Molecular ecology of facultative methanotrophs

Methylocella spp. are facultative methanotrophs, able to grow not only on one carbon molecules e.g., methane or methanol, but also on multi-carbon compounds e.g., acetate, succinate and malate. PCR-based molecular techniques were developed and validated to target the 16S rRNA genes of all the species of the genus Methylocella present in environmental samples. DNA extracted from a variety of environmental samples screened by PCR to determine the environmental distribution of Methylocella spp. Methylocella were found to be widely distributed, not only in acidic environments, but also in neutral and alkaline environments. New primers targeting the mmoX gene of Methylocella spp. that encoded the α-subunit of methane monooxygenases were designed. A SYBR® green-based real-time quantitative PCR assay was developed and validated using these Methylocella mmoX gene-targeting primers. The abundance of Methylocella spp. present in selected environmental samples was quantified using the newly developed real-time quantitative PCR assay A series of 13CH4 DNA-SIP experiments were carried either in the presence or absence of 12C acetate in microcosms containing Moor House peat soil to investigate the effect of acetate (0.5 mM) on the ability of Methylocella silvestris to oxidize methane. Methane oxidation data indicated that acetate repressed the ability of Methylocella silvestris to oxidize methane in peat soil microcosms. 13CH4 DNA-SIP experiments revealed that in presence of acetate, Methylocella silvestris did not utilize methane as a carbon source, suggesting that acetate might be the alternative source of carbon. However, when 13C-labelled acetate DNA-SIP experiments were carried out, Methylocella spp. were not found to be dominant acetate utilizers in the peat soil microcosms. Methylocella spp. seem to have been outcompeted by more efficient acetate utilizers such as Brevundimonas and Burkholderia. To identify genes that might be involved in the utilization of methane or acetate, Methylocella silvestris whole genome transcriptomics experiments were carried out. All the genes of the sMMO gene cluster were found to be highly upregulated during growth on methane. In addition to the sMMO gene cluster, a gene encoding Fur was also found to be highly upregulated during growth on methane. During growth on acetate, a gene cluster encoding glycine dehydrogenase was found to be highly upregulated. Microarray experiments carried out here provided potential candidate genes for further characterization by gene knockout based studies. Further work is also required to validate the microarray findings. A study was carried out on forest soils derived from Swedish islands that were at different successional stages. All islands were found to be positive for the presence of Methylocella spp., and identity of composition of other methanotrophs were determined using a pmoA-diagnostic microarray. All the islands were dominated by Methylococcus, Methylosinus and methanotrophs of the uncultivated RA14 clade. The diversity of methanotrophs was higher in late successional islands compared to mid and early successional islands. In addition the diversity of methanotrophs decreased as the soil depth increased

Metal-Coated Defect-Core Photonic Crystal Fiber for THz Propagation

Modal solutions for metal-coated defect-core photonic crystal fiber (PCF) with a central air-hole have been obtained by using a full-vectorial finite element method to model the guidance of THz waves. It has been shown that the surface plasmon modes can couple with the defect-core PCF mode to form supermodes, with potential for sensing applications

Molecular ecology of facultative methanotrophs

Methylocella spp. are facultative methanotrophs, able to grow not only on one carbon molecules e.g., methane or methanol, but also on multi-carbon compounds e.g., acetate, succinate and malate. PCR-based molecular techniques were developed and validated to target the 16S rRNA genes of all the species of the genus Methylocella present in environmental samples. DNA extracted from a variety of environmental samples screened by PCR to determine the environmental distribution of Methylocella spp. Methylocella were found to be widely distributed, not only in acidic environments, but also in neutral and alkaline environments. New primers targeting the mmoX gene of Methylocella spp. that encoded the α-subunit of methane monooxygenases were designed. A SYBR® green-based real-time quantitative PCR assay was developed and validated using these Methylocella mmoX gene-targeting primers. The abundance of Methylocella spp. present in selected environmental samples was quantified using the newly developed real-time quantitative PCR assay A series of 13CH4 DNA-SIP experiments were carried either in the presence or absence of 12C acetate in microcosms containing Moor House peat soil to investigate the effect of acetate (0.5 mM) on the ability of Methylocella silvestris to oxidize methane. Methane oxidation data indicated that acetate repressed the ability of Methylocella silvestris to oxidize methane in peat soil microcosms. 13CH4 DNA-SIP experiments revealed that in presence of acetate, Methylocella silvestris did not utilize methane as a carbon source, suggesting that acetate might be the alternative source of carbon. However, when 13C-labelled acetate DNA-SIP experiments were carried out, Methylocella spp. were not found to be dominant acetate utilizers in the peat soil microcosms. Methylocella spp. seem to have been outcompeted by more efficient acetate utilizers such as Brevundimonas and Burkholderia. To identify genes that might be involved in the utilization of methane or acetate, Methylocella silvestris whole genome transcriptomics experiments were carried out. All the genes of the sMMO gene cluster were found to be highly upregulated during growth on methane. In addition to the sMMO gene cluster, a gene encoding Fur was also found to be highly upregulated during growth on methane. During growth on acetate, a gene cluster encoding glycine dehydrogenase was found to be highly upregulated. Microarray experiments carried out here provided potential candidate genes for further characterization by gene knockout based studies. Further work is also required to validate the microarray findings. A study was carried out on forest soils derived from Swedish islands that were at different successional stages. All islands were found to be positive for the presence of Methylocella spp., and identity of composition of other methanotrophs were determined using a pmoA-diagnostic microarray. All the islands were dominated by Methylococcus, Methylosinus and methanotrophs of the uncultivated RA14 clade. The diversity of methanotrophs was higher in late successional islands compared to mid and early successional islands. In addition the diversity of methanotrophs decreased as the soil depth increased.EThOS - Electronic Theses Online ServiceUniversity of WarwickUniversity of Warwick. Dept. of Biological SciencesGBUnited Kingdo

