Microorganisms degrading phenolic compounds play an important role in soil carbon cycling. The pcaH gene encoding a key ring-cleaving enzyme of the β -ketoadipate pathway was selected as a functional marker. Using a degenerate primer pair, pcaH fragments were cloned from two soils. The RFLP screening of 150 pcaH clones yielded 68 RFLP families. Comparison of 86 deduced amino acid sequences displayed 70 % identity to known PcaH sequences. Phylogenetic analysis results in two major groups mainly related to PcaH sequences from Actinobacteria and Proteobacteria phyla. This gene constitutes a suitable molecular marker to study the diversity of this functional group.

International audience | Microorganisms degrading phenolic compounds play an important role in soil carbon cycling. The pcaH gene encoding a key ring-cleaving enzyme of the β -ketoadipate pathway was selected as a functional marker. Using a degenerate primer pair, pcaH fragments were cloned from two soils. The RFLP screening of 150 pcaH clones yielded 68 RFLP families. Comparison of 86 deduced amino acid sequences displayed 70 % identity to known PcaH sequences. Phylogenetic analysis results in two major groups mainly related to PcaH sequences from Actinobacteria and Proteobacteria phyla. This gene constitutes a suitable molecular marker to study the diversity of this functional group.

International audience

Mercuric ions (Hg²⁺) and methylmercury are major, human-generated, toxic contaminants present in fish and our waterways. Bacteria provide a means of bioremediation by taking up these compounds and reducing them to volatile, non-toxic, elemental mercury (Hg°). Three types of mercury/methylmercury transporters have previously been identified: MerC, MerF and MerT. Each of these sets of homologues has distinct topologies. MerF proteins are characterized by a 2-transmembrane α-helical segment (TMS) topology; most MerTs have three TMSs, and MerCs have four TMSs. This report shows that MerT and MerF proteins are related by common descent and are similar in sequence throughout their first two TMSs. One of the MerF proteins is internally duplicated, generating a protein with four TMSs, while several MerT homologues bear a C-terminal extracytoplasmic Hg²⁺-binding MerP domain. MerPs are homologous to heavy metal-binding domains present in copper chaperone proteins, at the N-termini of mercuric reductases and in from one to six copies in heavy metal transporting P-type ATPases. Phylogenetic analyses reveal that mercuric ion transporters have been horizontally transferred with high frequency between bacteria. Some MerTs function with MerP receptors while others do not, and the MerP-dependent MerTs cluster separately from the MerP-independent MerTs on a phylogenetic tree. MerTs possessing a MerP appear to have co-evolved with their cognate receptors. Conserved sequence and motif analyses serve to define the mercuric transporter family fingerprints and allow prediction of specific subfunctions. This report provides the first detailed bioinformatic description of two apparently unrelated families of Hg²⁺ uptake transporters. We propose that all members of these two families function by a simple channel-type mechanism to allow influx of Hg²⁺ in response to the membrane potential in preparation for reduction and detoxification. This information should facilitate the exploitation of these transporters for purposes of microbial and phytobioremediation.

We tested the efficacy of matrix based fertilizer formulations (MBF) that reduce NH₄, total phosphorus (TP), total reactive phosphorus (TRP) and dissolved reactive phosphorus (DRP) in leachate. The MBF formulations cover a range of inorganic N and P in compounds that are relatively loosely bound (MBF1) to more moderately bound (MBF2) and more tightly bound compounds (MBF3) mixed with Al(SO₄)₃ H₂O and/or Fe₂(SO₄)₃ and with the high ionic exchange compounds starch, chitosan and lignin. Glomus interadicies, a species of arbuscular mycorrhizal fungal spores that will form mycorrhizae in high nutrient environments, was added to the MBF formulations to increase plant nutrient uptake. When N and P are released from the inorganic chemicals containing N and P the matrix based fertilizers likely bind these nutrients to the Al(SO₄)₃ H₂O and/or Fe₂(SO₄)₃ starch–chitosan–lignin matrix. We tested the efficacy of the MBFs to reduce N and P leaching compared to Osmocote® 14-14-14, a slow release fertilizer (SRF) in sand filled columns in a greenhouse study. SRF with and without Al and Fe leached 78–84% more NH₄, 58–78% more TP, 20–30% more TRP and 61–77% more than MBF formulations 1, 2, and 3 in a total of 2.0 liters of leachate after 71 days. The concentration and amount of NO₃ leached among SRF and MBF formulations 1 and 2 did not differ. The SRF treatment leached 34% less NO₃, than MBF3. Total plant weight did not differ among fertilizer treatments. Arbuscular mycorrhizal infection did not differ among plants receiving SRF and MBF formulations 1, 2 and 3. Although further greenhouse and field testing are called for, results of this initial investigation warrant further investigation of MBFs.

