Restoration of a Mediterranean forest after a fire: bioremediation and rhizoremediation field-scale trial.

Forest fires pose a serious threat to countries in the Mediterranean basin, often razing large areas of land each year. After fires, soils are more likely to erode and resilience is inhibited in part by the toxic aromatic hydrocarbons produced during the combustion of cellulose and lignins. In this study, we explored the use of bioremediation and rhizoremediation techniques for soil restoration in a field-scale trial in a protected Mediterranean ecosystem after a controlled fire. Our bioremediation strategy combined the use of Pseudomonas putida strains, indigenous culturable microbes and annual grasses. After 8 months of monitoring soil quality parameters, including the removal of monoaromatic and polycyclic aromatic hydrocarbons as well as vegetation cover, we found that the site had returned to pre-fire status. Microbial population analysis revealed that fires induced changes in the indigenous microbiota and that rhizoremediation favours the recovery of soil microbiota in time. The results obtained in this study indicate that the rhizoremediation strategy could be presented as a viable and cost-effective alternative for the treatment of ecosystems affected by fires.

Synergic role of the two ars operons in arsenic tolerance in Pseudomonas putida KT2440.

The chromosome of Pseudomonas putida KT2440 carries two clusters of genes, denoted ars1 and ars2, that are annotated as putative arsenic resistance operons. In this work, we present evidence that both operons encode functional arsenic-response regulatory genes as well as arsenic extrusion systems that confer resistance to both arsenite [As(III)] and arsenate [As(V)]. Transcriptional fusions of P(ars1) and P(ars2) to lacZ revealed that expression of both operons was induced by arsenite and arsenate. We generated single mutants in ars1 and ars2, which showed lower resistance to arsenic than the wild-type strain. A double ars1/ars2 was found to be highly sensitive to arsenic. Minimum inhibitory concentrations (MICs) for single mutants decreased two- to fourfold with respect to the parental strain, while in the double mutant the MIC decreased 128-fold for arsenite and 32-fold for arsenate. Bioinformatic analysis revealed that the ars2 resistance operon is part of the core genome of P. putida, while the ars1 operon appears to only occur in the KT2440 strain, suggesting that ars1 was acquired by horizontal gene transfer. The presence of ars1 in KT2440 may explain why it exhibits higher resistance to arsenic than other P. putida strains, which bear only the ars2 operon.

Analysis of solvent tolerance in Pseudomonas putida DOT-T1E based on its genome sequence and a collection of mutants.

Pseudomonas putida strains are prevalent in a variety of pristine and polluted environments. The genome of the solvent-tolerant P. putida strain DOT-T1E which thrives in the presence of high concentrations of monoaromatic hydrocarbons, contains a circular 6.3 Mbp chromosome and a 133 kbp plasmid. Omics information has been used to identify the genes and proteins involved in solvent tolerance in this bacterium. This strain uses a multifactorial response that involves fine-tuning of lipid fluidity, activation of a general stress-response system, enhanced energy generation, and induction of specific efflux pumps that extrude solvents to the medium. Local and global transcriptional regulators participate in a complex network of metabolic functions, acting as the decision makers in the response to solvents.

Laboratory research aimed at closing the gaps in microbial bioremediation.

The industrial revolution, the first agricultural 'green revolution', and the development of antibiotics and therapeutic chemicals have brought significant and undeniable benefits to the human race. However, these advances demand high levels of energy, exploit natural resources and create large amounts of waste that creates an environmental burden for our planet. The pollution rate and character of many of the pollutants results in a rapid deterioration of the environment. Bioremediation functions to isolate and select microorganisms that operate under aerobic and anoxic conditions to remove these harmful pollutants. Current 'omics' technologies allow the exploitation of the catabolic potential of microbes without the need to cultivate them. Synthetic microbiology builds new catabolic pathways to remove recalcitrant pollutants from the environment.