ABSTRACT
Landfill is one of the important sources of carbon tetrachloride (CT) pollution, and it is important to understand the degradation mechanism of CT in landfill cover for better control. In this study, a simulated landfill cover system was set up, and the biotransformation mechanism of CT and the associated micro-ecology were investigated. The results showed that three stable functional zones along the depth, i.e., aerobic zone (0-15 cm), anoxic zone (15-45 cm) and anaerobic zone (> 45 cm), were generated because of long-term biological oxidation in landfill cover. There were significant differences in redox condition and microbial community structure in each zone, which provided microbial resources and favorable conditions for CT degradation. The results of biodegradation indicated that dechlorination of CT produced chloroform (CF), dichloromethane (DCM) and Cl- in anaerobic and anoxic zones. The highest concentration of dechlorination products occurred at 30 cm, which were degraded rapidly in aerobic zone. In addition, CT degradation rate was 13.2-103.6 μg/(m2·d), which decreased with the increase of landfill gas flux. The analysis of diversity sequencing revealed that Mesorhizobium, Thiobacillus and Intrasporangium were potential CT-degraders in aerobic, anaerobic and anoxic zone, respectively. Moreover, six species of dechlorination bacteria and eighteen species of methanotrophs were also responsible for anaerobic transformation of CT and aerobic degradation of CF and DCM, respectively. Interestingly, anaerobic dechlorination and aerobic transformation occurred simultaneously in the anoxic zone in landfill cover. Furthermore, analysis of degradation mechanism suggested that generation of stable anaerobic-anoxic-aerobic zone by regulation was very important for the harmless removal of full halogenated hydrocarbon in vadose zone, and the increase of anoxic zone scale enhanced their removal. These results provide theoretical guidance for the removal of chlorinated pollutants in landfills.
Subject(s)
Bacteria/metabolism , Biodegradation, Environmental , Carbon Tetrachloride/metabolism , Methane/metabolism , Waste Disposal FacilitiesABSTRACT
To report a case of cutaneous and subcutaneous coinfection caused by Lichtheimia corymbifera and Candida parapsilosis.A 67-year-old female peasant consulted about proliferative granuloma developing on her left forearm after topical application of a Chinese herbal drug and splint fixation for the treatment of suspected fracture of the wrist.Direct microscopic examination showed gram positive budding yeast cells in lesion secretions.Pathological study with periodic acid-Schiff (PAS) and gormori methenamine silver (GMS) staining revealed broad non-separate hyphae in the corneum and dermis.Fungal culture of lesional tissue at 35℃ grew both mould and yeast.The mould was identified as Lichtheimia corymbifera based on morphological findings and sequences of the internal transcribed space (ITS) 1-4 regions.Thermal tolerance study revealed that the isolate grew fast at 37℃ but slowly at 40℃.Under a scanning electron microscope,the acrogenous sporangia were pear-shaped with conical sporangiophores originating from the top of stolon,which were among but not opposite to the rhizoids.The yeast was identified as Candida parapsilosis by Chromagar test and D1/D2 region sequencing.As antimicrobial susceptibility test indicated,the Lichtheimia corymbifera isolate was most sensitive to terbinafine and itraconazole.The proteolytic activity of Lichtheimia corymbifera was higher than that of Candida parapsilosis.The granuloma completely subsided after surgical resection and 6-week treatment with oral itraconazole 200 mg twice a day.No recurrence was observed during a 4-year follow-up.