First Few Hours Of Incubation Research Articles

Investigating the Production of Antimicrobial Nanoparticles by Chlorella vulgaris and the Link to Its Loss of Viability.

Chlorella vulgaris from Al-Ahsa, KSA was proved to be an active silver and gold nanoparticle producer. Nanogold and nanosilver particles were characterized using UV-visible spectroscopy, Fourier-transform infrared spectroscopy, and scanning electronmicroscopy. Both nanoparticles were used in the antimicrobial bioassay. The two nanoparticles showed antibacterial activities, with the silver nanoparticles being the most effective. To investigate the argumentative nature of their biosynthesis (i.e., whether it is a biotic or abiotic process), we isolated total ribonucleic acid RNA as an indicator of vitality. RNA was completely absent in samples taken after one week of incubation with silver nitrate and even after one or two days. However, successful extraction was only achievable in samples taken after incubation for one and four hours with silver nitrate. Most importantly, the gel image showed recognizable shearing of the nucleic acid after 4 h as compared to the control. An assumption can be drawn that the synthesis of nanoparticles may start biotically by the action of enzyme(s) and abiotically by action of reducing entities. Nonetheless, with prolonged incubation, excessive nanoparticle accumulation can be deadly. Hence, their synthesis continues abiotically. From the RNA banding profile, we suggest that nanosilver production starts both biotically and abiotically in the first few hours of incubation and then continues abiotically. Nanosilver particles proved to have more of an antimicrobial impact than nanogold and hence are recommended for different applications as antibacterial agents.

Polymer conjugates of doxorubicin bound through an amide and hydrazone bond: Impact of the carrier structure onto synergistic action in the treatment of solid tumours

In this study, we describe the synthesis, physico-chemical characterisation and results of the in vitro and in vivo evaluation of the biological behaviour of N-(2-hydroxypropyl)methacrylamide-based (HPMA) copolymer conjugates bearing doxorubicin (DOX) partly bound via a pH-sensitive hydrazone and partly via enzymatically degradable amide bonds, each contributing to a different anti-tumour mechanism of action of the polymer–doxorubicin conjugate. The following two types of HPMA copolymer drug carriers designed for passive tumour targeting were synthesised and compared: the linear non-degradable copolymer and the biodegradable high-molecular-weight (HMW) diblock copolymer. The HMW diblock copolymer carrier containing a degradable disulphide bond between the polymer blocks showed a rapid degradation in a buffer containing glutathione within the first few hours of incubation. In contrast to the conjugate with the amide bond-bound DOX requiring the presence of lysosomal enzymes to release DOX, the polymer–drug conjugate with the DOX bound via a hydrazone bond released DOX by pH-sensitive hydrolysis, which was significantly faster in a buffer of pH 5.0 (intracellular pH) than pH 7.4, mimicking the conditions in the bloodstream. The significant and comparable in vivo anti-tumour activity of the diblock HMW conjugate and an equimolar mixture of the conjugates differing in the DOX attachment method along with the development of cancer resistance during treatment with these conjugates demonstrated the high potential of these compounds in the development of new nanomedicines suitable for the treatment of solid tumours.

Purified human paraoxonase-1 interacts with plasma membrane lipid rafts and mediates cholesterol efflux from macrophages

Paraoxonase-1 (PON1) is a high-density lipoprotein (HDL)-associated serum enzyme thought to make a major contribution to the antioxidant and anti-inflammatory capacities of HDLs. However, the role of PON1 in the modulation of cholesterol efflux is poorly understood. The aim of our study was to investigate the involvement of PON1 in the regulation of cholesterol efflux, especially the mechanism by which it modulates HDL-mediated cholesterol transport. The enrichment of HDL3 with human PON1 enhanced, in a dose-dependent manner, cholesterol efflux from THP-1 macrophage-like cells and ABCA1-enriched J774 macrophages. Moreover, an additive effect was observed when ABCA1-enriched J774 macrophages were incubated with both PON1 and apo-AI. Interestingly, PON1 alone was able to mediate cholesterol efflux from J774 macrophages and to upregulate ABCA1 expression on J774 macrophages. Immunofluorescence measurement showed an increase in PON1 levels in the cytoplasm of J774 macrophages overexpressing ABCA1. PON1 used an apo-AI-like mechanism to modulate cholesterol efflux from rapid and slow efflux pools derived from the lipid raft and nonraft domains of the plasma membrane, respectively. This was supported by the fact that ABCA1 protein was incrementally expressed by J774 macrophages within the first few hours of incubation with cholesterol-loaded J774 macrophages and that cyclodextrin significantly inhibited the capacity of PON1 to modulate cholesterol efflux from macrophages. This finding suggested that PON1 plays an important role in the antiatherogenic properties of HDLs and may exert its protective function outside the lipoprotein environment.