Higher Order Lateral Mode Suppression Schemes for Edge Emitting Terahertz Quantum Cascade Laser Waveguides

The modal performance of a slot-clad metal-metal waveguide for terahertz quantum cascade lasers (QCLs) is elucidated in this study. Terahertz QCLs, based on metal-metal waveguides having a large ridge width, are susceptible to lase with higher order lateral modes, which may produce poor quality beams and can lead to detrimental consequences for certain applications. By comparing the modal performance of the slot-clad waveguide with previously reported designs, it has been shown that the slot-clad metal-metal waveguide can significantly enhance the degree of suppression of higher order lateral modes

Low-loss Waveguides for THz Guidance and Devices

The terahertz (THz) region occupies a large portion of the electromagnetic spectrum, located between the microwave and optical frequencies and normally is defined as the band ranging from 0.1 to 10 THz. In recent years, this intermediate THz radiation band has attracted considerable interest, because it offers significant scientific and technological potential for applications in many fields, such as sensing [1], imaging [2] and spectroscopy [3]. However, waveguiding in this intermediate spectral region is a major challenge and strong dielectric and conductive losses in the terahertz frequency range have been a major problem for waveguiding. The conventional guiding structures exemplified by microstrips, coplanar striplines and coplanar waveguides [4] are highly lossy and dispersive. However, so far the most promising dielectric waveguides have been the use of photonic crystal fibers at terahertz frequencies [5, 6] and metal coated guides [7] at terahertz frequencies. In this paper, various types of practical dielectric and metal coated waveguides are evaluated and design optimization of Quantum Cascade Lasers, MMI-based power splitters and narrow-band filters are presented, by using full-vectorial finite element method [8]. © (2013) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only

Multimode Interference 3 dB Splitters in Hollow Core Metallic Waveguides for Low-Loss THz Wave Transmission

A multimode interference half-power splitter on hollow core polysterene-coated metallic waveguide is demonstrated in this study. The modal properties, propagation length, optical field evolution, and dispersion of the aforementioned device have been investigated using the full vectorial finite-element-based modal analysis and beam propagation method, as well as the finite-difference time-domain approach

Low-dose β-carotene Supplementation and Deworming Improve Serum Vitamin A and β-carotene Concentrations in Preschool Children of Bangladesh

Despite the national vitamin A and antihelminthic prophylaxis programmes, both intestinal geo-helminths and subclinical vitamin A deficiency continue to be prevalent among children in developing countries. Studies on potential synergistic effects of vitamin A supplementation and deworming on retinol status have inconsistent results. The purpose of the present study was to investigate the impacts of low-dose β-carotene supplementation and antihelminthic therapy on serum retinol and β-carotene concentrations in preschool children of Bangladesh. Two hundred and forty-four children, known to be infected with Ascaris lumbricoides, were randomized into four treatment groups: I-IV. Group I and II received two oral doses of 400 mg of albendazole each, the first dose at baseline and the second dose after four months; Group III and IV received placebo in place of albendazole. In addition, Group I and III received 1.2 mg of β-carotene powder in capsule daily for six months, and Group II and IV received placebo in place of β-carotene. Serum retinol and β-carotene levels were measured before and after six months of the interventions. Serum retinol and β-carotene increased significantly in Group I where both antihelminthic therapy and daily β-carotene supplementation were given (p<0.05 and p<0.001 respectively). Antihelminthic therapy alone only improved serum β-carotene concentration (p<0.0001). Low-dose β-carotene supplementation, along with an antihelminthic therapy, synergistically improved vitamin A status. This finding has public-health implications for improving vitamin A status of children in developing countries