Investigation of nine herbaceous species collected around five polluters in northwestern Russia (nickel-copper smelters at Monchegorsk and Nikel, ore-roasting factory at Zapolyarnyy, aluminium smelter in Kandalaksha, and iron pellet plant at Kostomuksha) demonstrated that effects of pollution on plant growth were rarely significant in individual analyses. However, meta-analysis revealed decrease in plant size, in terms of height and leaf length; simultaneous increase in the number of leaves and flowers/inflorescences may compensate for this decline, thus the biomass of aboveground plant parts did not change. This result contrasts numerous experimental studies that generally demonstrate adverse effects of various pollutants on growth and reproduction of herbaceous plants, hinting that the effects detected in short-term experiments are of limited value for predicting performance of plant individuals surviving in polluted ecosystems. Changes in growth and reproduction of plants persisting under chronic pollution are minor presumably due to development of pollution tolerance and adaptation to altered environmental conditions.

Plant age affects its elemental uptake and biomass accumulation, which is important for the application of plants in phytoextraction. In this research, we evaluated the effects of plant age on arsenic accumulation by arsenic hyperaccumulator Pteris vittata after growing in an arsenic-contaminated soil for 8 weeks. The study used a completely randomized design consisting of four plant ages (2, 4, 10 and 16 months) with four replications each. While the fronds of the 2 month old plants contained 36% more arsenic than those of the 4 and 16 month old plants, they were lower in roots. After 8 weeks of growth, the final frond biomass increased by 39, 6.9, 2.0 and 1.1 times compared to the initial frond biomass, from youngest to oldest, respectively. Higher phosphorus and iron accumulation in the roots of older plants may have affected the plant's efficiency to bioconcentrate and transfer arsenic from the roots to the fronds. Greater metabolic activity and higher rate of biomass production lead to higher As accumulation and removal by young plants. This research demonstrated that the use of young plants can be an effective strategy to reduce the time to remediate an As-contaminated site.

Highly organic soils, and in particular ombrotrophic bogs, have been often used to reconstruct climate changes and heavy metal contaminations. Ombrotrophic peat bogs, in fact, are domed peatlands in which the surface layers are hydrologically isolated from the influence of local groundwaters and surface waters, and are supplied only by atmospheric depositions. In the present work, the attention of Authors has been focused on Pb, Cu, and Zn, coming mainly from anthropogenic activities, and ¹³⁷Cs, released mostly during the Chernobyl disaster. Practically, an undisturbed peat profile was cored in 2005 from a Swiss ombrotrophic bog and analysed using energy-dispersive miniprobe multielement analyzer X-ray fluorescence and Low Background γ-ray spectrometry in order to investigate and quantify the impact of human activities (e.g., industry, traffic, combustion of fossil fuels, “environmental disasters”) in causing Pb, Cu, Zn, and ¹³⁷Cs contaminations during the centuries. Obtained data show that highly organic soils in general, and ombrotrophic bogs in particular, reflect the anthropogenic inputs in heavy metal and radionuclide contaminations. In fact, these environments allowed to follow the depositional history of Pb, Cu, and Zn, both underlining a general increasing of their production since the Industrial Revolution, and remarking past single impacting events such as the introduction of leaded gasoline and of particular agricultural practices. Further, although ¹³⁷Cs showed a main peak corresponding to the Chernobyl disaster, confirming the role of bogs as archive of human activity, data revealed a certain mobility of this radionuclide along the profile. Thus, highly organic soils can be considered as both “witness” of the impact of human activity during centuries and indicator of the health of our planet.