Denitrification in Suburban Lawn Soils

There is great uncertainty about the fate of nitrogen (N) added to urban and suburban lawns. We used direct flux and in situ chamber methods to measure N and NO fluxes from lawns instrumented with soil O sensors. We hypothesized that soil O, moisture, and available NO were the most important controls on denitrification and that N and NO fluxes would be high following fertilizer addition and precipitation events. While our results support these hypotheses, the thresholds of soil O, moisture, and NO availability required to see significant N fluxes were greater than expected. Denitrification rates were high in saturated, fertilized soils, but low under all other conditions. Annual denitrification was calculated to be 14.0 ± 3.6 kg N ha yr, with 5% of the growing season accounting for >80% of the annual activity. Denitrification is thus an important means of removing reactive N in residential landscapes, but varies markedly in space, time, and with factors that affect soil saturation (texture, structure, compaction) and NO availability (fertilization). Rates of in situ NO flux were low; however, when recently fertilized soils saturated with water were incubated in the laboratory, we saw extraordinarily high rates of NO production for the first few hours of incubation, followed by rapid NO consumption later in the experiment. These findings indicate a lag time between accelerated NO production and counterbalancing increases in NO consumption; thus, we cannot yet conclude that lawns are an insignificant source of NO in our study area.

Group‐specific primary production based on stable‐isotope labeling of phospholipid‐derived fatty acids

Stable‐isotope labeling of phospholipid‐derived fatty acids (PLFAs) is a potentially powerful technique to study group‐specific primary production of phytoplankton, as many algal groups possess a specific PLFA composition, and it is relatively simple to measure the isotopic composition of a large number of PLFAs. Experiments with cultured algae showed that differences exist in labeling among PLFAs and between PLFAs and particulate organic carbon (POC), most likely owing to differences in biosynthesis pathways causing some components of the cell with short pathways to be labeled faster. These differences were constant, however, during the first few hours of incubation, and correction factors were used to convert PLFA labeling to total carbon uptake. In algal cultures, growth rates based on 13C‐PLFA labeling agreed well with those based on biomass increases in terms of PLFA concentrations and cell numbers. At two contrasting sites in the Scheldt estuary, PLFA synthesis rates were calculated using 2‐h incubations. Group‐specific primary production was estimated from PLFA synthesis rates and PLFA compositional spectra of samples and algal taxa using the matrix factorization program Chemtax. When accompanied with studies or information on system‐relevant phytoplankton, this sensitive method will be applicable to a wide range of pelagic ecosystems and also to benthic systems such as algal mats.

Changes in interfacial properties of α-synuclein preceding its aggregation

Parkinson's disease (PD) is associated with the formation and deposition of amyloid fibrils of the protein alpha-synuclein (AS). It has been proposed that oligomeric intermediates on the pathway to fibrilization rather than the fibrils themselves are the pathogenic agents of PD, but efficient methods for their detection are lacking. We have studied the interfacial properties of wild-type AS and the course of its aggregation in vitro using electrochemical analysis and dynamic light scattering. The oxidation signals of tyrosine residues of AS at carbon electrodes and the ability of fibrils to adsorb and catalyze hydrogen evolution at hanging mercury drop electrodes (HMDEs) decreased during incubation. HMDEs were particularly sensitive to pre-aggregation changes in AS. Already after 1 h of a standard aggregation assay in vitro (stirring at 37 degrees C), the electrocatalytic peak H increased greatly and shifted to less negative potentials. Between 3 and 9 h of incubation, an interval during which dynamic light scattering indicated AS oligomerization, peak H diminished and shifted to more negative potentials, and AS adsorbability decreased. We tentatively attribute the very early changes in the interfacial behavior of the protein after the first few hours of incubation to protein destabilization with disruption of long-range interactions. The subsequent changes can be related to the onset of oligomerization. Our results demonstrate the utility of electrochemical methods as new and simple tools for the investigation of amyloid formation.

