Shifting abundances of communities associated with nitrogen cycling in soils promoted by sugarcane harvest systems

Sugarcane cultivation supports Brazil as one of the largest world sugar and ethanol producer. In order to understand the impact of changing sugarcane harvest from manual to mechanized harvest, we studied the effect of machinery traffic on soil and consequently soil compaction upon soil microbial communities involved in nitrogen cycling. The impact of sugarcane harvest was dependent on soil depth and texture. At deeper soil layers, mechanized harvesting increases the abundance of nitrogen fixers and denitrifying communities (specifically nosZ clade I and II) while manual harvesting increases the abundance of ammonia oxidizers (specifically AOA) and increases denitrifying communities (nosZ clade I and II) on top and at intermediate depth. The effect of change on the harvest system is more evident on sandy soil than on clay soil, where soil indicators of compaction (bulk density and penetration resistance) were negatively correlated with soil microorganisms associated with the nitrogen cycle. Our results point to connections between soil compaction and N transformations in sugarcane fields, besides naming biological variables to be used as proxies for alterations in soil structure.     

Synthesis,antiproliferative and antibacterial activity of new amides of salinomycin

A series of 11 novel amides of salinomycin were synthesized for the first time. All the obtained compounds were found to show potent antiproliferative activity against human cancer cell lines including the drug-resistant cancer cells. Four new salinomycin derivatives revealed good antibacterial activity against clinical isolates of methicillin-resistant Staphylococcus epidermidis (MRSE).     

Transmission of the mycoparasite Coniothyrium minitans by collembolan Folsomia Candida (Collembola: Entomobryidae) and glasshouse sciarid Bradysia sp. (Diptera: Sciaridae)

Folsomia Candida was maintained on potato dextrose agar (PDA) plates precolonised by the mycoparasite Coniothyrium minitans for 3 yr but the sciarid Bradysia sp. survived for a maximum of only three generations. Collembolans and sciarid larvae from these cultures were able to transmit C. minitans to uninoculated PDA plates through the survival of spores in faecal pellets. Adult and larval sciarids also transmitted C. minitans from PDA culture to uninoculated PDA plates by contamination on the cuticle. In soil and sand both sciarids and collembolans were able to transmit C. minitans from C. m/m'tans-inoculated to uninoculated sclerotia of Sclerotinia sclerotiorum. Inoculation of sclerotia with C. minitans enabled greater populations of larger collembolans to develop. In the glasshouse where C. minitans had been applied to the soil, one adult sciarid and four collembolans out of 70 and 101 insects collected respectively yielded C. minitans on placement onto PDA + Aureomycin.     

Evaluation of automated analysis of 15N and total N in plant material and soil

Simultaneous determination of ¹⁵N and total N using an automated nitrogen analyser interfaced to a continuous-flow isotope ratio mass spectrometer (ANA-MS method) was evaluated. The coefficient of variation (CV) of repeated analyses of homogeneous standards and samples at natural abundance was lower than 0.1%. The CV of repeated analyses of ¹⁵N-labelled plant material and soil samples varied between 0.3% and 1.1%. The reproductibility of repeated total N analyses using the automated method was comparable to results obtained with a semi-micro Kjeldahl procedure. However, the automated method gave results which were 3% to 5% higher than those obtained with the Kjeldahl procedure. Since only small samples can be analysed, careful sample homogenization and fine grinding are very important. Evaluation of a diffusion method for preparing nitrate and ammonium in solution for automated ¹⁵N analysis showed that the recovery of inorganic N in the NH₃ trap was lower when the N was diffused from water than from 2 M KCl. The results also indicated that different proportions of the NO₃ ^- and the NH₄ ⁺ in aqueous solution were recovered in the trap after combined diffusion. The method is most suited for diffusing either NO₃ ^- or NH₄ ⁺ alone, but can be used for combined diffusion of the two ions.     

Soil structural aspects of decomposition of organic matter by micro-organisms

Soil architecture is the dominant control over microbially mediated decomposition processes in terrestrial ecosystems. Organic matter is physically protected in soil so that large amounts of well-decomposable compounds can be found in the vicinity of largely starving microbial populations. Among the mechanisms proposed to explain the phenomena of physical protection in soil are adsorption of organics on inorganic clay surfaces and entrapment of materials in aggregates or in places inaccessible to microbes. Indirect evidence for the existence of physical protection in soil is provided by the occurrence of a burst of microbial activity and related increased decomposition rates following disruption of soil structures, either by natural processes such as the remoistening of a dried soil or by human activities such as ploughing. In contrast, soil compaction has only little effect on the transformation of ¹⁴C-glucose. Another mechanism of control by soil structure and texture on decomposition in terrestrial ecosystems is through their impact on microbial turnover processes. The microbial population is not only the main biological agent of decomposition in soil, it is also an important, albeit small, pool through which most of the organic matter in soil passes. Estimates on the relative importance of different mechanisms controlling decomposition in soil could be derived from results of combined tracer and modelling studies. However, suitable methodology to quantify the relation between soil structure and biological processes as a function of different types and conditions of soils is still lacking.     

Histological and mechanical evaluation of antifreeze peptide (Afp1m) cryopreserved skin grafts post transplantation in a rat model

The objective of this study was to evaluate the use of Afp1m as a cryopreservative agent for skin by examining the transplanted skin histological architecture and mechanical properties following subzero cryopreservation. Thirty four (34) rats with an average weight of 208 ± 31 g (mean ± SD), were used. Twenty four (n = 24) rats were equally divided into four groups: (i) immediate non-cryopreserved skin autografts (onto same site), (ii) immediate non-cryopreserved skin autografts (onto different sites), (iii) skin autografts cryopreserved with glycerol for 72 h and (iv) skin autografts cryopreserved with Afp1m for 72 h at −4 °C. Rounded shaped full-thickness 1.5–2.5 cm in diameter skin was excised from backs of rats for the autograft transplantation. Non-cryopreserved or cryopreserved auto skin graft were positioned onto the wound defects and stitched. Non-transplanted cryopreserved and non-cryopreserved skin strips from other ten rats (n = 10) were allowed for comparative biomechanical test. All skin grafts were subjected to histological and mechanical examinations at the end of day 21. Histological results revealed that tissue architecture especially the epidermal integrity and dermal-epidermal junction of the Afp1m cryopreserved skin grafts exhibited better histological appearance, good preservation of tissue architecture and structural integrity than glycerolized skin. However, there was no significant difference among these groups in other histological criteria. There were no significant differences among the 4 groups in skin graft mechanical properties namely maximum load. In conclusion, Afp1m were found to be able to preserve the microstructure as well as the viability and function of the skin destined for skin transplantation when was kept at −4 °C for 72 h.