for broth and agar grown cultures. SIGNIFICANCE AND IMPACT OF THE STUDY: Particular serotypes of STEC possess similar physicochemical properties which may play a role in their pathogenicity or potential attachment to various surfaces.     

Improvement of the multiple-stress tolerance of an ethanologenic <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis> strain by freeze-thaw treatment

An effective, simple, and convenient method to improve yeast’s multiple-stress tolerance, and ethanol production was developed. After an ethanologenic Saccharomyces cerevisiae strain SC521 was treated by nine cycles of freeze-thaw, a mutant FT9-11 strain with higher multiple-stress tolerance was isolated, whose viabilities under acetic acid, ethanol, freeze-thaw, H₂O₂, and heat-shock stresses were, respectively, 23-, 26-, 10- and 7-fold more than the parent strain at an initial value 2 × 10⁷ c.f.u. per ml. Ethanol production of FT9-11 was similar (91.5 g ethanol l⁻¹) to SC521 at 30°C with 200 g glucose l⁻¹, and was better than the parent strain at 37°C (72.5 g ethanol l⁻¹), with 300 (111 g ethanol l⁻¹) or with 400 (85 g ethanol l⁻¹) g glucose l⁻¹.     

Effects of temperature and carbon dioxide on green sturgeon blood–oxygen equilibria

There are three Northeast Pacific Rivers still supporting spawning populations of green sturgeon, Acipenser medirostris, but all have been modified hydrologically and thermally by dam construction. Age 1- to 3-year-old green sturgeon, progeny of artificially spawned, wild-caught Klamath River adults, were used to assess the effects of temperature and carbon dioxide on critical hematological parameters related to evolutionary adaptations of this species to its physical environment. In vitro measurement of the effect of temperature and carbon dioxide on blood–oxygen affinity and equilibrium curve shape yielded the following data for the respective temperature treatments (11, 15, 19, and 24°C): half-saturation values (P₅₀’s, kPa, a measure of affinity) 1.26, 1.44, 1.63, 1.69 for low-PCO₂ treatments and 2.08, 2.41, 2.74, 2.94 for high-PCO₂ treatments; Bohr factors −0.322, −0.327, −0.366, −0.536; and non-bicarbonate buffer values (slykes) −6, −3, −5, −8. Temperature sensitivities (ΔH, kJ mol O₂⁻¹) between these respective temperatures were −34.20, −15.24, −6.74 for low-PCO₂ treatments and −20.05, −27.00, and −11.55 for the high-PCO₂ treatments. These data suggest that juvenile green sturgeon may tolerate moderate environmental hypoxia, moderate aerobic activity, low to moderate hypercapnia, and moderate temperature changes in their environments.     

Optimization of Phosphatidylinositol-specific Phospholipase C Production Using Response Surface Methodology

Summary Response surface methodology was employed in optimizing the nutrient levels needed towards the optimal production of phosphatidylinositol-specific phospholipase C enzyme by Bacillus thuringiensis serovar. kurstaki. A 2³ factorial central composite experimental design was used. The multiple regression equation, relating the enzyme activity to the nutrient medium, was used to find the optimum values of glucose, peptone and dipotassium hydrogen phosphate. The optimum values of these variables for maximal enzyme production were found to be: glucose, 6.5 g l⁻¹; peptone, 5.38 g l⁻¹ and dipotassium hydrogen phosphate, 6.36 g l⁻¹ with the predicted enzyme activity of 0.96 U ml⁻¹.     

Controlling the oxidoreduction potential of the culture of <Emphasis Type="Italic">Clostridium acetobutylicum</Emphasis> leads to an earlier initiation of solventogenesis,thus increasing solvent productivity

Fermentative production of solvents (acetone, butanol, and ethanol) by Clostridium acetobutylicum is generally a biphasic process consisting of acidogenesis and solventogenesis. We report that the biphasic metabolism of C. acetobutylicum could be changed by oxidoreduction potential (ORP) regulation. When using air to control the ORP of the fermentation broth at −290 mV, an earlier initiation of solventogenesis was achieved. Solvent production reached 25.6 g l⁻¹ (2.8 g acetone l⁻¹, 16.8 g butanol l⁻¹, 6.0 g ethanol l⁻¹), a 35% increase compared with the ORP uncontrolled process. Metabolic flux analysis revealed that there was a general increase of the central carbon flux in the first 24 h of fermentation when ORP was controlled at −290 mV, compared with the control. Specifically, the solvent ratio (acetone:butanol:ethanol) was changed from 25:64:11 to 11:66:23 at ORP level of −290 mV, which might have resulted from the rigidity at acetyl-CoA node and the flexibility at acetoacetyl-CoA and butyryl-CoA nodes in response to ORP regulation.     

