Toxicity of nano-scaled aluminum, silicon, titanium and zinc oxides to bacteria (Bacillus subtilis, Escherichia coli and Pseudomonas fluorescens) was examined and compared to that of their respective bulk (micro-scaled) counterparts. All nanoparticles but titanium oxide showed higher toxicity (at 20 mg/L) than their bulk counterparts. Toxicity of released metal ions was differentiated from that of the oxide particles. ZnO was the most toxic among the three nanoparticles, causing 100% mortality to the three tested bacteria. Al2O3 nanoparticles had a mortality rate of 57% to B. subtilis, 36% to E. coli, and 70% to P. fuorescens. SiO2 nanoparticles killed 40% of B. subtilis, 58% of E. coli, and 70% of P. fluorescens. TEM images showed attachment of nanoparticles to the bacteria, suggesting that the toxicity was affected by bacterial attachment. Bacterial responses to nanoparticles were different from their bulk counterparts; hence nanoparticle toxicity mechanisms need to be studied thoroughly. Oxide nanoparticles show higher toxicity than their bulk counterparts.

Bacteria from this soil were cultured in mineral salt solution supplemented with mesotrione as sole source of carbon for the isolation of mesotrione-degrading bacteria. The bacterial community structure of the enrichment cultures was analyzed by temporal temperature gradient gel electrophoresis (TTGE). The TTGE fingerprints revealed that mesotrione had an impact on bacterial community structure only at its highest concentrations and showed mesotrione-sensitive and mesotrione-adapted strains. Two adapted strains, identified as Bacillus sp. and Arthrobacter sp., were isolated by colony hybridization methods. Biodegradation assays showed that only the Bacillus sp. strain was able to completely and rapidly biotransform mesotrione. Among several metabolites formed, 2-amino-4-methylsulfonylbenzoic acid (AMBA) accumulated in the medium. Although sulcotrione has a chemical structure closely resembling that of mesotrione, the isolates were unable to degrade it. A Bacillus sp. strain isolated from soil was able to completely and rapidly biotransform the triketone herbicide mesotrione.

Antibiotics are among the most successful drugs used for human therapy. However, since they can challenge microbial populations, they must be considered as important pollutants as well. Besides being used for human therapy, antibiotics are extensively used for animal farming and for agricultural purposes. Residues from human environments and from farms may contain antibiotics and antibiotic resistance genes that can contaminate natural environments. The clearest consequence of antibiotic release in natural environments is the selection of resistant bacteria. The same resistance genes found at clinical settings are currently disseminated among pristine ecosystems without any record of antibiotic contamination. Nevertheless, the effect of antibiotics on the biosphere is wider than this and can impact the structure and activity of environmental microbiota. Along the article, we review the impact that pollution by antibiotics or by antibiotic resistance genes may have for both human health and for the evolution of environmental microbial populations. The article reviews the current knowledge on the effects that pollution by antibiotics and antibiotic resistance genes may have for the microbiosphere.

For phytoremediation of organic contaminants, plants have to host an efficiently degrading microflora. To assess the role of endophytes in alkane degradation, Italian ryegrass was grown in sterile soil with 0, 1 or 2% diesel and inoculated either with an alkane degrading bacterial strain originally derived from the rhizosphere of Italian ryegrass or with an endophyte. We studied plant colonization of these strains as well as the abundance and expression of alkane monooxygenase (alkB) genes in the rhizosphere, shoot and root interior. Results showed that the endophyte strain better colonized the plant, particularly the plant interior, and also showed higher expression of alkB genes suggesting a more efficient degradation of the pollutant. Furthermore, plants inoculated with the endophyte were better able to grow in the presence of diesel. The rhizosphere strain colonized primarily the rhizosphere and showed low alkB gene expression in the plant interior. Bacterial alkane degradation genes are expressed in the rhizosphere and in the plant interior.

The bracket-like polypore fungus, Ganoderma australe, was selected for its potential to degrade lindane in liquid agitated sterile cultures. An orthogonal central composite design based on response surface methodology was used to find the optimum biodegradation and biosorption conditions of this pesticide and the growth conditions of the fungus. The factors tested include nitrogen content, initial concentration of lindane, incubation time, and temperature. The optimization parameters investigated were fungus biomass, fungus growth rate, final pH, specific biodegradation, specific biosorption, specific biodegradation rate, biodegraded to biosorbed ratio. The results of the experiments were statistically analyzed and the significance and effect of each factor on responses was assessed. The optimum (maximum) lindane biodegradation (3.11 mg biodegraded lindane per gram biomass) was obtained with nitrogen content of 1.28 g/L, lindane concentration of 7.0 ppm, temperature of 18.0°C, and 5 days of cultivation time.

