Expanding Characterized Diversity and the Pool of Complete Genome Sequences of Methylococcus Species, the Bacteria of High Environmental and Biotechnological Relevance

The bacterial genus Methylococcus, which comprises aerobic thermotolerant methanotrophic cocci, was described half-a-century ago. Over the years, a member of this genus, Methylococcus capsulatus Bath, has become a major model organism to study genomic and metabolic basis of obligate methanotrophy. High biotechnological potential of fast-growing Methylococcus species, mainly as a promising source of feed protein, has also been recognized. Despite this big research attention, the currently cultured Methylococcus diversity is represented by members of the two species, M. capsulatus and M. geothermalis, while finished genome sequences are available only for two strains of these methanotrophs. This study extends the pool of phenotypically characterized Methylococcus strains with good-quality genome sequences by contributing four novel isolates of these bacteria from activated sludge, landfill cover soil, and freshwater sediments. The determined genome sizes of novel isolates varied between 3.2 and 4.0Mb. As revealed by the phylogenomic analysis, strains IO1, BH, and KN2 affiliate with M. capsulatus, while strain Mc7 may potentially represent a novel species. Highest temperature optima (45–50°C) and highest growth rates in bioreactor cultures (up to 0.3h−1) were recorded for strains obtained from activated sludge. The comparative analysis of all complete genomes of Methylococcus species revealed 4,485 gene clusters. Of these, pan-genome core comprised 2,331 genes (on average 51.9% of each genome), with the accessory genome containing 846 and 1,308 genes in the shell and the cloud, respectively. Independently of the isolation source, all strains of M. capsulatus displayed surprisingly high genome synteny and a striking similarity in gene content. Strain Mc7 from a landfill cover soil differed from other isolates by the high content of mobile genetic elements in the genome and a number of genome-encoded features missing in M. capsulatus, such as sucrose biosynthesis and the ability to scavenge phosphorus and sulfur from the environment.

Methane Oxidation Biosystem In Landfill Fugitive Emissions Using Conventional Cover Soil And Compost As Alternative Substrate – A Field Study

Landfill is an important anthropogenic source of greenhouse gases (GHG). Aiming at methane mitigation through the use of a cover layer in the form of fugitive emissions, this study investigated the methane passive bioxidation in a Brazilian landfill in biofilters under two conditions: control column (packing material using a 60 cm landfill cover soil with ≅0.8% organic matter) and enriched column (packing material using 45 cm landfill cover soil and 15 cm mixture of cover soil plus compost with ≅6% organic matter). The biogas was collected from a vertical drain pipe of a four-year-old cell and injected into the base of the columns with a high inlet loading (1000 g CH4 .m - ².d - ¹ at standard temperature and pressure conditions) in the upward flow mode. Ten campaigns were carried out for six months in order to determine the efficiency of the methane oxidation in each column. Parameters related to the biogas oxidation were also determined, such as soil temperature and moisture content and nutrients content in both filter beds. The oxidation global efficiencies were higher in the enriched column throughout all campaigns, with »71 and »95% for the control and enriched columns, respectively. Our study demonstrated that the use of substrates with high organic matter content and low cost (such as the compost) in landfill cover layers might present high efficacy in the reduction of methane fugitive emissions. Landfill is an important anthropogenic source of greenhouse gases (GHG). Aiming at methane mitigation through the use of a cover layer in the form of fugitive emissions, this study investigated the methane passive bio-oxidation in a Brazilian landfill in biofilters under two conditions: control column (packing material using only landfill cover soil with ≅0.8% organic matter) and enriched column (packing material using 45 cm landfill cover soil and 15 cm mixture of cover soil plus compost with ≅6% organic matter). Biogas was collected from a vertical drain pipe of a four-year-old cell and injected into the base of the columns with a high inlet loading (1000 gCH4.m-².d-¹) in upward flow mode. Ten campaigns were carried out for six months in order to determine the efficiency of the methane oxidation in each column. Soil temperature, moisture and nutrients content in both filter beds were also determined. The oxidation global efficiencies were higher in the enriched column throughout all campaigns, with »71 and »95% for the control and enriched columns, respectively, demonstrating that this technology can be applied even in landfills where there is no energy recovery from biogas (as in most landfills in developing countries). Our study demonstrated that the use of substrates with high organic matter content and low cost in landfill cover layers might present high efficacy in the reduction of methane fugitive emissions. Even operating in field-scale conditions, the results of this study were comparable to those obtained with biofilters on lab-scale (under controlled operational conditions).

Estudo da fertilidade dos solos de cobertura de um aterro sanitário do Estado do Ceará (Nordeste, Brasil)

<p class="yiv0149913358msonormal">This study was aimed to evaluate the fertility potential of a landfill cover soil in the State of Ceará (Northeastern Brazil) as a substrate for the survival and development of a vegetation cover. Four cover soil sampling points were chosen and simple samples were collected (500 g) at two different depths (0-20 cm and 20-40 cm), adding up to 16 samples (1st campaign: August 2014, 2nd campaign: December 2014) that were tested for 20 chemical attributes. Most attributes indicated a favorable condition for the survival and development of a vegetation cover. There was a major trend of decreased concentration of the tested attributes with depth, in agreement with the available literature. Considering that there are large trees in the studied area and no fallen trees were found, it seems that the cover soil has allowed for a good root fixation.</p>

Geotechnical Characterization of Biochar-Based Biocover

Landfills are one of the major sources of methane (CH4) emission which is a very potent greenhouse gas. The use of a natural process for microbial CH4 oxidation through biocovers provides a source reduction of CH4 emission. Previous studies have mostly focused on biochemical properties, and limited research has been conducted with regards to the geotechnical characterization of biochar based biocovers. This paper presents the results of a comprehensive laboratory investigation on laterite, Igbokoda sand and their mixtures with biochar at 2%, 4%, 8%, 10% and 20% to determine the compaction properties of biochar based biocovers. From the result, it was shown that the laterite has medium plasticity while the Igbokoda sand is non-plastic. Also, Addition of biochar to landfill cover soil increased the particle sizes, and consequently the porosity of the soil is increased which can promote the air flow through the landfill cover. Thus, greater O2 diffusion within the landfill cover will result, leading to higher microbial oxidation/degradation of CH4. Maximum dry unit weight decreased and the optimum water content partly increased as the biochar content increased with the two samples. Compaction test results show that when biochar content varied from 0 to 20% for the laterite, the maximum dry unit weight decreased from 1660kg/m3 to 1330kg/m3 and decreased from 1590kg/m3 to 1390kg/m3 for Igbokoda Sand. Thus, the results presented in this paper will contribute to a better understanding of the geotechnical behaviour of biochar based biocover.