Uptake of Spartina-derived humic nitrogen by estuarine phytoplankton in nonaxenic and axenic culture

Humic substances are a collection of colored organic acids characterized by high molecular weight and low nitrogen (N) content that are thought to be biologically recalcitrant. We examined a suite of nonaxenic estuarine phytoplankton isolates to determine their ability to take up 15N-labeled humic substances formed in the laboratory and supplied as the sole N source. All 17 estuarine and coastal strains took up the added humic N, but the one polar isolate did not. Two of the coastal isolates (Heterosigma akashiwo and Fibrocapsa japonica) could take up the humic N in nonaxenic culture but not in axenic culture, suggesting that bacterial remineralization played a role in making humic N accessible to these species. The ability of nonaxenic phytoplankton isolates to use humics of different ages (1 week to 1 yr old) was tested using three strains capable of taking up humic N at high rates. Younger, fresher humics were taken up by the phytoplankton strains at higher rates than older, more fulvic-like compounds, and at rates higher than inorganic N uptake run in parallel. Time-course results indicate that while uptake of the inorganic N forms was sustained, high rates of humic N uptake declined after the first few hours of incubation. Additional humic substances were labeled with both 15N and 13C, and the relative incorporation of N versus carbon (C) was used to infer potential uptake mechanisms. None of the isolates took up humic C, suggesting that uptake of the humic N followed breakdown of the humic molecule by bacteria or via extracellular enzyme cleavage of humic N. Regardless of the mode of uptake, the observation that humic N can be rapidly used by phytoplankton suggests that the importance of humic N as a source of phytoplankton N nutrition should be reevaluated.

Cell death in Escherichia coli dnaE(Ts) mutants incubated at a nonpermissive temperature is prevented by mutation in the cydA gene.

Cells of the Escherichia coli dnaE(Ts) dnaE74 and dnaE486 mutants die after 4 h of incubation at 40 degrees C in Luria-Bertani medium. Cell death is preceded by elongation, is inhibited by chloramphenicol, tetracycline, or rifampin, and is dependent on cell density. Cells survive at 40 degrees C when they are incubated at a high population density or at a low density in conditioned medium, but they die when the medium is supplemented with glucose and amino acids. Deletion of recA or sulA has no effect. We isolated suppressors which survived for long periods at 40 degrees C but did not form colonies. The suppressors protected against hydroxyurea-induced killing. Sequence and complementation analysis indicated that suppression was due to mutation in the cydA gene. The DNA content of dnaE mutants increased about eightfold in 4 h at 40 degrees C, as did the DNA content of the suppressed strains. The amount of plasmid pBR322 in a dnaE74 strain increased about fourfold, as measured on gels, and the electrophoretic pattern appeared to be normal even though the viability of the parent cells decreased 2 logs. Transformation activity also increased. 4',6'-diamidino-2-phenylindole staining demonstrated that there were nucleoids distributed throughout the dnaE filaments formed at 40 degrees C, indicating that there was segregation of the newly formed DNA. We concluded that the DNA synthesized was physiologically competent, particularly since the number of viable cells of the suppressed strain increased during the first few hours of incubation. These observations support the view that E. coli senses the rate of DNA synthesis and inhibits septation when the rate of DNA synthesis falls below a critical level relative to the level of RNA and protein synthesis.

