Mineralization of hexachlorocyclohexane in soil during solid-phase bioremediation

Soil containing hexachlorocyclohexane (HCH) was spiked with ¹⁴C--HCH and then subjected to bioremediation in bench-scale microcosms to determine the rate and extent of mineralization of the ¹⁴C-labeled HCH to ¹⁴CO₂. The soil was treated using two different DARAMEND amendments, D6386 and D6390. The amendments were previously found to enhance natural HCH bioremediation as determined by measuring the disappearance of parent compounds under either strictly oxic conditions (D6386), or cycled anoxic/oxic conditions (D6390). Within 80 days of the initiation of treatment, mineralization was observed in all of the strictly oxic microcosms. However, mineralization was negligible in the cycled anoxic/oxic microcosms throughout the 275-day study, even after cycling was ceased at 84 days and although significant removal (up to 51%) of indigenous -HCH (146 mg/kg) was detected by GC with electron capture detector. Of the amended, strictly oxic treatments, only one, in which 47% of the spiked ¹⁴C-HCH was recovered as ¹⁴CO₂, enhanced mineralization compared with an unamended treatment (in which 34% recovery was measured). Other oxic treatments involving higher amendment application rates or auxiliary carbon sources were inhibitory to mineralization. Thus, although HCH degradation occurs during the application of either oxic or cycled anoxic/oxic DARAMEND treatments, mineralization of -HCH may be inhibited depending on the amendment and treatment protocol.     

Non-Muscarinic- and Non-Adrenergic-Mediated Effects of Lindane on Phosphoinositide Hydrolysis in Rat Brain Cortex Slices

The influence of lindane upon phosphatidylinositol hydrolysis in rat brain cortex slices has been investigated using anion-exchange chromatography in order to separate the water-soluble inositol metabolites. Acetylcholine, noradrenaline, and lindane induce the accumulation of myo-[2-³H]inositol as the water-soluble inositol metabolites. However, the cholinergic muscarinic antagonist atropine inhibited the stimulatory response of carbachol, but practically unmodified the effect that lindane has on inositol phosphate production. Also, prazosin anti-₁ adrenoreceptors blocked noradrenaline-induced phosphoinositide hydrolysis, but had no effect on lindane-induced increase of inositol phosphate levels. The results suggest that lindane does not exert a general effect on the receptor-stimulated formation of inositol phosphates by both muscarinic and ₁-adrenergic agonists.     

Neurotoxicity of Lindane and Picrotoxin: Neurochemical and Electrophysiological Correlates in the Rat Hippocampus In Vivo

In the present study, we compared in vivo changes of extracellular amino acid levels and nucleotide derivatives to a single ip dose of lindane (10-60 mg/kg) and picrotoxin (5 mg/kg) in the hippocampus of halothane anaesthetized rat by microdialysis-coupled HPLC analysis. Brain activity was monitored by EEG. The effects of lindane and picrotoxin on EEG pattern of rats as well as on hippocampal amino acid and nucleotide status were studied in 0-50 min, 50-100 min and 100-150 min periods post-dosing. Significant decreases in Glu and Asp were found after picrotoxin treatment. After 50-100 min post-dosing, hippocampal hypoxanthine and inosine levels increased to both lindane (10 mg/kg) and picrotoxin whereas xanthine and uridine levels increased to picrotoxin, only. Lindane elicited a dose-dependent occurrence of negative spikes accompanied with rhythmic activity at 4-5 Hz. The picrotoxin-induced 4-5 Hz activity did not display negative sharp waves and was accompanied by 10 Hz oscillations.     

Effect of exposure to atmospheric pollution on microbial activity in soil

Summary Surface samples of a brown earth soil, showing signs of podzolization were transferred from an unpolluted woodland site and exposed to heavy atmospheric pollution for a period of one year. Although exposure resulted in a decrease in soil pH from 4.2 to 3.7, no significant changes in microbial numbers; nitrification rate; respiration rate; solubilization of insoluble phosphate; or the activity of a range of soil enzymes occurred. The rate of ammonification was, however, higher in the exposed than the control soil.Microbial activity in the unpolluted soil was not, therefore, substantially impaired by exposure to heavy atmospheric pollution, despite the fact that the pH of the soil was reduced.     