Short-and long-term effects of cadmium on transmembrane electric potential (E m) in maize roots

In this study, the effects of Cd on root growth, respiration, and transmembrane electric potential (E _m) of the outer cortical cells in maize roots treated with various Cd concentrations (from 1 μM to 1 mM) for several hours to one week were studied. The E _m values of root cells ranged between −120 and −140 mV and after addition of Cd they were depolarized immediately. The depolarization was concentration-dependent reaching the value of diffusion potential (E _D) when the Cd concentration exceeded 100 μM. The values of E _D ranged between −65 to −68 mV (−66 ± 1.42 mV). The maximum depolarization of E _m was registered approx. 2.5 h after addition of Cd to the perfusion solution and in some cases, partial (Cd > 100 μM) or complete repolarization (Cd < 100 μM) was observed within 8–10 h of Cd treatment. In the time-dependent experiments (0 to 168 h) shortly after the maximum repolarization of E _m a continuous concentration-dependent decrease of E _m followed at all Cd concentrations. Depolarization of E _m was accompanied by both increased electrolyte leakage and inhibition of respiration, especially in the range of 50 μM to 1 mM Cd, with the exception of root cells treated with 1 and 10 μM Cd for 24 and 48 h. Time course analysis of Cd impact on root respiration revealed that at higher Cd concentrations (> 50 μM) the respiration gradually declined (∼ 6 h) and then remained at this lowest level for up to 24 h. All the Cd concentrations used in this experiment induced significant inhibition of root elongation and concentrations higher than 100 μM stopped the root growth within the first day of Cd treatment. Our results suggest that Cd does not cause irreversible changes in the electrogenic plasma membrane H⁺ ATPase because fusicoccin, an H⁺ ATPase activator diminished the depolarizing effect of Cd on the E _m. The depolarization of E _m in the outer cortical cells of maize roots was the result of a cumulative effect of Cd on ATP supply, plasmalemma permeability, and activity of H⁺ ATPase.     

Use of response surface methodology to optimise carotenogenesis in the microalga,Haematococcus pluvialis

The factors controlling biomass production and the synthesis of astaxanthin esters in the microalga Haematococcus pluvialis (CCAP 34/7) have been investigated using a statistical approach employing response surface methodology (RSM). The culture conditions required for optimal growth and carotenogenesis in this alga are very different. Of particular importance is the photon flux density: for growth the optimum is 50–60 μmol m⁻² s⁻¹ whereas the optimum for astaxanthin synthesis is much higher at ∼-1600 μmol m⁻² s⁻¹. The addition of low levels of NaCl to the medium also stimulates to a small extent synthesis of astaxanthin, but photon flux density remains the overriding factor. The optimal temperature for this strain is quite low at 14–15 °C. RSM has been shown to be a rapid and effective technique leading to the optimisation of algal culture conditions. This statistical approach can be applied readily to the majority of microalgae and their products.     

Natural 15N abundance of soil N pools and N2O reflect the nitrogen dynamics of forest soils