Evaluation of Thin Agar Layer Method for Recovery of Acid-Injured Foodborne Pathogens

The thin agar layer (TAL) method of Kang and Fung was used to enumerate acid-injured foodborne pathogens. This method involves overlaying 14 ml of nonselective medium (tryptic soy agar [TSA]) onto a prepoured and solidified pathogen-specific, selective medium in a petri dish. After surface plating, injured cells resuscitated and grew on TSA during the first few hours of incubation; then, the selective agents from the selective medium diffused to the top layer, interacted with the recovered microorganisms, and started to produce typical reactions. Foodborne pathogens were exposed to 2% acetic acid for 1, 2, or 4 min, and the recovery rate with the TAL method was compared with the rate of TSA and pathogen-specific, selective media. No significant difference occurred between TSA and TAL (P > 0.05) for enumeration of acid-injured Escherichia coli O157:H7, Salmonella Typhimurium, Staphylococcus aureus, and Yersinia enterocolitica, and both recovered significantly higher numbers than the selective medium for each respective pathogen (P < 0.05). For recovery of acid-injured Listeria monocytogenes, no difference (P > 0.05) occurred among TSA, TAL, and selective media. However, fewer cells were recovered in the selective media. The TAL method is a one-step, convenient procedure for recovery of acid-injured cells.

Test-tube simulated lipofuscinogenesis. Effect of oxidative stress on autophagocytotic degradation

Cysteine-stimulated oxidation of a rat liver lysosomal-mitochondrial fraction (LMF) was studied. The process would simulate oxidative stress-related events during the degradation of autophagocytosed material within secondary lysosomes, which may contribute to the formation of lipofuscin or age pigment. Millimolar concentration of cysteine was needed to stimulate LMF lipid peroxidation, measured as thiobarbituric acid reactive substances (TBARS). The amount of endogenous LMF iron was 545 μg/l and was enough to initiate peroxidation, probably through the reduction of ferric to ferrous iron by cysteine with induction of Fenton chemistry. Peroxidation could be completely inhibited by the addition of the iron chelator desferal or the antioxidant BHT. A substantial amount of the formed TBARS was associated with trichloroacetic acid (TCA) precipitable proteins. Elevated protein carbonyls was observed 1–2 h after the increase of TBARS. The tryptophan-tyrosine related protein autofluorescence ( 280 335 nm ) decreased sharply during the first few hours of incubation. In contrast, a lipofuscin-type autofluorescence ( 345 430 nm ) appeared only after a few days, suggesting that the latter fluorophore is not an immediate product of protein oxidation. The sequential formation of TBARS, protein carbonyls and lipofuscin-type autofluorescence as well as their dependence on iron and a reducing agent add further support to the concept that lipofuscin forms in secondary lysosomes as a result of iron-catalyzed oxidative reactions involving autophagocytosed materials.

Lipoproteins activate acyl-coenzyme A:cholesterol acyltransferase in macrophages only after cellular cholesterol pools are expanded to a critical threshold level.

Activation of acyl-CoA:cholesterol actyltransferase (ACAT) in macrophages by lipoproteins is a key event in atheroma foam cell formation. To help elucidate the mechanisms whereby lipoproteins stimulate ACAT, the early cellular events of lipoprotein-induced ACAT stimulation were studied in mouse peritoneal macrophages. As a function of increasing lipoprotein-cholesterol influx to the cell during the first few hours of incubation, ACAT activity was markedly stimulated by beta-very low density lipoprotein (beta-VLDL) and acetyl-low density lipoprotein (acetyl-LDL) only after lipoprotein-cholesterol influx reached a threshold level of approximately 25% above the basal cell cholesterol content. In contrast, LDL stimulated ACAT only minimally at this level of lipoprotein-cholesterol influx. In further experiments, the source of ACAT cholesterol substrate during the initial stimulation of ACAT was shown to be a mixture of cellular (approximately 75%) and lipoprotein-cholesterol (approximately 25%) in proportions that approximated the proportions of originally cellular and lipoprotein-cholesterol in the cell. Thus, lipoprotein-cholesterol rapidly mixed with most or all of cellular cholesterol before ACAT esterification. Additional studies showed that LDL caused significant efflux of cellular cholesterol, thus providing at least a partial explanation for the relatively weak ACAT stimulatory potential of LDL. To support this idea, LDL that was modified to decrease its ability to induce net cellular cholesterol efflux stimulated ACAT 2-fold greater than control LDL when matched for lysosomal LDL-cholesterol influx. Moreover, when the effective efflux potentials of beta-VLDL and acetyl-LDL were increased, ACAT stimulation was markedly decreased despite unchanged lipoprotein-cholesterol influx. Thus, macrophage ACAT is stimulated not directly by the influx of newly hydrolyzed lipoprotein-cholesterol but rather by net expansion of cellular cholesterol pools to a particular threshold level. This scheme has potentially important implications regarding the cellular and molecular mechanisms of foam cell formation.

