Investigating the Concomitant Removal of Hydrocarbons and Heavy Metals by highly adapted Bacillus and Pseudomonas strains

This study investigates the concomitant removal of hydrocarbons and heavy metals by highly adapted Bacillus and Pseudomonas strains. In regions characterized by harsh conditions such as Qatar, the weathering processes would affect the content, status, and distribution of these contaminants. It was shown in the weathered soil from Dukhan oil wastes dumpsite that 14 heavy metals exceeded the EPA limits. Moreover, it was demonstrated that soil organics did not affect the distribution of the metals in the soil. However, most of the heavy metals were strongly bonded to the residual and the iron-manganese oxide fractions. Eighteen bacterial strains isolated from highly weathered oily soils were able to grow with heavy metal concentrations up to 3 mM and above for some. Seven selected strains (4 Bacillus and 3 Pseudomonas) showed the ability to remove almost 60 to 70% of most of the heavy metals when used at 1 mM. Moreover, they removed up to 75% of the diesel range organics. These results are of interest for selecting bacterial strains, which can overcome the toxicity of hydrocarbons and heavy metals and remove them concomitantly.

Enzymatic and microbial activities as influenced by tillage and fertilization in a semi-arid Mediterranean agroecosystem

<p>Soil enzymes respond rapidly to changes in soil managements, and therefore are used as early and sensitive indicators of alteration in soil properties induced by tillage and additions of fertilizers. The aim of this work was to compare the effects of different tillage (no, minimum, and conventional tillage), fertilization and soil depth (0-30, 30-60 and 60- 90 cm) on the microbial biomass, enzyme activity and their relationship with soil nutrients in a semiarid Mediterranean agro-ecosystem. Growing and total microbial biomass decreased with depth together with the activities of β-glucosidase and N-acetyl-β-glucosaminidase presumably because of the reduced carbon and oxygen content in the deeper layers of soils. The fertilization stimulated fast-growing microorganisms with low affinity of enzyme systems to substrate, enhanced the growing microbial biomass and facilitated the turnover rate of soil organics. Under no tillage, all enzymes showed higher potential activity in top layers of fertilized plots as compared with non-fertilized ones. The minimum tillage practice increased the growing microbial biomass, and stimulated N- and P-acquiring enzymes due to  increased nutrients limitation. Parameters of microbial growth and enzyme kinetics are suitable indicators of microbial activity in semiarid Mediterranean agroecosystems.</p>

Functional traits of hydrolytic enzymes and visualized enzymatic activity in the rhizosphere gradients of Zea mays L.

<p>Alive plants and soil microorganisms are the influential sources of extracellular enzymes facilitating decomposition of polymeric organic compounds. Enzyme activities are especially intensive and spatially heterogeneous in the rhizosphere, where microorganisms are stimulated by rhizodeposition. Two-dimensional activity distribution of hydrolytic enzymes participating in transformation of soil organics in the distance gradients from the root can be visualized under UV light by zymography - by placing a fluorogenic substrate-saturated membrane on the soil surface. Functional traits of enzymes can be co-localized with spatial distribution of enzymatic activity by precise micro-sampling based on zymography. We used rhizobox experiment to visualize activity of β-glucosidase, leucine aminopeptidase, and phosphatase in the rhizosphere of wild type and root hairless mutant of <em>Zea mays</em> L. cultivated for 3 weeks. After precise micro-sampling, we determined kinetic parameters of enzymes: max potential activity and affinity to substrate in the rhizosphere gradients. Finally, we compared the correspondence of enzymatic activity determined by zymography and by kinetic approach. This work was conducted within the framework of the priority program 2089, funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) – Project number: 403664478. Seeds of the maize were provided by Caroline Marcon and Frank Hochholdinger (University of Bonn).</p><p><strong>Keywords:</strong> zymography, enzyme kinetic, maize, rhizosphere gradients</p>

Transfer of Metals in Food Chain: An Example with Copper and Lettuce

Present study investigated the possible transfer of metals in the food chain (from soil to edible plants). The experiment was done with lettuce Lactuca sativa grown in different types of soil contaminated with copper (Cu2+) in various concentrations, with or without addition of humic substances. The highest content of copper was detected in lettuce samples grown in soils with lower levels of organic matter, thus indicating the importance of soil organics in metal transfer routes and accumulation rates in plants. It was found that copper accumulation in lettuce grown in contaminated soils can be significantly reduced by the addition of humic substances.