Effect of atrazine in combination with captan or thiram upon fungal and bacterial populations in the soil

Pesticides were added to soil at a rate of 10 mg/kg and then planted with corn, wheat, or bean seeds. Captan and thiram caused an initial decrease in the fungal populations but by 108 days the populations returned to levels found in untreated soils. The bacterial populations fluctuated inversely with the fungal populations. In soil planted with corn, atrazine had no effect on the microbial populations, however, in soil containing wheat and beans, populations of fungi and bacteria increased. Stimulation of the microbial populations in the atrazine-treated soils was attributed to the decay of the dead wheat and bean plants. Atrazine in combination with captan or thiram had neither synergistic nor antagonistic effects on the microbial populations. This study was supported by Public Health Service Research Grant No. CC 00284, from the National Communicable Disease Center, Atlanta, Georgia. This study was supported by Public Health Service Research Grant No. CC 00284, from the National Communicable Disease Center, Atlanta, Georgia.     

Adaptation of soil bacterial communities to prevailing pH in different soils

Abstract: The bacterial community response to pH was studied for 16 soils with pH(H₂O) ranging between 4 and 8 by measuring thymidine incorporation into bacteria extracted from the soil into a solution using homogenization-centrifugation. The pH of the bacterial solution was altered to six different values with dilute sulfuric acid or different buffers before measuring incorporation. The resulting pH response curve for thymidine incorporation was used to compare bacterial communities from the different soils. There was a correlation between optimum pH for thymidine incorporation and the soil pH(H₂O). Even bacterial communities from acid soils had optima corresponding to the soil pH, indicating that they were adapted to these conditions. Thymidine incorporation was also compared with leucine incorporation for some soils. The leucine to thymidine incorporation ratio was constant over the tested pH interval when incorporation values were adjusted for isotope dilution. A good correlation was found between the scores along the first component (explaining 80% of the variation) and soil pH ( r ² = 0.85), if principal component analysis of the pH response curves for thymidine incorporation was used. The pH response curves differed most for the extreme pH values used, and a linear relationship was found between the logarithm of the ratio of thymidine incorporation at pH 4.3 to incorporation at pH 8.2 and the soil pH ( r ² = 0.86). Thus, a simplified technique using only two pH values, when measuring the thymidine incorporation, could be used to compare the response to pH of bacterial communities.     

Effects of sieving, drying and rewetting upon soil bacterial community structure and respiration rates

Soil microcosm studies often require some form of soil homogenisation, such as sieving, to provide a representative sample. Frequently, soils are also homogenised following drying and are then rewetted, yet little research has been done to understand how these methods impact upon microbial communities. Here we compared the molecular diversity and functional responses of intact cores from a Scottish grassland soil with homogenised samples prepared by drying, sieving and rewetting or freshly sieving wet soils. Results showed that there was no significant difference in total soil CO₂-C efflux between the freshly sieved and intact core treatments, however, respiration was significantly higher in the dried and rewetted microcosms. Molecular fingerprinting (T-RFLP) of bacterial communities at two different time-points showed that both homogenisation methods significantly altered bacterial community structure with the largest differences being observed after drying and rewetting. Assessments of responsive taxa in each treatment showed that intact cores were dominated by Acidobacterial peaks whereas an increased relative abundance of Alphaproteobacterial terminal restriction fragments were apparent in both homogenised treatments. However, the shift in community structure was not as large in the freshly sieved soil. Our findings suggest that if soil homogenisation must be performed, then fresh sieving of wet soil is preferable to drying and rewetting in approximating the bacterial diversity and functioning of intact cores.     

