Evolution of diverse effective N2-fixing microsymbionts of Cicer arietinum following horizontal transfer of the Mesorhizobium ciceri CC1192 symbiosis integrative and conjugative element.

Rhizobia are soil bacteria capable of forming N2-fixing symbioses with legumes, with highly effective strains often selected in agriculture as inoculants to maximize symbiotic N2 fixation. When rhizobia in the genus Mesorhizobium have been introduced with exotic legumes into farming systems, horizontal transfer of symbiosis Integrative and Conjugative Elements (ICEs) from the inoculant strain to soil bacteria has resulted in the evolution of ineffective N2-fixing rhizobia that are competitive for nodulation with the target legume. In Australia, Cicer arietinum (chickpea) has been inoculated since the 1970's with Mesorhizobium ciceri sv. ciceri CC1192, a highly effective strain from Israel. Although the full genome sequence of this organism is available, little is known about the mobility of its symbiosis genes and the diversity of cultivated C. arietinum-nodulating organisms. Here, we show the CC1192 genome harbors a 419-kb symbiosis ICE (ICEMcSym1192) and a 648-kb repABC-type plasmid pMC1192 carrying putative fix genes. We sequenced the genomes of 11 C. arietinum nodule isolates from a field site exclusively inoculated with CC1192 and showed they were diverse unrelated Mesorhizobium carrying ICEMcSym1192, indicating they had acquired the ICE by environmental transfer. No exconjugants harboured pMc1192 and the plasmid was not essential for N2 fixation in CC1192. Laboratory conjugation experiments confirmed ICEMcSym1192 is mobile, integrating site-specifically within the 3' end of one of the four ser-tRNA genes in the R7ANS recipient genome. Strikingly, all ICEMcSym1192 exconjugants were as efficient at fixing N2 with C. arietinum as CC1192, demonstrating ICE transfer does not necessarily yield ineffective microsymbionts as previously observed.Importance Symbiotic N2 fixation is a key component of sustainable agriculture and in many parts of the world legumes are inoculated with highly efficient strains of rhizobia to maximise fixed N2 inputs into farming systems. Symbiosis genes for Mesorhizobium spp. are often encoded chromosomally within mobile gene clusters called Integrative and Conjugative Elements or ICEs. In Australia, where all agricultural legumes and their rhizobia are exotic, horizontal transfer of ICEs from inoculant Mesorhizobium strains to native rhizobia has led to the evolution of inefficient strains that outcompete the original inoculant, with the potential to render it ineffective. However, the commercial inoculant strain for Cicer arietinum (chickpea), M. ciceri CC1192, has a mobile symbiosis ICE (ICEMcSym1192) which can support high rates of N2 fixation following either environmental or laboratory transfer into diverse Mesorhizobium backgrounds, demonstrating ICE transfer does not necessarily yield ineffective microsymbionts as previously observed

Functional-structural modelling of faba bean

Crop models such as CERES and CropSyst treat canopies as homogeneous entities without attempting to define canopy geometry, other than through row structure, nor deal with growth processes at time steps shorter than one day. A functional-structural modelling approach can improve canopy simulation, in particular of indeterminate crops such as faba bean. A major challenge is to incorporate the plasticity of the canopy. Functional-structural models can accomplish this by introducing variation in several ways and at different levels of canopy composition. ALAMEDA is a functional-structural model of a faba bean (Vicia faba L.) crop that addresses these issues. An L-system provides the basic conceptual and program structure within which functional relationships can be connected. In this way it plays a comparable role to physical plant structure that provides the linkage between morphology and physiological processes spatially distributed over plant components. In accordance with results of previous studies with faba bean, the stem was selected as the main building module. An associated growth model is linked to calculate the lengths of the vegetative organs, and leaf allometries are used to compute leaf area. ALAMEDA is currently being extended by including a model of radiation interception and functions from classic models, for example, the variation of specific leaf area with temperature as specified in CROPGRO-legume

Kinetics of sulfation of chalcopyrite with steam and oxygen in the presence of ferric oxide

The kinetics of sulfation of chalcopyrite with/without ferric oxide addition has been studied in the fixed bed for the temperature range 673 to 773 K in the absence of external mass transfer effects such as particle size of ore and flow rate of oxidizing gases such as steam and oxygen. The sulfation reaction was observed to be topochemical. The activation energy value of 30.5 kJ/mol was found when no catalytic addition was made. The rate of sulfation increases with the addition of ferric oxide. The rate constant values obtained without and with 10 pet Fe2O3 were 5.5 x 10(3) min(-1) and 7.00 x 10(3) min(-1), respectively. The activation energy value for the roasting in the presence of the catalyst was 29.2 kJ/mol under these conditions. Examination of the kinetic data indicates that the reaction occurred on the surface of the mineral particles and proceeded through the reactant and product phase boundary. The sulfated products were also characterized by metallography, scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), and X-ray diffractometry (XRD) studies