Effects of elevated atmospheric CO2 concentrations on soil microorganisms

Effects of elevated CO(2) on soil microorganisms are known to be mediated by various interactions with plants, for which such effects are relatively poorly documented. In this review, we summarize and synthesize results from studies assessing impacts of elevated CO(2) on soil ecosystems, focusing primarily on plants and a variety the of microbial processes. The processes considered include changes in microbial biomass of C and N, microbial number, respiration rates, organic matter decomposition, soil enzyme activities, microbial community composition, and functional groups of bacteria mediating trace gas emission such as methane and nitrous oxide. Elevated CO(2) in atmosphere may enhance certain microbial processes such as CH(4) emission from wetlands due to enhanced carbon supply from plants. However, responses of extracellular enzyme activities and microbial community structure are still controversy, because interferences with other factors such as the types of plants, nutrient availabilitial in soil, soil types, analysis methods, and types of CO(2) fumigation systems are not fully understood.     

Effects of low urea concentrations on protein-water interactions

Solvent properties of aqueous media (dipolarity/polarizability, hydrogen bond donor acidity, and hydrogen bond acceptor basicity) were measured in the coexisting phases of Dextran–PEG aqueous two-phase systems (ATPSs) containing .5 and 2.0 M urea. The differences between the electrostatic and hydrophobic properties of the phases in the ATPSs were quantified by analysis of partitioning of the homologous series of sodium salts of dinitrophenylated amino acids with aliphatic alkyl side chains. Furthermore, partitioning of eleven different proteins in the ATPSs was studied. The analysis of protein partition behavior in a set of ATPSs with protective osmolytes (sorbitol, sucrose, trehalose, and TMAO) at the concentration of .5 M, in osmolyte-free ATPS, and in ATPSs with .5 or 2.0 M urea in terms of the solvent properties of the phases was performed. The results show unambiguously that even at the urea concentration of .5 M, this denaturant affects partitioning of all proteins (except concanavalin A) through direct urea–protein interactions and via its effect on the solvent properties of the media. The direct urea–protein interactions seem to prevail over the urea effects on the solvent properties of water at the concentration of .5 M urea and appear to be completely dominant at 2.0 M urea concentration.     

Effects of diffusion limitation on immobilized nitrifying microorganisms at low temperatures

Activation energies of suspended and immobilized nitrifying bacteria were determined and compared to determine if diffusion limitation results in decreased sensitivity for temperature. The activation energy for the respiration activity of suspended Nitrosomonas europaea and Nitrobacter agilis was found to be 86.4 and 58.4 kJ mol(-1), respectively. The activation energy for oxygen diffusion in the support material, kappa-carrageenan, determined from the effect of temperature on the effective diffusion coefficient (D), was 17.2 kJ mol(-1). Consequently, the apparent actvation energy of diffusion limited cells should be lower. It was indeed shown that due to the effect of diffusion limitation and to temperature effects on the Monod constant K(s), the immobilized-cell activity was less sensitive to temperature. The apparent activation energy for immobilized Ns. europaea was between 28.6 and 94.2 kJ mol(-1) and for immobilized Nb. agilis between 1.4 and 72.9 kJ mol(-1), depending on the oxygen concentration and temperature. (c) 1995 John Wiley & Sons, Inc.     

Influence of Yucca shidigera extract on ruminal ammonia concentrations and ruminal microorganisms.

An extract of the desert plant Yucca shidigera was assessed for its possible benefit in ruminal fermentation. The extract bound ammonia in aqueous solution when concentrations of ammonia were low (up to 0.4 mM) and when the extract was added at a high concentration to the sample (20%, vol/vol). The apparent ammonia-binding capability was retained after autoclaving and was decreased slightly following dialysis. Acid-precipitated extract was inactive. No evidence of substantial ammonia binding was found at higher ammonia concentrations (up to 30 mM). When Y. shidigera extract (1%, vol/vol) was added to strained rumen fluid in vitro, a small (6%) but significant (P < 0.05) decrease in ammonia concentration occurred, apparently because of decreased proteolysis. Inclusion of Y. shidigera extract (1%, vol/vol) in the growth medium of the rumen bacterium Streptococcus bovis ES1 extended its lag phase, while growth of Butyrivibrio fibrisolvens SH13 was abolished. The growth of Prevotella (Bacteroides) ruminicola B(1)4 was stimulated, and that of Selenomonas ruminantium Z108 was unaffected. Protozoal activity, as measured by the breakdown of 14C-leucine-labelled S. ruminantium in rumen fluid incubated in vitro, was abolished by the addition of 1% extract. The antimicrobial activities were unaffected by precipitating tannins with polyvinylpyrrolidone, but a butanol extract, containing the saponin fraction, retained its antibacterial and antiprotozoal effects. Saponins from other sources were less effective against protozoa than Y. shidigera saponins. Y. shidigera extract, therefore, appears unlikely to influence ammonia concentration in the rumen directly, but its saponins have antimicrobial properties, particularly in suppressing ciliate protozoa, which may prove beneficial to ruminal fermentation and may lead indirectly to lower ruminal ammonia concentrations.     

