Linking genetics, physiology and ecology: an interdisciplinary approach for advancing bioremediation

Chemotaxis Towards Aromatic Compounds: Insights from Comamonas testosteroni

Chemotaxis is an important physiological adaptation that allows many motile bacteria to orientate themselves for better niche adaptation. Chemotaxis is best understood in Escherichia coli. Other representative bacteria, such as Rhodobacter sphaeroides, Pseudomonas species, Helicobacter pylori, and Bacillus subtilis, also have been deeply studied and systemically summarized. These bacteria belong to α-, γ-, ε-Proteobacteria, or Firmicutes. However, β-Proteobacteria, of which many members have been identified as holding chemotactic pathways, lack a summary of chemotaxis. Comamonas testosteroni, belonging to β-Proteobacteria, grows with and chemotactically responds to a range of aromatic compounds. This paper summarizes the latest research on chemotaxis towards aromatic compounds, mainly from investigations of C. testosteroni and other Comamonas species.

Application of a long-lasting colloidal substrate with pH and hydrogen sulfide control capabilities to remediate TCE-contaminated groundwater

A long-lasting emulsified colloidal substrate (LECS) was developed for continuous carbon and nanoscale zero-valent iron (nZVI) release to remediate trichloroethylene (TCE)-contaminated groundwater under reductive dechlorinating conditions. The developed LECS contained nZVI, vegetable oil, surfactants (Simple Green™ and lecithin), molasses, lactate, and minerals. An emulsification study was performed to evaluate the globule droplet size and stability of LECS. The results show that a stable oil-in-water emulsion with uniformly small droplets (0.7 μm) was produced, which could continuously release the primary substrates. The emulsified solution could serve as the dispensing agent, and nZVI particles (with diameter 100-200 nm) were distributed in the emulsion evenly without aggregation. Microcosm results showed that the LECS caused a rapid increase in the total organic carbon concentration (up to 488 mg/L), and reductive dechlorination of TCE was significantly enhanced. Up to 99% of TCE (with initial concentration of 7.4 mg/L) was removed after 130 days of operation. Acidification was prevented by the production of hydroxide ion by the oxidation of nZVI. The formation of iron sulfide reduced the odor from produced hydrogen sulfide. Microbial analyses reveal that dechlorinating bacteria existed in soils, which might contribute to TCE dechlorination.

Enhanced biodegradation of petroleum hydrocarbons in the mycorrhizosphere of sub-boreal forest soils

Petroleum hydrocarbon (PHC) contamination is becoming more common in boreal forest soils. However, linkages between PHC biodegradation and microbial community dynamics in the mycorrhizosphere of boreal forest soils are poorly understood. Seedlings (lodgepole pine, paper birch, lingonberry) were established in reconstructed soil systems, consisting of an organic layer (mor humus, coarse woody debris, or previously oil-contaminated mor humus) overlying mineral (Ae, Bf) horizons. Light crude oil was applied to the soil surface after 4 months; systems were destructively sampled at 1 and 16 weeks following treatment. Soil concentrations of four PHC fractions were determined using acetone-hexane extraction followed by gas chromatography - flame ionization detection analysis. Genotypic profiles of root-associated bacterial communities were generated using length heterogeneity-PCR of 16S rDNA. Most plant-soil treatments showed significant loss in the smaller fraction PHCs indicating an inherent capacity for biodegradation. Concentrations of total PHCs declined significantly only in planted (pine-woody debris and birch-humus) systems (averaging 59% and 82% loss between 1 and 16 weeks respectively), reinforcing the importance of the mycorrhizosphere for enhancing microbial catabolism. Bacterial community structure was correlated more with mycorrhizosphere type and complexity than with PHC contamination. However, results suggest that communities in PHC-contaminated and pristine soils may become distinct over time.

Eubacterial diversity of activated biomass from a common effluent treatment plant

A common effluent treatment plant (CETP) is a biological wastewater treatment facility that receives wastewater from different industries. The activated biomass in the CETP survives on a wide range of chemicals with no fixed wastewater characteristics. We carried out a diversity analysis of this activated biomass using culture as well as culture-independent techniques. Using culture-based techniques, strains belonging to 26 different genera from the phyla Proteobacteria, Actinobacteria and Firmicutes were isolated. The gamma-proteobacteria was the best represented class, with 36.5% of the isolates. Bacterial diversity was also analyzed culture-independently by means of sequence determination of cloned 16S rRNA genes. Twenty-one different genera from the phyla Proteobacteria, Firmicutes, Planctomycetes and Bacteroidetes were identified. The total diversity of the activated biomass was composed of members of five known phyla, represented by 37 genera, with the Proteobacteria constituting the most abundant phylum detected. However, a very large fraction of the diversity represented a hitherto unidentified bacterial population. More than half (50.2%) of the 16S rDNA clones represented unidentified non-culturable bacteria, underlining the vast untapped diversity of CETP communities. Our results also indicate that both culture-based and culture-independent techniques should be combined to cover the microbial diversity of complex ecosystems.

Petroleum hydrocarbon contamination in boreal forest soils: a mycorrhizal ecosystems perspective

The importance of developing multi-disciplinary approaches to solving problems relating to anthropogenic pollution is now clearly appreciated by the scientific community, and this is especially evident in boreal ecosystems exposed to escalating threats of petroleum hydrocarbon (PHC) contamination through expanded natural resource extraction activities. This review aims to synthesize information regarding the fate and behaviour of PHCs in boreal forest soils in both ecological and sustainable management contexts. From this, we hope to evaluate potential management strategies, identify gaps in knowledge and guide future research. Our central premise is that mycorrhizal systems, the ubiquitous root symbiotic fungi and associated food-web communities, occupy the structural and functional interface between decomposition and primary production in northern forest ecosystems (i.e. underpin survival and productivity of the ecosystem as a whole), and, as such, are an appropriate focal point for such a synthesis. We provide pertinent basic information about mycorrhizas, followed by insights into the ecology of ecto- and ericoid mycorrhizal systems. Next, we review the fate and behaviour of PHCs in forest soils, with an emphasis on interactions with mycorrhizal fungi and associated bacteria. Finally, we summarize implications for ecosystem management. Although we have gained tremendous insights into understanding linkages between ecosystem functions and the various aspects of mycorrhizal diversity, very little is known regarding rhizosphere communities in PHC-contaminated soils. This makes it difficult to translate ecological knowledge into environmental management strategies. Further research is required to determine which fungal symbionts are likely to survive and compete in various ecosystems, whether certain fungal - plant associations gain in ecological importance following contamination events, and how PHC contamination may interfere with processes of nutrient acquisition and exchange and metabolic processes. Research is also needed to assess whether the metabolic capacity for intrinsic decomposition exists in these ecosystems, taking into account ecological variables such as presence of other organisms (and their involvement in syntrophic biodegradation), bioavailability and toxicity of mixtures of PHCs, and physical changes to the soil environment.