Natural ¹⁵N abundance measurements of ecosystem nitrogen (N) pools and ¹⁵N pool dilution assays of gross N transformation rates were applied to investigate the potential of δ¹⁵N signatures of soil N pools to reflect the dynamics in the forest soil N cycle. Intact soil cores were collected from pure spruce (Picea abies (L.) Karst.) and mixed spruce-beech (Fagus sylvatica L.) stands on stagnic gleysol in Austria. Soil δ¹⁵N values of both forest sites increased with depth to 50 cm, but then decreased below this zone. δ¹⁵N values of microbial biomass (mixed stand: 4.7 ± 0.8‰, spruce stand: 5.9 ± 0.9‰) and of dissolved organic N (DON; mixed stand: 5.3 ± 1.7‰, spruce stand: 2.6 ± 3.3‰) were not significantly different; these pools were most enriched in ¹⁵N of all soil N pools. Denitrification represented the main N₂O-producing process in the mixed forest stand as we detected a significant ¹⁵N enrichment of its substrate NO₃⁻ (3.6 ± 4.5‰) compared to NH₄⁺ (−4.6 ± 2.6‰) and its product N₂O (−11.8 ± 3.2‰). In a ¹⁵N-labelling experiment in the spruce stand, nitrification contributed more to N₂O production than denitrification. Moreover, in natural abundance measurements the NH₄⁺ pool was slightly ¹⁵N-enriched (−0.4 ± 2.0 ‰) compared to NO₃⁻ (−3.0 ± 0.6 ‰) and N₂O (−2.1 ± 1.1 ‰) in the spruce stand, indicating nitrification and denitrification operated in parallel to produce N₂O. The more positive δ¹⁵N values of N₂O in the spruce stand than in the mixed stand point to extensive microbial N₂O reduction in the spruce stand. Combining natural ¹⁵N abundance and ¹⁵N tracer experiments provided a more complete picture of soil N dynamics than possible with either measurement done separately.     

Impact of soil vertical water movement on the energy balance of different land surfaces

The soil heat flux determination method proposed by Gao (Boundary-Layer Meteorol 114:165–178, 2005) is discussed for (1) dry surfaces, (2) bare soil or sparse short-grass lands, and (3) dense-grass surfaces or forest. Our analysis shows that, when neglecting the contribution of soil vertical water movement to soil heat flux, the energy components measured independently will (1) still achieve balance over dry surfaces, and (2) be significantly in imbalance over bare soil or sparse short-grass lands. The mean of bare ground evaporation modeled by SiB2 is 1.58 × 10⁻⁵ m³ s⁻¹ m⁻², and the mean of soil water flux obtained by the method of Gao is 1.22 × 10⁻⁵ m³ s⁻¹ m⁻² for the Naqu site in the summer of 1998. Comparison of the bare ground evaporation with the mean of soil water flux shows a difference, the causes of which are investigated. Physically, the bare ground evaporation is equal to the sum of soil water flux and water content change in the soil surface layer. Because the bare ground evaporation is very limited for the dense-grass surfaces or forest, our analysis implies that the energy imbalance encountered over the dense-grass or forest is not caused by the fact that previous researchers neglected soil water movements in their energy budget analyses.     

Modelling the influence of bioturbation on the vertical distribution of sedimentary phosphorus in L. Esrom

A multilayer sediment-water exchange model was used to evaluate the importance of bioturbation in the profundal sediments of L. Esrom. The temporal variation of the vertical distribution of sedimentary phosphorus fractions was modelled with an objective function of 1.50. Deviations between measured and simulated values occurred in the spring, where the measured pool of sedimentary phosphorus sharply declined in the surface sediments. The application of a model for the activity ofChironomus anthracinus based on biomass, oxygen consumption and temperature improved the model in the spring period. The downwards transport of easy-degradable surface sediments reduced the average release of sedimentary phosphorus from 12 mg P · m⁻² · day⁻¹ to 11 mg P · M⁻² · day⁻¹. The introduction of a similar model for the other important burrowing species in L. Esrom,Potamothrix hammoniensis, lowered the objective function to 1.37 and increased the average release to 12.5 mg P · m⁻² · day⁻¹. The minor role of bioturbation in sediment processes is discussed.     

Growth and biomass turnover ofHydrocharis dubia L. cultured under different nutrient conditions

Growth of a floating-leaved plant,Hydrocharis dubia L., was examined under varying nutrient conditions between 0.3 and 30 mgN l⁻¹ total inorganic nitrogen.H. dubia plants cultured under the most nutrient-rich condition showed the highest maximum ramet density (736 m⁻²), the highest maximum biomass (80.4 g dry weight m⁻²), and the highest total net production (185 g dry weight m⁻² in 82 days). Plants under nutrient-poor conditions had a relatively large proportion of root biomass and a small proportion of leaves with a long life span. Compared with other floating-leaved and terrestrial plants, the maximum biomass ofH. dubia was relatively small. This, and the rapid biomass turnover, was related to the short life span of leaves (13.2–18.7 days) and large biomass distribution to leaves.     