Conversion of acetohydroxamate and hydroxylamine to nitrite by intestinal microorganisms

Summary We have investigated the ability of intestinal microorganisms from the rat, guinea pig and man to carry out heterotrophic nitrification. We have shown that some intestinal isolates can oxidize acetohydroxamate and hydroxylamine to nitrite. Moreover, one of the isolates, Pseudomonas aeruginosa, exhibited the greatest nitrifying activity reported in the literature.This is correspondence No. 3967 from the Department of Nutrition and Food Science, Massachusetts Institute of Technology     

Effects of low concentrations of tetradotoxin on rat trigeminal ganglion neurons

Voltage clamping and intracellular perfusion methods were used to investigate ionic currents produced by depolarizing shifts of –120 mV from holding potential during experiments on neurons isolated from the trigeminial ganglion of one-month-old rats. It was found that tetradotoxin at low (external) concentrations of 10^–12–10¹⁰ M produced an increase in the amplitude and alternations in the kinetics of inward ionic currents. Similar effects were observed in 8 test cells out of 29. The extent to which the increase in the amplitude of inward ionic currents depended on concentration level could be described by Langmuir's isotherm, with a dissociation constant of the order of 5·10^–12 M. No such tetrodotoxin effects were observed when chloride ions were replaced by a non-penetrating anion in the intracellular solution. It is suggested that tetrodotoxin-sensitive channels exist in the neuronal membrane of the rat trigeminal ganglion, letting through chloride ions during depolarization of the membrane.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 18, No. 6, pp. 723–729, November–December, 1986.     

Effects of low concentrations of cetyltrimethylammonium bromide on diluted bovine spermatozoa

Cetyltrimethylammonium bromide (CTAB) at a concentration of 10 mg/l in a citrate buffer partially protected sperm against the effects of cold shock treatment. CTAB concentrations of 10 and 20 mg/l also increased in vitro sperm livability when semen was diluted in Caprogen and incubated at 37 degrees C (50 h v. 60 and 57 h). Concentrations of CTAB exceeding 50 mg/l reduced in vitro sperm livability. The addition of catalase (4.5 mg/l) to Caprogen produced greater increases in in vitro sperm livability (50 h v. 110 h), but did not eliminate the toxic effect of the higher CTAB concentrations. The addition of CTAB (10 mg/l) to the Caprogen-catalase diluent significantly increased the non-return rate of the diluted semen in only one of four large-scale field trials and did not alter non-return rates with deep-frozen semen.     

Effects of dissolved organic carbon and second substrates on the biodegradation of organic compounds at low concentrations.

Pseudomonas acidovorans and Pseudomonas sp. strain ANL but not Salmonella typhimurium grew in an inorganic salts solution. The growth of P. acidovorans in this solution was not enhanced by the addition of 2.0 micrograms of phenol per liter, but the phenol was mineralized. Mineralization of 2.0 micrograms of phenol per liter by P. acidovorans was delayed 16 h by 70 micrograms of acetate per liter, and the delay was lengthened by increasing acetate concentrations, whereas phenol and acetate were utilized simultaneously at concentrations of 2.0 and 13 micrograms/liter, respectively. Growth of Pseudomonas sp. in the inorganic salts solution was not affected by the addition of 3.0 micrograms each of glucose and aniline per liter, nor was mineralization of the two compounds detected during the initial period of growth. However, mineralization of both substrates by this organism occurred simultaneously during the latter phases of growth and after growth had ended at the expense of the uncharacterized dissolved organic compounds in the salts solution. In contrast, when Pseudomonas sp. was grown in the salts solution supplemented with 300 micrograms each of glucose and aniline, the sugar was mineralized first, and aniline was mineralized only after much of the glucose carbon was converted to CO2. S. typhimurium failed to multiply in the salts solution with 1.0 micrograms of glucose per liter. It grew slightly but mineralized little of the sugar at 5.0 micrograms/liter, but its population density rose at 10 micrograms of glucose per liter or higher. The hexose could be mineralized at 0.5 micrograms/liter, however, if the solution contained 5.0 mg of arabinose per liter.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of nitrite and ammonium on methane-dependent denitrification

