Comparison of temperature effects on soil respiration and bacterial and fungal growth rates

Temperature is an important factor regulating microbial activity and shaping the soil microbial community. Little is known, however, on how temperature affects the most important groups of the soil microorganisms, the bacteria and the fungi, in situ. We have therefore measured the instantaneous total activity (respiration rate), bacterial activity (growth rate as thymidine incorporation rate) and fungal activity (growth rate as acetate-in-ergosterol incorporation rate) in soil at different temperatures (0-45 degrees C). Two soils were compared: one was an agricultural soil low in organic matter and with high pH, and the other was a forest humus soil with high organic matter content and low pH. Fungal and bacterial growth rates had optimum temperatures around 25-30 degrees C, while at higher temperatures lower values were found. This decrease was more drastic for fungi than for bacteria, resulting in an increase in the ratio of bacterial to fungal growth rate at higher temperatures. A tendency towards the opposite effect was observed at low temperatures, indicating that fungi were more adapted to low-temperature conditions than bacteria. The temperature dependence of all three activities was well modelled by the square root (Ratkowsky) model below the optimum temperature for fungal and bacterial growth. The respiration rate increased over almost the whole temperature range, showing the highest value at around 45 degrees C. Thus, at temperatures above 30 degrees C there was an uncoupling between the instantaneous respiration rate and bacterial and fungal activity. At these high temperatures, the respiration rate closely followed the Arrhenius temperature relationship.     

Lipase immobilized by adsorption

Summary Candida cylindraceae lipase was immobilized by adsorption to various hydrophilic and hydrophobic supports and studied with respect to the esterification rates of a primary and a secondary alcohol, respectively, in organic media. The reaction rates were compared with the rate of esterification with free lipase. When the secondary alcohol, (R, S)-1-phenylethanol, was used the highest reaction rates were measured for lipase adsorbed to the hydrophobic supports. When the primary alcohol, heptanol, was used free lipase exhibited the highest reaction rate. A kinetic explantation of these results is proposed.     

Septicemia due to Streptococcus mitis in neutropenic patients with acute leukemia

Eight neutropenic patients with acute lymphocytic or nonlymphocytic leukemia had septicemia due to different strains of Streptococcus mitis (St. mitis), a microorganism not commonly recognized as a special pathogen in leukemic patients. Four of the patients had been treated with high-dose cytosine arabinoside as part of the cytostatic regimen, six had a central venous line and four patients had oral lesions prior to the infection. Selective gut decontamination consisted of co-trimoxazole/colistin in five patients and quinolones in three patients. The first three patients died, either due to interstitial pneumonia with the adult respiratory distress syndrome (ARDS), or due to infection-triggered disseminated intravascular coagulation despite prompt empiric antibiotic therapy including vancomycin. The other patients improved after empiric supplementation of penicillin G (30 Mega/day) to the antibiotic regimen. Beginning ARDS in two of these patients dramatically responded to high-dose steroids. We conclude that St. mitis is a major pathogen in neutropenic leukemic patients. Infection appears to occur independently of acute leukemic cell type, regimen of selective gut decontamination, venous access, visible oral lesions or treatment with high-dose cytosine arabinoside. The clinical course of our patients raises questions about the value of commonly recommended empiric antibiotic regimens, which were clearly ineffective to control infections with St. mitis in this patient group. Our data indicate that immediate antibiotic therapy with penicillin G is indicated and may be life-saving for suspected St. mitis infections in neutropenic leukemic patients.     

Transesterification with Candida Cylindracea Lipase in a Biphasic Aqueous-Organic System. Dependence of the Enantiomeric Ratio and the Reaction Rate on the Proportions of Water and Cyclohexane

18 September 1989

A transesterification reaction between 1-phenyl ethyl butyrate and 1-heptanol was carried out with Candida cylindracea lipase. The reaction was studied, with respect to the reaction rate and the enantiomeric ratio at different proportions of water and cyclohexane. A significantly lower reaction rate was observed for incubations with less than 0.5% water compared with those at a higher water content. Transesterification dominated over hydrolysis as the main reaction even at 70% water and a dramatic increase of the enantioselectivity was observed at this high water content. It is proposed that these effects depend on the mechanism of lipase catalysis at the interface of emulsion droplets. This interface binding gives 1-heptanol a positional preference compared with water for nucleophilic attack of the acyl enzyme and may, in addition, induce an optimal conformation for high enantioselectivity of the enzyme.     

Quantification of mycoparasitism by the nematode-trapping fungus Arthrobotrys oligospora on Rhizoctonia solani and the influence of nutrient levels

Abstract The influence of nutrient level, type of carbon source and nitrogen concentration on the parasitism of Arthrobotrys oligospora on Rhizoctonia solani were investigated by quantification of coiling frequency. Changes in coiling frequency were also compared with changes in hyphal density and colony radial growth rate. Increasing concentrations of corn meal agar gave increasing coiling frequency up to a concentration of half the recomended strength. At higher concentrations the coiling frequency was constant, although the hyphal density of both fungi increased over the whole concentration range. Coiling frequency was positively correlated with the probability of hyphal encounter, calculated as the product of the hyphal densities of the two fungi, except at high CMA concentrations. Amongst several carbohydrates tested, glucose resulted in the highest, and sucrose the lowest, coiling frequency. The effect of the different carbohydrates on coiling frequency was not correlated with the hyphal densities of the fungi. Addition of a nitrogen source, NaNO₃, removed the differences in coiling frequency between glucose and sucrose and increased coiling frequencies on both sugars.     

