Dynamics of bacterial and archaeal communities during horse bedding and green waste composting.

Organic waste decomposition can make up substantial amounts of municipal greenhouse emissions during decomposition. Composting has the potential to reduce these emissions as well as generate sustainable fertilizer. However, our understanding of how complex microbial communities change to drive the chemical and biological processes of composting is still limited. To investigate the microbiota associated with organic waste decomposition, initial composting feedstock (Litter), three composting windrows of 1.5 months (Young phase), 3 months (Middle phase) and 12 months (Aged phase) old, and 24-month-old mature Compost were sampled to assess physicochemical properties, plant cell wall composition and the microbial community using 16S rRNA gene amplification. A total of 2,612 Exact Sequence Variants (ESVs) included 517 annotated as putative species and 694 as genera which together captured 57.7% of the 3,133,873 sequences, with the most abundant species being Thermobifida fusca, Thermomonospora chromogena and Thermobifida bifida. Compost properties changed rapidly over time alongside the diversity of the compost community, which increased as composting progressed, and multivariate analysis indicated significant variation in community composition between each time-point. The abundance of bacteria in the feedstock is strongly correlated with the presence of organic matter and the abundance of plant cell wall components. Temperature and pH are the most strongly correlated parameters with bacterial abundance in the thermophilic and cooling phases/mature compost respectively. Differential abundance analysis revealed 810 ESVs annotated as species significantly varied in relative abundance between Litter and Young phase, 653 between the Young and Middle phases, 1182 between Middle and Aged phases and 663 between Aged phase and mature Compost. These changes indicated that structural carbohydrates and lignin degrading species were abundant at the beginning of the thermophilic phase, especially members of the Firmicute and Actinobacteria phyla. A high diversity of species capable of putative ammonification and denitrification were consistently found throughout the composting phases, whereas a limited number of nitrifying bacteria were identified and were significantly enriched within the later mesophilic composting phases. High microbial community resolution also revealed unexpected species which could be beneficial for agricultural soils enriched with mature compost or for the deployment of environmental and plant biotechnologies. Understanding the dynamics of these microbial communities could lead to improved waste management strategies and the development of input-specific composting protocols to optimize carbon and nitrogen transformation and promote a diverse and functional microflora in mature compost.

Glyphosate has a negligible impact on bacterial diversity and dynamics during composting.

The herbicide glyphosate has several potential entry points into composting sites and its impact on composting processes has not yet been evaluated. To assess its impact on bacterial diversity and abundance as well as on community composition and dynamics, we conducted a mesocosm experiment at the Montreal Botanical Garden. Glyphosate had no effect on physicochemical property evolution during composting, while it was completely dissipated by the end of the experiment. Sampling at Days 0, 2, 28 and 112 of the process followed by 16S rRNA amplicon sequencing also found no effect of glyphosate on species richness and community composition. Differential abundance analyses revealed an increase of a few taxa in the presence of glyphosate, namely TRA3-20 (order Polyangiales), Pedosphaeraceae and BIrii41 (order Burkholderiales) after 28 days. In addition, five amplicon sequence variants (ASVs) had lower relative abundance in the glyphosate treatment compared to the control on Day 2, namely Comamonadaceae, Pseudomonas sp., Streptomyces sp., Thermoclostridium sp. and Actinomadura keratinilytica, while two ASVs were less abundant on Day 112, namely Pedomicrobium sp. and Pseudorhodoplanes sp. Most differences in abundance were measured between the different sampling points within each treatment. These results present glyphosate as a poor determinant of species recruitment during composting.

Dissipation and effect of glyphosate during composting of organic wastes.

The addition of organic matter (OM) containing glyphosate during compost production, through the introduction of contaminated plant residues or sewage sludge, presents a risk of hindering the proper OM breakdown carried out by microorganisms and causing the accumulation of glyphosate or aminomethylphosphonic acid (AMPA). To measure the effect of glyphosate and glyphosate-based herbicide (GBH) on OM decomposition as well as the dissipation of glyphosate to AMPA during composting, a controlled-environment experiment was conducted using mesocosm-scale vessels. Analytical-grade (AG) glyphosate (150 mg kg-1 ) and GBH (VisionMAX) equivalent to the amounts applied in agricultural areas (300 mg kg-1 ) were added to a mixture of green residues, which were then composted for 112 d. Sampling after 2, 7, 28, and 112 d showed a negligible effect of glyphosate and GBH on physicochemical properties of the mixture (temperature, OM%, pH, total carbon [C], total nitrogen [N], and C/N ratio), ammonification, nitrification, and phosphate content. No differences between AG glyphosate and GBH treatments were measured. Glyphosate levels decreased significantly after 2 d to reach 53.1 and 71.1% of the initial content for the AG glyphosate and GBH treatments, respectively, and glyphosate dissipation was almost complete after 112 d of composting. Aminomethylphosphonic acid could not be detected at any time during the experiment regardless of the treatment. Our results show that conditions for OM decomposition were maintained despite the addition of glyphosate and suggest that only trace amounts of glyphosate or AMPA are likely to be present in mature compost.

Neuropilin-1 expression in adipose tissue macrophages protects against obesity and metabolic syndrome.

Obesity gives rise to metabolic complications by mechanisms that are poorly understood. Although chronic inflammatory signaling in adipose tissue is typically associated with metabolic deficiencies linked to excessive weight gain, we identified a subset of neuropilin-1 (NRP1)-expressing myeloid cells that accumulate in adipose tissue and protect against obesity and metabolic syndrome. Ablation of NRP1 in macrophages compromised lipid uptake in these cells, which reduced substrates for fatty acid ß-oxidation and shifted energy metabolism of these macrophages toward a more inflammatory glycolytic metabolism. Conditional deletion of NRP1 in LysM Cre-expressing cells leads to inadequate adipose vascularization, accelerated weight gain, and reduced insulin sensitivity even independent of weight gain. Transfer of NRP1+ hematopoietic cells improved glucose homeostasis, resulting in the reversal of a prediabetic phenotype. Our findings suggest a pivotal role for adipose tissue-resident NRP1+-expressing macrophages in driving healthy weight gain and maintaining glucose tolerance.