Dimethyl Sulfide Production from Dimethylsulfoniopropionate in Coastal Seawater Samples and Bacterial Cultures

Dimethyl sulfide (DMS) was produced immediately after the addition of 0.1 to 2 muM beta-dimethylsulfonio-propionate (DMSP) to coastal seawater samples. Azide had little effect on the initial rate of DMS production from 0.5 muM added DMSP, but decreased the rate of production after 6 h. Filtration of water samples through membrane filters (pore size, 0.2 mum) greatly reduced DMS production for approximately 10 h, after which time DMS production resumed at a high rate. Autoclaving completely eliminated the production of DMS. The antibiotics chloramphenicol, tetracycline, kanamycin, and vancomycin all had little effect on the accumulation of DMS over the first few hours of incubation, but produced significant inhibition thereafter. The effects of individual antibiotics were additive. Chloroform over a range of concentrations (0.25 to 1.25 mM) had no effects on DMS production. Similarly, organic amendments, including acrylate, glucose, protein, and starch, did not affect DMS accumulation from DMSP. Acrylate, a product of the enzymatic cleavage of DMSP, was metabolized in seawater samples, and two strains of bacteria were isolated with this compound as the growth substrate. These bacteria produced DMS from DMSP. The sensitivity to inhibitors with respect to growth and DMSP-lyase activity varied from strain to strain. These results illustrate the significant potential for microbial conversion of dissolved DMSP to DMS in coastal seawater.

Antibacterial effect of meropenem and imipenem on Proteus mirabilis

Phase-contrast microscopy, killing-curves and turbidimetric growth-curves were used in a comparative study of the antibacterial effects of a new carbapenem, meropenem (SM 7338) and imipenem on five strains of Proteus mirabilis. Despite the low MIC (0.2 mg/l) of imipenem for the five strains included in our study, the MBC remained relatively high (4.4 mg/l). During the first few hours of incubation, imipenem induced large lemon-shaped cells while the turbidity increased without substantial changes in culture viability. Later, most of the cell-wall deficient bacteria generated small spheroplasts until the antibiotic concentration exceeded 32 times the MIC. The MIC of meropenem was lower (0.03 mg/l) with an MBC (0.08 mg/l) very close to the MIC. Meropenem also induced large bodies but these cell-wall deficient bacteria did not generate small round bodies as observed with imipenem. In conclusion, imipenem produced in strains of Pr. mirabilis an amdinocillin-like change in cell morphology, responsible for the discrepancies observed between MIC and MBC. This effect was not observed with meropenem.

Synergistic effect of phorbol myristate acetate on bacterial lipopolysaccharide induced rat splenocyte proliferation

1. 1. Bacterial lipopolysaccharide (LPS) stimulated [ 3H]TdR incorporation of rat splenocytes in a concentration dependent manner. 2. 2. Phorbol 12-myristate 13-acetate (PMA) alone has little effect on rat splenocyte proliferation but it exerted a marked synergistic effect on LPS-induced [ 3H]TdR incorporation when added at the first few hours of incubation with LPS. Minimal synergistic effect of PMA was observed if it was added later than 4 hr after LPS application. 3. 3. Both LPS-stimulated and PMA synergized incorporation of [ 3H]TdR in rat splenocytes were inhibited by H-7, a protein kinase C inhibitor. 4. 4. The results support the notion that the activation of protein kinase C is a necessary but insufficient cellular signal in the initiation of proliferative response of rat splenocytes by LPS.