For effective application of methane-dependent denitrification (MDD) in the treatment of wastewater containing NO(2)(-) or NH(4)(+), the effect of these inorganic nitrogen compounds on MDD activity needs to be clarified. The MDD activity of sludge acclimatized with CH(4) and O(2) was determined with mineral media of different nitrogen-compound compositions in the presence of 0.21 atm CH(4) and 0.20 atm O(2). Incubations with media containing only NO(2)(-) or two of the three inorganic nitrogen compounds (NO(3)(-)+NO(2)(-), NO(2)(-)+NH(4)(+) or NH(4)(+)+NO(3)(-)) resulted in MDD activity equal to or higher than that with media containing only NO(3)(-). However, there was no MDD activity in media containing NO(2)(-) at 10 degrees C, probably because of serious inhibition of NO(2)(-) on methane oxidation. MDD occurred in media containing only NH(4)(+), although the total nitrogen removal efficiency was very low. These results show that NO(2)(-) and NH(4)(+), in the presence of NO(x)(-), do not inhibit but rather promote MDD. Consequently, NH(4)(+) does not need to be completely oxidized to NO(3)(-) in the nitrification reactor before MDD. However, under psychrophilic conditions, NO(2)(-) seriously inhibited MDD. Therefore, the nitrification reactor must not discharge effluent containing NO(2)(-) under psychrophilic conditions.     

Effects of long-term treatment with acetylene on nitrogen-fixing microorganisms.

Long periods of experimental incubation with acetylene led to a multifold enhancement of acetylene-reducing activity in Anabaena cylindrica, Anabaenopsis circularis, Rhodospirillum rubrum, and Azotobacter vinelandii. Rates of acetylene reduction showed a gradual increase and reached a peak after 2 to 6 h of continuous incubation under acetylene. Thereafter, enzyme activity rapidly declined. A similar enhancement of ethylene production was observed when pretreatment with acetylene was interrupted periodically by a brief exposure to ambient (or oxygen-free) atmosphere without acetylene although the decline of acetylene-reducing activity was less rapid. Pretreatment with acetylene depressed photosynthetic 14CO2 fixation and 15N2 incorporation in Anabaena cylindrica. It is concluded that assessments based on long-term experimental incubation with acetylene may grossly overestimate the actual quantities of fixed nitrogen in the field.     

Effects of low concentrations of ethanol on the embryonic development of Bufo arenarum

The effects of low concentrations of ethanol on embryos of Bufo arenarum were studied. Embryos maintained continuously (from stage 3 on) in 0.84-3.34 microM ethanol showed concentration dependent effects: delay in the development rate and on eclosion, loss of equilibrium, arrhythmic contractions, swimming in atypical positions and high death rate. At lower concentrations the anomalies were concentration independent. Embryos treated continuously with 0.002 and 0.21 microM ethanol until stages 19, 20 and 21 showed an important and selective increase in their Na content. When the embryos were incubated discontinuously in 0.002 and 0.21 microM ethanol, from stage 3 to stages 12-13 and then transferred to Holtfreter solution, only a few of the above mentioned anomalies were observed; they were transient and the embryos recovered rapidly. Treated embryos did not exhibit ultrastructural changes in their ectodermal cells.     

Effects of long-term treatment with acetylene on nitrogen-fixing microorganisms.

Long periods of experimental incubation with acetylene led to a multifold enhancement of acetylene-reducing activity in Anabaena cylindrica, Anabaenopsis circularis, Rhodospirillum rubrum, and Azotobacter vinelandii. Rates of acetylene reduction showed a gradual increase and reached a peak after 2 to 6 h of continuous incubation under acetylene. Thereafter, enzyme activity rapidly declined. A similar enhancement of ethylene production was observed when pretreatment with acetylene was interrupted periodically by a brief exposure to ambient (or oxygen-free) atmosphere without acetylene although the decline of acetylene-reducing activity was less rapid. Pretreatment with acetylene depressed photosynthetic 14CO2 fixation and 15N2 incorporation in Anabaena cylindrica. It is concluded that assessments based on long-term experimental incubation with acetylene may grossly overestimate the actual quantities of fixed nitrogen in the field.     