Retention of basic electrophysiologic properties by human sweat duct cells in primary culture

Summary The present investigation was undertaken to examine the usefulness of cultured human sweat duct cells for ion transport and related studies in the genetic disease, cystic fibrosis. Electrical properties of cultured duct (CD) cells were compared with electrical properties of microperfused duct (MPD) cells. The resting apical membrane potential (V _a ) of the CD cells was −26.4±0.9 mV,n=158 cells as compared to −24.3±0.6 mV,n=105 of MPD cells. The Na⁺−K⁺ pump inhibitor ouabain, when applied to the apical surface of the CD cells and basolateral surface of MPD cells, depolarized both CD cells (from −28.6±3.6 to −16.8±2.4 mV,n=5) and MPD cells (from −23.8±0.5 mV to −19.5±1.8 mV,n=6). The Na⁺ conductance inhibitor amiloride applied to the apical surface hyperpolarized the apical membrane potentials (V_a) of CD cells and MPD cells by −13.2±1.4 mV,n=43 and −34.3±3.1 mV,n=19), respectively, indicating the presence of amiloride sensitive Na⁺ channels in both groups of cells. However, the amiloride sensitivity of CD cells was dependent on the age of the culture. Cl⁻ substitution at the apical side by the impermeant anion gluconate depolarized the V _a of CD cells and MPD cells by 12.2±0.9 mV,n=32 and 37.9±4.3 mV,n=12, respectively. The effect of β-adrenergic agonist isoproterenol (IPR), was inconsistent. In CD cells, IPR either hyperpolarized (ΔV _a =−8.3±1.2mV,n=5) or depolarized (ΔV _a =8.2±2.3 mV,n=4) or had no effect,n=2. In contrast, most of the MPD cells did not respond to IPR, but three cells had a varied response to IPR. Our results suggest that CD cells, like MPD cells, retain significant Na⁺ and Cl⁻ conductances. CD cells seem to have developed a higher sensitivity to β-adrenergic stimulation in tissue culture as compared to MPD cells. This work was supported by grants from the National Institutes of Health, Bethesda, MD, DK26547, Getty Oil Co., the Gillette Co., Cystic Fibrosis Research Inc., and the U.S. National Cystic Fibrosis Foundation.     

Studies of two Frankia strains isolated from Trevoa trinervis Miers

The Frankia strains TtI 11 and TtI 12 isolated from T. trinervis Miers were characterized regarding their carbon source utilization, intrinsic antibiotic resistance, infectivity, and effectivity on the original host. Both strains grew on BAP medium supplemented with glucose, maltose, and sucrose, but differed in their ability to use other carbon sources such as propionate, pyruvate, acetate, succinate, citrate, and mannitol. The isolates were sensitive to five of the twelve antibiotics tested at 1 μg mL⁻¹ concentration: chloramphenicol, tobramycin, eritromycin, streptomycin, and rifampicin. They exhibited a variable degree of resistance at 1 μg mL⁻¹ concentraction to penicillin G, 4-fluorouracil, oleandomycin, and lincomycin. Both isolates were able to infect and nodulate the original host plant, and thus represent the first reported infective and effective microsymbionts for T. trinervis Miers, a rhamnaceous actinorhizal host. R O D Dixon Section editor     

IAA-induced hyperpolarization of the membrane potential in isolated cells fromMimosa pulvinus

Upon treatment with 10⁻⁴ M IAA the membrane potential of an isolated cell from the main pulvinus, ofMimosa pudica L. depolarized by about 6 mV in 2–5 min, but later it gradually hyperpolarized by about 30 mV. The membrane potential of a motor cell in the main pulvinar tissue hyperpolarized by about 80 mV 1 hr after application of 10⁻⁴ M IAA.