Ecology of Organohalide-Respiring \u3ci\u3eDehalococcoides mccartyi\u3c/i\u3e: Corrinoid Cofactor-Related Community Interactions and Controls over Strain Selection

Organohalides such as tetrachloroethene (PCE) and trichloroethene (TCE) are among the most prevalent toxic groundwater contaminants. Remediation of organohalide-contaminated sites has high priority, and efficient and cost-effective remedies are needed to prevent environment and human exposure through contaminated water. Bacterial organohalide-respiration plays a major role in organohalide detoxification. Dehalococcoides mccartyi (Dhc) are key mediators in bioremediation, since only Dhc strains have been documented in complete detoxification of chlorinated ethenes to benign ethene. Dhc depends on other microorganisms in the environment for essential growth requirements (e.g., hydrogen and vitamins). For successful implementation of the reductive dechlorination to remediate contaminated sites, microbial interactions controlling Dhc reductive dechlorination must be elucidated. The overall objective of this research was to address the key gaps in the scientific understanding of the controls over Dhc reductive dechlorination activity, including Dhc corrinoid-related interactions with other microorganisms. Detailed hydrogeological and microbial characterization of mixed chlorinated solvent contaminated Third Creek site (Knoxville, TN) attributed an important role to the creek sediment, where organohalide-respiring bacteria (e.g., Dhc and Dehalobacter) co-exist, for detoxification of contaminants. Different chlorinated solvent-amendments affected Dhc strain selection and non-dechlorinating microbial composition in enrichment cultures derived from Third Creek sediment. Corrinoid-auxotroph Dhc require corrinoid cofactor for the reductive dehalogenase enzyme systems. Microorganisms including Acetobacterium, Clostridium, Geobacter, and methanogens were identified as corrinoid-producers in the enrichment cultures. 5,6-dimethyl-benzimidazole cobamide (DMB-Cba) was the most abundant corrinoid in enrichment cultures to support Dhc reductive dechlorination. Different lower base-amendments affected Dhc reductive dechlorination rates and extents. Lower base-amendments to enrichment cultures caused a shift from production of DMB-Cba to production of corrinoids with the amended lower bases, some of which caused lower dechlorination rates. In addition, different Dhc strains became abundant with different lower base-amendment in cultures, demonstrating the role of corrinoid in Dhc strain selection. Lastly this research demonstrated that different geochemical conditions and corresponding microbial populations determined the composition and concentration of bioavailable corrinoid pools; thus directly controlling Dhc reductive dechlorination activity. The findings of this research are relevant to environmental remediation practitioners and provide valuable information for improving bioremediation strategies to achieve successful contaminated-site cleanup

Stock price reaction to debt offerings: the Turkish evidence

We investigate the valuation effects of debt issues on the issuing firms’ common stock using a sample of Turkish issuers. For the sample of non-financial firms, we find no significant wealth effects for debt issues around the announcement dates. However, market reactions are more positive when information asymmetry between firm managers and outside investors is low, agency costs are high, and when debt issues are likely to carry positive information about firms’ prospects. These results support pecking order, signaling, and agency theories of capital structure. In additional tests, we find positive market reactions to debt issue announcements of financial firms

Investigations on nutrient recovery from anaerobic digestion residues with different compositions

TÜBİTAK ÇAYDAG01.06.2010Anaerobik bozundurma tarımsal ve hayvansal atık yönetiminde yaygın olarak kullanılan bir yöntemdir. Ancak, deşarj kriterlerini sağlayabilmek için anaerobik reaktör çıkış suları alıcı ortamlara verilmeden önce içerdiklerikleri besiyer maddelerin ayrıca arıtılması gerekmektedir. Strüvit çöktürme yöntemi bu amaç için kullanılan tekniklerden birisidir. Strüvit çöktürme yöntemi besiyer maddelerin anaerobik reaktör çıkış sularında etkin olarak giderilebilmesi için çok uygun bir yöntem olmakla birlikte, kullanımı büyük ölçüde faz ayrımı sonrası ayrılmış sıvı çıkış suları için uygulanmıştır. Bu nedenle bu projede anaerobik bozundurma sonrası reaktör çıkışında bulunan besiyer maddelerin (azot ve fosfor) hem sıvı hem katı fazda strüvit çöktürme yöntemi arıtım ve geri kazanımı araştırılmıştır.Anaerobic digestion (AD) is commonly used for the stabilization of agricultural and animal wastes. However, due to the stringent environmental criteria AD effluents need to be further treated to reduce nutrient loads to the receiving water bodies. Struvite precipitation is one of the promising techniques applied for this purpose. Even though several aspects of SP might be very significant for efficient nutrient removal, its application has been limited to the liquid phase of the phase-separated effluents only. Therefore, the removal and the recovery of nutrients, namely nitrogen (N) and phosphorus (P) from anaerobically digested and solid-liquid separated manure effluents via struvite precipitation were investigated. Both the liquid and the solid phases of the poultry manure digester effluent were subjected to struvite precipitation experiments in this project