Silvia Pascazio

Degradation of citrate promotes copper co-precipitation within aluminium-(hydr)oxides in calcareous soils

In this study, we provide experimental evidences that in calcareous soils microbial degradation/decomposition of citrate can promote Al-(hydr)oxide precipitation concurrently decreasing copper (Cu) solubility by a coprecipitation process. Citrate is an organic acid anion commonly released by roots to increase nutrient availability or to limit Al toxicity. However, under specific environmental conditions (i.e. high microbial activity of Al-citrate-degrading bacteria, alkaline pH), this organic acid may become ineffective in mobilizing Cu for the plant acquisition process. To demonstrate this, a calcareous soil and an artificial soil system have been treated with citrate solutions; then, changes in Al and Cu solubility and the formation of Cu-containing Al-(hydr)oxides were monitored. Both in experiments with the artificial soil and in those where the soil was inoculated with microbial strains, the formation of Cu-Al coprecipitates not only occurred but was also concurrent with the decrease of Cu and Al solubility. The role of bacteria in metal-citrate complex degradation has been assessed, and the 16S rDNA of bacteria related with these processes has been sequenced for genus identification. Bacteria belonging to Pseudomonas, Sphingomonas, Bradyrhizobium and Sphingopixis have been identified as possible candidates to degrade Al- and Cu-citrate complexes thus triggering the metal precipitation phenomena.

Biological and Biotechnological Evaluation of Carbon Dynamics in Field Experiments

Bacteria and fungi play a key role in promoting soil organic matter (SOM) turn over and consequent nutrient availability to plants uptake. During SOM degradation, they contribute to transform highly complex biomolecules to smaller compounds, which are either immobilized by soil microflora or self-associated in humified and microbially stable superstructures. These processes rapidly occur in the rhizosphere where soil adheres to plant roots and microbial populations are more abundant and active than in bulk soil. Despite the difficulties in determining the composition of soil microbial communities, their genetic and functional diversities are fundamental to maintain soil quality and productivity, even under environmental stress or alteration. Within the national MESCOSAGR project, we provided indications on the composition and diversity of bacterial communities in soils subjected to carbon sequestration treatments. Nucleic acids were extracted from rhizosphere and bulk soils, purified and amplified by polymerase chain reaction (PCR), targeting a conserved region of 16S rRNA gene. Amplicons were separated by denaturing gradient gel electrophoresis (DGGE) and cluster analysis of relative electrophoretic profiles was used to evaluate the diversity of bacteria communities in soils under different soil management practices. The PCR products have also been cloned and sequenced in order to identify and characterize the microbial groups and species which populated the experimental soils. Our results, relative to field trials of the first 2 years and three experimental sites, indicate that the application of different molecular approaches contribute to reach an advanced characterization of structure and diversity of soil bacteria, as well as an appraisal of their variation, as a consequence of specific soil management practices. In particular, it appears that only the amendments with mature compost had a significant effect on the soil microbial communities, while other soil treatments such as that with the iron–porphyrin biomimetic catalyst did not have any effect.