林丹烟剂干扰下毛竹(Phyllostachys heterocycla cv.pubescens)林节肢动物群落的结构与组成

对林丹烟剂干扰下毛竹（Phyllostachys heterocycla cv.pubescens）林节肢动物群落结构与组成的系统定位观察与分析表明：长期使用林丹烟剂明显增加了群落主要物种（Pi≥0.05）的植食性种类及其优势度,显著降低群落总体的物种多样性,减少蜘蛛目、膜翅目、鞘翅目和双翅目或捕食性、寄生性和中性功能集团的物种数,削弱林冠层寄生性和捕食性物种在种类和数量上对植食性物种的制约潜能,引起叶部植食性害虫的暴发。因此,在毛竹害虫控制中应避免长期大量使用林丹烟剂。     

Survey of bacterial populations present in US‐produced linerboard with high recycle content

Aims: To survey paperboard products from 17 US mills for bacterial populations and for bacteria potentially harmful to human health. Methods and Results: Culturable aerobic bacteria were isolated from paperboard products using selective and nonselective medium. Resulting colonies from samples from three regions of the United States were identified using fatty acid methyl ester analysis. Percentages of bacteria species found were Bacillus megaterium (47), Bacillus licheniformis (15), Bacillus pumilus (12), Paenibacillus macerans (5), Paenibacillus pabuli (3), Bacillus subtilis (2), Bacillus cereus (2), Bacillus coagulans (1), Bacillus circulans (1), Bacillus brevis (1), Bacillus thuringiensis (1), Paenibacillus polymyxa (1), Cellulomonas turbata (1), Cellulomonas flavigena (1), unidentified Bacillus sp. (3) and unidentified bacteria (1). Conclusions: Recycled paperboard contained high populations of bacteria, and a positive correlation was found between recycle content and bacterial populations. Escherichia coli, Salmonella, Shigella or confirmed coliform bacteria were not found in any product. Significance and Impact of the Study: Populations of bacteria did not differ significantly from original counts over a 4‐month period of dry storage, indicating that bacteria persist in paperboard over long periods and may re‐enter the recycling process. The predominance of heat‐tolerant endospore‐forming bacteria explains the high bacteria counts found in paperboard made from recycled materials .     

Plasmids foster diversification and adaptation of bacterial populations in soil

It is increasingly being recognized that the transfer of conjugative plasmids across species boundaries plays a vital role in the adaptability of bacterial populations in soil. There are specific driving forces and constraints of plasmid transfer within bacterial communities in soils. Plasmid-mediated genetic variation allows bacteria to respond rapidly with adaptive responses to challenges such as irregular antibiotic or metal concentrations, or opportunities such as the utilization of xenobiotic compounds. Cultivation-independent detection and capture of plasmids from soil bacteria, and complete sequencing have provided new insights into the role and ecology of plasmids. Broad host range plasmids such as those belonging to IncP-1 transfer a wealth of accessory functions which are carried by similar plasmid backbones. Plasmids with a narrower host range can be more specifically adapted to particular species and often transfer genes which complement chromosomally encoded functions. Plasmids seem to be an ancient and successful strategy to ensure survival of a soil population in spatial and temporal heterogeneous conditions with various environmental stresses or opportunities that occur irregularly or as a novel challenge in soil.     

Effects of freeze-thaw stress on bacterial populations in soil microcosms

To test the effect of freezing on soil biota, isolated from the shortgrass prairie of northeastern Colorado, a series of experiments were performed using gnotobiotic soil microcosms.Pseudomonas paucimobilis was used to examine the effects of freezing on bacteria of different growth stages. Secondly, the effect of multiple freeze-thaw cycles was tested on an assemblage of bacterial species. Lastly, the effect of freezing on predator-prey interactions was studied usingP. paucimobilis and an amoebal predator,Acanthamoeba polyphaga. A temperature of ?9°C was not detrimental toP. paucimobilis at any growth stage. A single severe freeze-thaw cycle (?27°C to 23°C) resulted in 40–60% mortality ofP. paucimobilis and the mixed bacteria, although additional freezing events did not reduce the populations further. Multiple freeze-thaw cycles (?9°C to 23°C) gave 40–60% mortality ofP. paucimobilis and the mixed bacteria. Predator-prey population cycles were possibly desynchronized by freeze-thaw events.     

