The role of microbial reductive dechlorination of TCE at a phytoremediation site

In April 1996, a phytoremediation field demonstration site at the Naval Air Station, Fort Worth, Texas, was developed to remediate shallow oxic ground water (< 3.7 m deep) contaminated with chlorinated ethenes. Microbial populations were sampled in February and June 1998. The populations under the newly planted cottonwood trees had not yet matured to an anaerobic community that could dechlorinate trichloroethene (TCE) to cis-1,2-dichloroethene (DCE); however, the microbial population under a mature (approximately 22-year-old) cottonwood tree about 30 m southwest of the plantings had a mature anaerobic population capable of dechlorinating TCE to DCE, and DCE to vinyl chloride (VC). Oxygen-free sediment incubations with contaminated groundwater also demonstrated that resident microorganisms were capable of the dechlorination of TCE to DCE. This suggests that a sufficient amount of organic material is present for microbial dechlorination in aquifer microniches where dissolved O2 concentrations are low. Phenol, benzoic acid, acetic acid, and a cyclic hydrocarbon, compounds consistent with the degradation of root exudates and complex aromatic compounds, were identified by gas chromatography/mass spectrometry (GC/MS) in sediment samples under the mature cottonwood tree. Elsewhere at the site, transpiration and degradation by the cottonwood trees appears to be responsible for loss of chlorinated ethenes.     

Microstructural characteristics of thin biofilms through optical and scanning electron microscopy

The combination of a conventional optical microscope with a specially designed glass flow cell was used to visualize in situ biofilms formed on opaque thin biomaterials through a simple non-invasive way (optical microscopy of thin biofilms, OMTB). Comparisons of OMTB with scanning electron microscopy (SEM) images were made. Thin metallic dental biomaterials were used as substrata. They were immersed in a synthetic saliva and in a modified Mitis–Salivarius medium inoculated with a consortium of oral microorganisms. To study the effect of bacterial motility, Pseudomonas fluorescens cultures were also used. The processes which give rise to the formation of the biofilm were monitored through OMTB. Biofilm microstructures like pores, water channels, streamers and chains of Streptococci, attached to the surface or floating in the viscous interfacial environment, could be distinguished. Thickness and roughness of the biofilms formed on thin substrata could also be evaluated. Distortions introduced by pretreatments carried out to prepare biological materials for SEM observations could be detected by comparing OMTB and SEM images. SEM images (obtained at high magnification but ex situ, not in real time and with pretreatment of the samples) and OMTB images (obtained in situ, without pretreatments, in real time but at low magnification) in combination provided complementary information to study biofilm processes on thin substrata.     

Application of 13C NMR to investigate the transformations and biodegradation of organic materials by wood- and soil-feeding termites, and a coprophagous litter-dwelling dipteran larva

Solid-state 13C nuclear magnetic resonance spectroscopy has been used to characterize the C in samples of the food (wood), gut contents and faeces from the wood-feeding termite, Microcerotermes parvus; soil in the guts and mound material from the soil-feeding termite, Thoracotermes macrothorax; and the food and faeces from the litter-feeding, coprophagous larvae of the dipteran fly, Bibio marci. Spectra from the wood-feeding termite indicated preferential loss of polysaccharide and accumulation of lignin with some modification to the O-aromatic-C and methoxyl-C (O-methyl-C) components during passage through the gut. Spectra for the soil-feeding termite indicated little change in the distribution of 13C between resonances following passage through the gut, except for some evidence of preferential polysaccharide loss. Interpretation of the spectra from these organisms was restricted by the relatively low C content of the soils and mound material, and by the large contribution to the NMR spectra from the gut tissue rather than the gut contents. Spectra for the litter-feeding dipteran larvae indicated preferential feeding on the polysaccharide-rich component of the litter and then overall loss of polysaccharide-C and accumulation of both aromatic-C and methoxyl-C in the gut. These changes were greater for the second passage than for the first passage through the gut, suggesting that principally mechanical and physical changes occurred initially and that chemical digestion was prevalent during the second passage.     

Effect of buffering on the phosphate-solubilizing ability of microorganisms

Native microflora present in the alkaline vertisols and two phosphate-solubilizing bacteria (PSB) isolated from soil using conventional screening media could not release phosphorus from alkaline Indian vertisol soils supplemented with carbon and nitrogen sources. The two PSBs could solubilize both rock phosphate and di-calcium phosphate in unbuffered media but failed to solubilize rock phosphate in buffered media. The organic acids secreted by these PSBs were 20–50 times less than that required to solubilize phosphorus from alkaline soil.     

The origin of prokaryotic life and molecular evolution

The origin of prokaryotic life is discussed with an emphasis on the self-assembly of early life in a microscale environment where ordered cellular structures and integrated functions evolved from disorder. Early molecular evolution may have been due to both molecular chaos and evolving molecular order.     