The course of steroid release by intact ovarian follicles of atlantic salmon ( Salmo salar) incubated in vitro with and without gonadotrophin

Intact ovarian follicles were dissected from a single ovary and groups of follicles incubated in balanced saline at 6° with and without a pacific salmon gonadotrophin (GTH) preparation. Aliquots of the incubation media were withdrawn at intervals, the steroids were extracted with solvent, and 17α, 20β-dihydroxy-4-pregnen-3-one (17α20βP), 17α-hydroxyprogesterone, progesterone, androstenedione, testosterone, and oestradiol were separated chromatographically and measured by radioimmunoassay. The main findings were (1) germinal vesicle breakdown commenced on Day 8 under the influence of GTH, (2) after an induction period of about 2 days there was a dramatic and continuing release of 17α20βP in the presence of GTH, (3) GTH promoted a moderate release of 17α-hydroxyprogesterone, (4) GTH stimulated testosterone release up to Day 6 but thereafter levels fell, reflecting either absorption or catabolism of the released steroid, (5) GTH induced a precipitous release of androstenedione during the first few hours of incubation, and (6) progesterone and oestradiol release were little affected by GTH. Steroid concentrations were also measured in ova stripped from naturally ovulating wild fish and the relative amounts were shown to bear some similarity to those released into the incubation medium in the presence of GTH. The routes of biosynthesis and functions of these steroids are considered in light of the results.

Primary hypoblast development in the chick : II. The role of cell division.

Proliferative patterns in colchicine treated embryos during the first few hours of incubation, Eyal-Giladi and Kochav stages XI-XIII, clarify the role of cell division in the anterolateral expansion of the primary hypoblast as well as the expansion of the entire blastoderm. A layer of primary hypoblast (extra-embryonic endoderm) can form in the absence of cell division. Colchicine, in concentrations used here, does not prevent ingression of cells from the upper layer to the primary hypoblast and establishment of intercellular contacts. These processes, however modified, remain sufficiently operative so that a hypoblast layer forms. In addition, colchicine does not prevent radial expansion of the whole blastoderm. The demonstrated distribution of proliferative rates in the blastoderm can be the source of cells for blastoderm radial expansion, shape changes and for hypoblast development supplementing ingression of cells from the upper layer.

Macrophage-lymphocyte clusters in the immune response to soluble protein antigen in vitro. VIII. Cinephotomicrographic studies.

T cells from immune guinea-pigs produce clusters in vitro with macrophages pulsed with soluble protein antigens. The formation of clusters is antigen-specific. Time-lapse cinephotomicrography was used to study the sequence of events leading to cluster formation and the kinetics of already formed clusters. The central lymphocyte attaches through a broad base to the macrophage during the first few hours of incubation. After several hours, during which the central lymphocyte is situated alone on the surface of the macrophage, free lymphocytes begin to interact for shorter or longer periods of time through their uropods with the central lymphocyte, thus acting as peripheral lymphocytes. In spite of a frequent traffic of peripheral lymphocytes in and out, the cluster is a relatively stable structure. Occasionally the entire complex of lymphocytes leaves the macrophage, moves randomly in the culutre and attaches to a new macrophage or returns to the same macrophage.

64Cu metabolism in Menkes and normal cultured skin fibroblasts.