A new balancing act: The many roles of melatonin and serotonin in plant growth and development

Melatonin and serotonin are indoleamines first identified as neurotransmitters in vertebrates; they have now been found to be ubiquitously present across all forms of life. Both melatonin and serotonin were discovered in plants several years after their discovery in mammals, but their presence has now been confirmed in almost all plant families. The mechanisms of action of melatonin and serotonin are still poorly defined. Melatonin and serotonin possess important roles in plant growth and development, including functions in chronoregulation and modulation of reproductive development, control of root and shoot organogenesis, maintenance of plant tissues, delay of senescence, and responses to biotic and abiotic stresses. This review focuses on the roles of melatonin and serotonin as a novel class of plant growth regulators. Their roles in reproductive and vegetative plant growth will be examined including an overview of current hypotheses and knowledge regarding their mechanisms of action in specific responses.     

Comparison of bone and renal effects in HIV-infected adults switching to abacavir or tenofovir based therapy in a randomized trial

Introduction

Our objective was to compare the bone and renal effects among HIV-infected patients randomized to abacavir or tenofovir-based combination anti-retroviral therapy.

Methods

In an open-label randomized trial, HIV-infected patients were randomized to switch from zidovudine/lamivudine (AZT/3TC) to abacavir/lamivudine (ABC/3TC) or tenofovir/emtricitabine (TDF/FTC). We measured bone mass density (BMD) and bone turnover biomarkers (osteocalcin, osteocalcin, procollagen type 1 N-terminal propeptide (P1NP), alkaline phosphatase, type I collagen cross-linked C-telopeptide (CTx), and osteoprotegerin). We assessed renal function by estimated creatinine clearance, plasma cystatin C, and urinary levels of creatinine, albumin, cystatin C, and neutrophil gelatinase-associated lipocalin (NGAL). The changes from baseline in BMD and renal and bone biomarkers were compared across study arms.

Results

Of 40 included patients, 35 completed 48 weeks of randomized therapy and follow up. BMD was measured in 33, 26, and 27 patients at baseline, week 24, and week 48, respectively. In TDF/FTC-treated patients we observed significant reductions from baseline in hip and lumbar spine BMD at week 24 (−1.8% and −2.5%) and week 48 (−2.1% and −2.1%), whereas BMD was stable in patients in the ABC/3TC arm. The changes from baseline in BMD were significantly different between study arms. All bone turnover biomarkers except osteoprotegerin increased in the TDF/FTC arm compared with the ABC/3TC arm, but early changes did not predict subsequent loss of BMD. Renal function parameters were similar between study arms although a small increase in NGAL was detected among TDF-treated patients.

Conclusion

Switching to TDF/FTC-based therapy led to decreases in BMD and increases in bone turnover markers compared with ABC/3TC-based treatment. No major difference in renal function was observed.

Trial registration

Clinicaltrials.gov {"type":"clinical-trial","attrs":{"text":"NCT00647244","term_id":"NCT00647244"}}NCT00647244     

Compaction of forest soil by logging machinery favours occurrence of prokaryotes

Soil compaction caused by passage of logging machinery reduces the soil air capacity. Changed abiotic factors might induce a change in the soil microbial community and favour organisms capable of tolerating anoxic conditions. The goals of this study were to resolve differences between soil microbial communities obtained from wheel-tracks (i.e. compacted) and their adjacent undisturbed sites, and to evaluate differences in potential anaerobic microbial activities of these contrasting soils. Soil samples obtained from compacted soil had a greater bulk density and a higher pH than uncompacted soil. Analyses of phospholipid fatty acids demonstrated that the eukaryotic/prokaryotic ratio in compacted soils was lower than that of uncompacted soils, suggesting that fungi were not favoured by the in situ conditions produced by compaction. Indeed, most-probable-number (MPN) estimates of nitrous oxide-producing denitrifiers, acetate- and lactate-utilizing iron and sulfate reducers, and methanogens were higher in compacted than in uncompacted soils obtained from one site that had large differences in bulk density. Compacted soils from this site yielded higher iron-reducing, sulfate-reducing and methanogenic potentials than did uncompacted soils. MPN estimates of H2-utilizing acetogens in compacted and uncompacted soils were similar. These results indicate that compaction of forest soil alters the structure and function of the soil microbial community and favours occurrence of prokaryotes.     

Tools for conservation of Balsamorhiza deltoidea and Balsamorhiza sagittata: Karrikin and thidiazuron-induced growth

Wildfires are having both devastating and regenerative impacts on the ecosystems in the Pacific Northwest of North America. Balsamorhiza sagittata and B. deltoidea (balsamroot) are ecologically important species in this region, and B. sagittata populations are increasing, while B. deltoidea is critically imperiled. The aim of this research was to establish in vitro protocols for germination and regeneration of Balsamorhiza spp. to enable conservation efforts. It was hypothesized that karrikins, which are plant growth regulators released from burning plants during wildfires, would induce seed germination in Balsamorhiza spp. Three karrikins (KAR₁, KAR₂, and KAR₁₁) were tested for the ability to enhance germination in these species at two levels (5 or 10 μM). KAR₂ had the strongest positive effect on germination and induced 47% and 60% germination, respectively, in B. sagittata seeds compared to 14% germination obtained in the control (water agar media). In B. deltoidea, KAR₂ treatment resulted in a germination rate of 73.1% and 100%, compared to 69% in the control. A germplasm collection of seedlings of both species was established for conservation and regeneration experiments. Thidiazuron treatment (10 μM) induced formation of embryo-like structures in seedlings of both B. sagittata and B. deltoidea, with regenerants originating from the crown of seedlings. The present study provides in vitro methods for conservation and mass propagation of Balsamorhiza species.