Fecal pollution from human and natural sources enters soil or watercourses, mixes, then reemerges as a nuisance of unknown origin. Before remediation is attempted, the sources and identities of pollution must be identified. Previous microbial source tracking studies have relied on traditional methods of microbiology such as selective media and biochemical characteristics to quantify fecal bacteria in water samples. This is successful when single sources are responsible for pollution. However, when multiple sources are present, numbers must be subdivided into categories of pollution to define relative importance and select appropriate methods of remediation which are very different for examples such as humans and avifauna pollution. Rather than depending on a single method, we recommend a tiered approach which takes advantage of ecological parameters and conventional microbiology to provide context for more precise DNA data and related statistics.

Rhizobacteria possess a wide variety of qualities governing their pollutant-catabolic and rhizospheric competences. We investigated how the abilities to degrade phenanthrene and other polycyclic aromatic hydrocarbons (PAHs), to synthesize surfactants and the phytohormone indole-3-acetic acid (IAA), to be motile, and to perform chemotaxis toward phenanthrene and some potential root-exudate components were manifested in rhizobacteria isolated from oil-polluted sites. We observed that most of the examined rhizobacteria had the abilities under consideration and that in some strains, these were strongly affected by the bacterial environment. Only one strain--Sinorhizobium meliloti P221--exhibited increased PAH-degrading, surfactant-producing, and IAA-synthesizing activities, as well as distinct behavioral responses. We conclude that S. meliloti P221 can be used as a model to assess the contributions of all these activities to plant-inoculation-induced reduction in the soil PAH contents. This strain also may be useful for phytoremediation applications.

Naphthenic acids (NAs) are a complex group of naturally occurring oil sands constituents that constitute a significant portion of the dissolved organic carbon (DOC) pool available for microbial degradation in the process-related waste water associated with oil sands mine sites. One approach to understanding the biological fate of oil sands process-derived carbon and nitrogen in aquatic reclamation of the mine sites involves the use of stable isotope analyses. However, for stable isotope analyses to be useful in such field-based assessments, there is a need to determine how microbial degradation of a complex mixture of NAs might change the stable isotope values (δ ¹³C, δ ¹⁵N). In batch cultures and semi-continuous laboratory microcosms, utilization of a commercial mixture of NAs by oil sands-derived microbial cultures resulted in microbial biomass that was similar or slightly ¹³C enriched (1.4[per thousand] to 3.0[per thousand]) relative to the DOC source, depending on the length of incubation. Utilization of a NA-containing extract of oil sands processed water resulted in greater ¹³C enrichment of microbial biomass (8.5[per thousand]) relative to the DOC source. Overall, the δ ¹³C of the DOC comprised of complex mixtures of NAs showed minimal change (-0.5[per thousand] to -0.1[per thousand]) during the incubation period whereas the δ ¹³C of the dissolved inorganic carbon (DIC) was more variable (-5.0[per thousand] to +5.4[per thousand]). In tests where the concentration of available nitrogen was increased, the final biomass values were ¹⁵N enriched (3.8[per thousand] to 8.4[per thousand]) relative to the initial biomass. The isotope trends established in this study should enhance our ability to interpret field-based data from sites with hydrocarbon contamination, particularly in terms of carbon source utilization and ¹⁵N enrichment.

The effect of exogenously added sodium dodecylbenzenesulphonate (SDBS) surfactant on biodegradation of a mixture of straight-chain aliphatic hydrocarbons (dodecane and hexadecane) and resulting cell surface hydrophobicity changes of Candida maltosa EH 15 were investigated. Results indicated that up to 75 mg/L SDBS improves the biodegradation potential of examined yeast. A decrease in hydrophobicity was observed when SDBS was supplemented in higher concentrations, having strong impact on biodegradation rates. Phase distribution of surfactant molecules was investigated using methylene blue active substances method (MBAS), accompanied by surface and interfacial tension measurements. Studies showed that portion of SDBS molecules adsorbed on cell surface may play significant role in interaction between anionic surfactant and yeast cells, having influence on biodegradation rates.