Effects of extremely low concentrations of hormones on the insulin binding of Tetrahymena

FITC-insulin binding to previously hormone-treated Tetrahymena was studied by flow cytometry and confocal microscopy. Hormones produced by Tetrahymena were chosen for study and the hormone concentrations were administered between 10(-6) and 10(-21)M for 30 min. Endorphin, serotonin and insulin significantly reduced the hormone binding however histamine did not influence it at all. Endorphin, serotonin and insulin were significantly effective down to 10(-18)M and the effect of insulin and endorphin suggest a similar mechanism. The results call attention to the efficacy of very low hormone concentrations, which can influence the hormone content (earlier experiments) and receptor binding capacity (present study) of a unicellular organism. This seems to be very important, as in wild (natural) conditions the dilution of signaling materials secreted by a water-living protozoan is very high. In addition, the results point to the selectivity of response, as not all of the hormones that deeply influence other physiological indices (e.g. histamine) have an effect on insulin content or insulin receptors.     

Effects of denaturants at low concentrations on the reversible denaturation of staphylococcal nuclease

Three very unstable mutant forms of staphylococcal nuclease were used to quantitate the change in the apparent equilibrium constant for reversible denaturation (Kapp) as a function of denaturant concentration for a variety of different denaturing solutes. The value of this equilibrium constant in the absence of denaturant (Kapp,0) was determined by renaturation of the mutant proteins with a combination of glycerol and calcium ion, the latter of which binds at the active site in the native conformation. Because Kapp,0 fell in the easily measurable range between 0.1 and 1, the change in Kapp, and thus the change in free energy (delta Gapp), at very low concentrations of denaturants could be accurately measured. With guanidine hydrochloride (GuHCl), the rate of change of the apparent free energy of denaturation with respect to denaturant concentration (d(delta Gapp)/dCGuHCl or mGuHCl) was found to be remarkably constant down to zero denaturant concentration, even though this value was different for each of the three proteins. Unlike GuHCl, urea exhibited a slightly reduced value of d delta Gapp/dCurea at low concentrations. Results with a number of thiocyanate, perchlorate, and iodide salts confirmed that the Hofmeister series holds for concentrations below 0.1 M; that is, with regard to efficacy as a denaturant SCN- greater than ClO4- greater than I- and Li+,NH4+ greater than Na+,K+. However, all of the chaotropic salts analyzed exhibited markedly increased values of d(delta Gapp)/dCsalt at concentrations below 0.2 M. One possible explanation for these large deviations from a linear relationship between delta Gapp and salt concentration is that weak binding or adsorption of chaotropic anions is occurring at a saturable number of sites in hydrophobic regions of the denatured state.     

Effects of plutonium on soil microorganisms

As a first phase in an investigation of the role of the soil microflora in Pu complex formation and solubilization in soil, the effects of Pu concentration, form, and specific activity on microbial types, colony-forming units, and CO(2) evolution rate were determined in soils amended with C and N sources to optimize microbial activity. The effects of Pu differed with organism type and incubation time. After 30 days of incubation, aerobic sporeforming and anaerobic bacteria were significantly affected by soil Pu levels as low as 1 mug/g when Pu was added as the hydrolyzable Pu(NO(3))(4) (solubility, <0.1% in soil). Other classes of organisms, except the fungi, were significantly affected at soil Pu levels of 10 mug/g. Fungi were affected only at soil Pu levels of 180 mug/g. Soil CO(2) evolution rate and total accumulated CO(2) were affected by Pu only at the 180 mug/g level. Because of the possible role of resistant organisms in complex formation, the mechanisms of effects of Pu on the soil fungi were further evaluated. The effect of Pu on soil fungal colony-forming units was a function of Pu solubility in soil and Pu specific activity. When Pu was added in a soluble, complexed form [Pu(2)(diethylenetriaminepentaacetate)(3)], effects occurred at Pu levels of 1 mug/g and persisted for at least 95 days. Toxicity was due primarily to radiation effects rather than to chemical effects, suggesting that, at least in the case of the fungi, formation of Pu complexes would result primarily from ligands associated with normal (in contrast to chemically-induced) biochemical pathways.