Stability of Recombinant Plasmids in Transgenic Microorganisms under Different Environmental Conditions

The copy number of R plasmids weakly depends on the selective pressure of the respective antibiotic but does depend on the physiology of the host species and the type of plasmids and cloned genes, whose expression leads to a further load on the biosynthetic apparatus of cells. The last factor is critical in the maintenance of recombinant plasmids in transgenic microorganisms.     

The influence of cyclic heating and cooling on <Emphasis Type="Italic">Escherichia coli</Emphasis> survival

Repeated heating and cooling in lethal (2–52°C) and nonlethal (2–37°C) temperature ranges resulted in cell death of Escherichia coli B/r and E. coli B_S?1 suspended in 0.01 M phosphate buffer, pH 7.0 at varying osmotic pressure, but not in cow’s milk. The lethal effect increased with the rate of heating and cooling and with increasing suspension media tonicity; it may be caused by the temperature destabilization of cellular osmotic homeostasis.     

Bioremediation Assessment of Hydrocarbon-Contaminated Soils from the High Arctic

The bioremediation potential of hydrocarbon-contaminated soils from the most northerly inhabited station in the world, Canadian Forces Station - Alert, was assessed. Microbial enumeration, by both viable plate counts and direct counts, combined with molecular analysis (polymerase chain reaction and colony hybridization) for hydrocarbon catabolic genes (alkB, ndoB, xylE), demonstrated the presence of significant numbers of cold-adapted hydrocarbon-degrading microorganisms. The degradative activity of these populations was assessed by mineralization of ¹⁴Clabeled hexadecane (C16) at 5°C in untreated and treated soils. Although very low rates of C16 mineralization were observed in the untreated soils, nutrient supplementation with a fertilizer markedly increased C16 mineralization. Highly active cold-adapted hydrocarbon-degrading consortia were prepared from soil slurries, and their degradative potentials were monitored by biomass measurements and mineralization activity. Bio augmentation of the contaminated soils with consortia containing the greatest percentages of degradative bacteria resulted in the shortest C16 mineralization acclimation period. However, treatment with the consortia plus fertilizer did not appreciably increase C16 mineralization or reduce total petroleum hydrocarbon concentrations to a greater extent than did the fertilizer treatment alone. These results indicate that the soils possessed sufficient numbers of cold-adapted degradative bacteria, and that fertilizer application alone was sufficient to obtain elevated levels of degradative activity at low ambient summer temperatures.     

Persistence of Bacillus thuringiensis parasporal crystal insecticidal activity in soil

Spores and parasporal crystals of a Bacillus thuringiensis var. aizawai (H-serotype 7), strain HD137, streptomycin-resistant mutant were added to acidic (pH 5.0) natural and autoclaved soil and incubated at ?0.10 MPa, 25°C. Populations of B. thuringiensis in both soil treatments showed exponential rates of mortality which were represented by linear regression, the loss of viability being greater in natural than autoclaved soil. In natural soil, parasporal crystal insecticidal activity was lost at a complex, nonexponential rate. The initial, rapid decrease of activity gradually slowed, and the level of activity stabilized at 10% of the original inoculum level after 250 days incubation, until the cessation of sampling at >2 years. In autoclaved soil no significant (P > 0.2) loss of parasporal crystal insecticidal activity was detected over the same period, which suggested that soil microorganisms were responsible for the loss of crystal insecticidal activity in the natural, nonsterilized soil. The rate of loss of crystal activity in natural soil correlated well with assay data reported in the literature using Galleria mellonella, which measures the combined activity of spore and crystal. In autoclaved soil correlation was poor, probably due to variability in the bioassay data.     

The Growth-promoting Effect of Beijerinckia mobilis and Clostridium sp. Cultures on Some Agricultural Crops

New strains of Beijerinckia mobilis and Clostridium sp. isolated from the pea rhizosphere were studied with respect to their promoting effect on the growth and development of some agricultural crops. Seed soaking in bacterial suspensions followed by the soil application of the suspensions or their application by means of foliar spraying was found to be the most efficient method of bacterization. The application of B. mobilis andClostridium sp. cultures in combination with mineral fertilizers increased the crop production by 1.5–2.5 times. The study of the population dynamics of B. mobilis by the method of genetic marking showed that this bacterium quickly colonized the rhizoplane of plants and, therefore, had characteristics of an r-strategist. At the same time, Clostridiumsp. was closer to K-strategists, since this bacterium slowly colonized the econiches studied. The introduction of the bacteria into soil did not affect the indigenous soil bacterial complex. The presence of Clostridium sp. slowed down the colonization of roots by the fungal mycelium. The possible mechanisms of the plant growth–promoting activity of B. mobilisand Clostridiumsp. are discussed.