Multi-scale variability in tropical soil nutrients following land-cover change

The effects of land-cover change on soil properties have reached regional proportions in the southwestern Amazon, and can be detected in their patterns at the scale of hundreds of thousands of square kilometers. Spatial analysis of an extensive soil profile database revealed four nested spatial scales at which different patterns in soil properties occur: <3, <10, <68, and >68 km. The shortest scales account for the majority of the spatial variability in the biogeochemically important properties (phosphorus, nitrogen, organic carbon), while the longest scales explain the most for pedologic properties (pH, aluminum, percent clay and sand). The magnitude and sign of correlations among soil properties changed with scale, indicating major shifts in distribution and soil dynamics depending on the scale of observation and analysis. Precipitation, substrate composition, topography, and biological influences vary over large areas, leading to variable distribution of soil properties, and complicating the evaluation of the effect of deforestation on biogeochemical cycling. We modeled the relationships among scale-specific patterns in soil properties and the soil forming state factors to tease out the relative impact of changing land cover. Soil property short-scale variability corresponded with the distribution of land cover and terrain attributes, medium scale variation with geology and state soil map classifications, and long scale with geology and precipitation. The strength of these relationships may be partially attributable to the resolution of the maps used as proxies for the soil forming factors. Land-cover change has already left a discernable imprint on broad-scale soil nutrient patterns, although it is still not the dominant process.     

Pre-exposure to drought increases the resistance of tropical forest soil bacterial communities to extended drought

Global climate models project a decrease in the magnitude of precipitation in tropical regions. Changes in rainfall patterns have important implications for the moisture content and redox status of tropical soils, yet little is known about how these changes may affect microbial community structure. Specifically, does exposure to prior stress confer increased resistance to subsequent perturbation? Here we reduced the quantity of precipitation throughfall to tropical forest soils in the Luquillo Mountains, Puerto Rico. Treatments included newly established throughfall exclusion plots (de novo excluded), plots undergoing reduction for a second time (pre-excluded) and ambient control plots. Ten months of throughfall exclusion led to a small but statistically significant decline in soil water potential and bacterial populations clearly adapted to increased osmotic stress. Although the water potential decline was small and microbial biomass did not change, phylogenetic diversity in the de novo-excluded plots decreased by ∼40% compared with the control plots, yet pre-excluded plots showed no significant change. On the other hand, the relative abundances of bacterial taxa in both the de novo-excluded and pre-excluded plots changed significantly with throughfall exclusion compared with control plots. Changes in bacterial community structure could be explained by changes in soil pore water chemistry and suggested changes in soil redox. Soluble iron declined in treatment plots and was correlated with decreased soluble phosphorus concentrations, which may have significant implications for microbial productivity in these P-limited systems.     

The effects of soil horizons and faunal excrement on bacterial distribution in an upland grassland soil

The density and spatial location of bacteria were investigated within different horizons of an upland grassland soil before and after a liming treatment to increase the numbers of large soil fauna. Bacterial cells were located by image analysis of stained thin sections and densities calculated from these data. Excrement from macro- and meso-fauna was identified using micromorphology and the densities of bacteria on specific areas of excrement measured by image analysis. There were significant differences among horizons in the density of bacterial cells, with the minimum density found in the horizon with least evidence of earthworm activity, but no difference in density between the organic H and organo-mineral Ah horizons. Soil improvement by liming significantly increased bacterial densities in all three horizons, with the greatest increase found in the horizon with the smallest density before liming. There were no differences in bacterial density between areas dominated by excrement from earthworms and excrement from enchytraeids, although densities in both areas were significantly increased by liming. Variability in bacterial density at spatial scales of less than 1 mm was linked to the occurrence of excrement. Bacterial densities within areas of both types of excrement were significantly greater than those in the surrounding soil. However, the frequency distribution of the ratios of density in excrement to that in the soil was bimodal, with a majority of occurrences having a ratio near 1 and only some 20-30% having a much larger ratio. These variations can probably be explained by variations in the age of the excrement and its suitability as a substrate.     

