Production of surfactin using pentose carbohydrate by Bacillus subtilis

Interest in microbial surfactants has been steadily increasing in recent years due to their diversity, mass production possibility, selectivity, performance under extreme conditions and potential applications in environmental protection. In this study two pentose sugars (xylose and arabinose) were investigated for the submerged fermentation (SmF) of Bacillus subtilis in surfactant production medium for bio-surfactant surfactin production. An excellent vegetative growth of B. subtilis (× 10¹⁰ CFU/mL) was observed for xylose and arabinose containing medium which were comparable to glucose supplemented medium. Low growth (× 10⁸ CFU/mL) was found when medium was not supplemented with any of the sugars. Surfactin production in xylose, arabinose and glucose containing medium was 2700, 2600 and 2000 mg/L, respectively, whereas, medium without any sugar showed low surfactin (700 mg/L) production. These results clearly indicate the effect of pentose sugars on production of surfactin. Gradual depletion of the xylose and arabinose were confirmed by HPLC analysis during the growth phase of the strain that ultimately produced the surfactin.     

Extending the inverse receptance coupling method for prediction of tool-holder joint dynamics in milling

Recently, receptance coupling substructure analysis (RCSA) is used for stability prediction of machine tools through its dynamic response determination. A major challenge is the proper modelling of the substructures joints and determination of their parameters. In this paper, a new approach for predicting tool tip FRF is presented. First, inverse RCSA formulation is extended so that the holder FRFs can be identified directly through experimental modal tests. The great advantage of this formulation is its implementation in arbitrary point numbers along joint length. Therefore, in comparison with previous inverse RCSA approaches, a more realistic joint model can be considered. In addition, due to applying the new approach, additional costly modal tests on the gauged tool are not required. This characteristic makes it possible to determine the holder FRFs without separating the tool; especially in situations where the holder end is inaccessible. The inclusion of joint parameters effect in the identified holder FRFs is another main advantage of such approach. Consequently, for identification of joint parameters, there is no need to use common error optimization based on fitting methods. The effect of overhang length is investigated through some analytical study and also experimental validation. Results show that the predicted tool tip FRF is exact in analytical case. Moreover, due to less noise effect, the predictions based on identified FRFs of longer tools are more accurate than the shorter ones (in experimental case).     

Production of iturin A homologues under different culture conditions

Iturin A is a cyclic lipopeptide antibiotic and eight different kinds of iturin A have been reported based on its alkyl side chains. As iturin A is a promising biocontrol agent, total production of iturin A was tried to enhance and comparative production of its homologues was investigated by using different nitrogen and carbon sources. When Polypepton S and defatted soybean meal were used, total production as well as the ratio of the iturin A homologues were similar. However, production of iturin A was relatively lower and also the ratio of the iturin A homologues was different when Polypepton was used, where A2 was decreased and A4 was increased. Production ratio of the iturin A homologues was similar for the carbon sources like maltose, mannitol, sucrose and starch but relative production of iturin A2 was much enhanced compared to A3 when lactose or galactose was used. Interestingly production ratio of A4 was increased and A2 and A3 were decreased when no additional carbon source was used, and similar tendency was observed in the homologue ratio with glucose and fructose. Production of iturin A homologue A6 was significantly increased whereas A2 and A3 were decreased when defatted rapeseed cake was used. Utilization of different amino acids did not show significant differences in their production of the iturin A homologues. Oxygen supply found to be the factor affecting the production of iturin A homologues when it was investigated in a varied culture volume size and shaking speed. A2 found to be increased with increased oxygen supply where the production of A3 was affected inversely.     

天山西部伊犁河流域土壤盐分特征

采用相关分析法与主成分分析法研究了伊犁河流域土壤盐分特征.结果表明:研究区域耕层(3～20 cm)土壤53.68%样地为非盐渍化土壤,18.38%为轻度盐渍化,13.97%为中度盐渍化,8.82%为重度盐渍化,5.15%为盐土;土壤盐渍化类型以硫酸盐渍土为主,占68.41%.盐分组成中,阴离子以SO₄2-和Cl-为主,阳离子以Na+和Ca2+为主;土壤盐分与Cl-和SO₄2-分别呈极显著、显著正相关关系,揭示了土壤盐分大小与w(Cl-)和w(SO₄2-)有关;表层(0～3 cm)土壤盐分平均值占0～60 cm土层盐分平均值的60.19 %,即土壤盐分垂直分布呈现强烈表聚性.主成分分析结果表明,盐分,w(Cl-),w(SO₄2-),w(Mg2+)与w(Ca2+)可作为研究区域土壤盐渍化状况的特征因子.不同土地利用类型条件下,耕层土壤盐分平均值从高到低依次为草地、旱田、稻田、林地.不同灌溉条件下,井灌农田耕层土壤盐分平均值为1.12 g/kg,渠灌农田耕层土壤盐分平均值为0.73 g/kg,渠灌农田耕层土壤盐分平均值比井灌农田小0.39 g/kg.不同时期耕层土壤盐分平均值从高到低依次为非灌溉期、夏灌期、秋灌期.      

Bioaccumulation of heavy metals in fish species of Iran: a review

Environmental Geochemistry and Health - Accumulation of heavy metals (HMs) in fish tissues is an important factor in monitoring the health and safety of aquatic ecosystems. Furthermore, fish are...     

Vertical distribution and contamination assessment of heavy metals in sediment cores of ship breaking area of Bangladesh

Environmental Geochemistry and Health - Vertical heavy metal profiling reflects the history of the deposition of metals and helps to understand the characteristics of accumulation in various layers...     

Seasonal variations of polycyclic aromatic hydrocarbons in coastal sediments of a marine resource hot spot: the case of pars special economic energy zone,Iran

Environmental Geochemistry and Health - Polycyclic aromatic hydrocarbons (PAHs) are an important group of compounds of major environmental concern, which are in the class of persistent organic...     

Silica-supported antimony(III) chloride as a mild and reusable catalyst for the Paal–Knorr pyrrole synthesis

Heterogeneous catalysts are used for control of environmental pollution. Heterogeneous catalysts are easily separated from the reaction mixture, thus allowing their recovery and re-use. There is a need for catalysts that are efficient under mild conditions. Here, we show that silica-supported antimony(III) chloride (SbCl₃/SiO₂) acts as a highly efficient heterogeneous Lewis acid catalyst for the Paal–Knorr pyrrole synthesis at room temperature. We found that condensation of hexane-2,5-dione with aromatic and aliphatic primary amines in hexane using SbCl₃/SiO₂ with 7.6 wt% SbCl₃ was the best reaction condition. The silica support facilitated the workup of the reaction mixture and provided a reusable catalyst at least for 7 runs without significant loss in activity. Indeed, the yield was 98% for the first run and 84% for the 7th run. We conclude that low catalyst loading, operational simplicity, practicability and applicability to various substrates make this reaction an interesting alternative to previously applied procedures. From the environmental standpoint, this eco-friendly catalyst is stable, highly active, easy to prepare and handle.