Summary: The amount of radioactivity accumulated in normal skin fibro-blasts cultured in the presence of 64Cu increased during the first few hours of incubation, and reached a plateau after 18 hr. Fibroblasts from patients with Menkes syndrome continued to accumulate 64Cu and after 48 hr, the mutant cells contained over 3 times more radioactivity than the normal cells. Normal skin fibroblasts grown in the presence of 64Cu for 24 hr and chased for 6 and 24 hr with 64Cu-free medium released 78% and 91% of the radioactivity, respectively, whereas Menkes fibroblasts grown under similar conditions released only 22% and 51%, respectively. The amount of radioactivity incorporated by fibroblasts increased with increasing concentrations of 64Cu in the culture medium, but the Menkes fibroblasts incorporated more 64Cu than normal fibroblasts. A slight reduction in the incorporation and efflux of 64Cu was seen with several metabolic inhibitors, but there was no difference between normal and mutant cells. Treatment of labeled cells with trypsin did not affect the amount of 64Cu picked up by the cells. Most of the radioactive copper incorporated by the cells was not precipitated by trichloroacetic acid or phosphotungstic acid, although the percentage of precipitated 64Cu was consistently higher in normal than in Menkes fibroblasts. Most of the 64Cu was bound to a molecule with a molecular weight of about 10,000, whereas a small fraction, proportionally higher in normal cells, was bound to a large molecular weight component(s). The amount of 64Cu bound to the small molecular weight species was significantly greater in Menkes fibroblasts than in normal cells. Menkes fibroblasts were more sensitive to high nonphysiologic levels of nonradioactive copper than were normal cells. These findings demonstrate pronounced metabolic differences between normal and Menkes fibroblasts and indicate the need for further studies before proper treatment of this disease can be instituted. Speculation: Copper picked up by cultured skin fibroblasts is preferentially bound to a molecule with a molecular weight of about 10,000. The increased copper accumulation in Menkes fibroblasts may be caused by the deficiency of an enzyme that catalyzes the cleavage of this bond, by the presence of an increased amount of this small molecular weight molecule in the mutant cells, or by an increased binding capacity of this molecule for copper.

Effect of incubation temperature on the development of lactic acid bacteria and their phages

SummaryThirty-one strains of mesophilic and thermophilic lactic acid bacteria and their respective phages were tested for their minimum, optimum and maximum multiplication temperatures. Culture growth was strongly influenced by temperature during the first few hours of incubation, but less so after 24 h. Most of the phages showed the same pattern of development as their hosts, but one phage lysing a thermophilic lactobacillus and 3 phages lysing mesophilic streptococci proved temperature-sensitive, having a lower maximum temperature than that of their hosts. One phage was unusual in that its minimum development temperature was 7 °C above that of its host. Differences in temperature sensitivity were insufficient to reduce risk of phage infection by temperature control in industrial processes.

Stimulation of Ethylene Production in the Mung Bean Hypocotyls by Cupric Ion, Calcium Ion, and Kinetin

The synergistic stimulation of ethylene production by kinetin and Ca(2+) in hypocotyl segments of mung bean (Phaseolus aureus Roxb.) seedling was further studied. The requirement for Ca(2+) in this system was specific. Except for Sr(2+), which mimicked the effect of Ca(2+), none of the following divalent cations, including Ba(2+), Mg(6+), Cu(2+), Hg(2+), Co(2+), Ni(2+), Sn(2+), and Zn(2+), showed synergism with kinetin on ethylene production. Fe(2+), however, showed a slight synergism with kinetin. Some of them (Hg(2+), Co(2+), and Ni(2+)) had a strong inhibitory effect, while others (Zn(2+), Mg(2+), Sn(2+), and Ba(2+)) had a slight or no inhibitory effect on ethylene production in the absence or presence of kinetin.Cu(2+) alone, depending on the concentration applied, stimulated ethylene production with a lag period of about 2 hours and had no synergism with kinetin on ethylene production. When Cu(2+) was applied with Ca(2+), a remarkable synergistic stimulation of ethylene production was observed. Tracer experiments indicated that Cu(2+) enhanced the uptake of (45)Ca(2+) into the tissues during the first few hours of incubation, and this increase of (45)Ca(2+) uptake paralleled the enhancement of ethylene production. When Ca(2+) was applied together with kinetin plus Cu(2+), both the ethylene production and the (45)Ca(2+) uptake were greatly increased over those from the segments treated with Cu(2+) or kinetin alone. The increase in ethylene production as a result of kinetin plus Ca(2+) plus Cu(2+) treatment is equal to the combined increases caused by kinetin plus Ca(2+) and Cu(2+) plus Ca(2+). A possible mechanism accounting for such cooperative effects of Cu(2+), Ca(2+), and kinetin on ethylene production is discussed.