The Pressurized Porous Surface Model: An improved tool to study bacterial behavior under a wide range of environmentally relevant matric potentials

To study bacterial behavior under varying hydration conditions similar to surface soil, we have developed a system called the Pressurized Porous Surface Model (PPSM). Thin liquid films created by imposing a matric potential of − 0.4 MPa impact gene expression and colony development in Pseudomonas putida.     

Comparison of two sympatric Pasteuria populations isolated from a tropical vertisol soil

An isolate of Pasteuria (designated PPMJ) recovered from the root-knot nematode Meloidogyne javanica, was characterized using host preference, spore morphometrics, and serology, and compared with another sympatric Pasteuria isolate (designated PPHC) collected from the cyst nematode, Heterodera cajani. PPMJ spores were larger (x 1.5) than the PPHC spores and had a mean diameter of 3.4 m after fixation for electron microscopy. The central body of PPMJ spores was about twice as big as the central body of PPHC spores. The host preference tests, based on spore attachment to the nematode cuticle, revealed that Meloidogyne incognita, M. javanica, M. hapla, Pratylenchus coffeae, and Pratylenchus sp. were hosts of PPMJ but not of PPHC. It was found that males of Radopholus similis were hosts of PPHC. Western blot analysis of spore extracts probed with a polyclonal antiserum raised against PPHC spores showed an antigenic ladder which had similarities to lipopolysaccharide; another antiserum revealed differences in the molecular weight of antigens of the different spore isolates. Population diversity can therefore be vastly altered by the maintenance and culture of the bacterium on a particular host. The implications of these results are discussed in relation to the use of Pasteuria as a biological control agent.K.G. Davies is with IACR-Rothamsted, Harpenden, Hertfordshire, AL5 2JQ, UK S.B. Sharma is with the International Crops Research Institute for the Semi-Aird Tropics (ICRISAT) Asia Center. Patancheru 502324, India.     

Further evidence for the regulation of bacterial populations in soil by protozoa

After the addition to soil of large numbers of a cowpea Rhizobium strain, the population declined steadily until the numbers reached about 10⁷/g, and the protozoa rose to about 10⁴/g. When indigenous protozoa were suppressed by the addition of actidione to the soil, the density of the test rhizobium did not fall initially, but its abundance declined to about 10⁷/g when actidione-resistant protozoa arose in significant numbers. The addition to actidione-treated soil of an antibiotic-resistant strain of Paramecium led to a rapid decrease in the population of the rhizobium, the density reaching essentially the same value as in soil receiving neither the drug nor the paramecia. The same changes occurred with Xanthomonas campestris as test prey except that its numbers fell to about 10⁵/g of soil. These data provide further evidence for the key role of protozoa in controlling the abundance of populations of certain bacteria introduced into soil.     

Analysis of bacterial populations in a grassland soil according to rates of development on solid media

Abstract The process of colony formation by bacteria from grassland soil sampled in April, July and September was simulated by a colony-forming curve (CFC). The CFC was a super-imposition of several component curves (cCFC) given theoretically by the first order reaction (FOR) model [3,6]. The pattern of FOR model curves was not influenced by the time of sampling and four cCFCs were always recognized during an incubation period of 160 h. It was considered that the CFC describes an inherent property of the bacterial population of the field. Bacterial isolates were obtained from colonies produced in each of four cCFCs on agar plates. Isolates corresponding to one cCFC were classified as one group. The bacterial isolates were characterized by morphological and physiological tests and subsequently clustered. Few oligotrophic bacteria were obtained among bacteria which produced visible colonies within 63 h of incubation time. On the other hand, approx. 50% of bacteria which produced v colonies after 63 h were oligotrophic bacteria. The time required for the appearance of the first colony, t _r of the FOR model, was very similar in the isolates belonging to one group. A close linear relationship was observed between t _r value and doubling time of isolates.