Primary settling changes the microbial community of influent wastewater to wastewater treatment plants.

The continuous immigration of bacteria in influent wastewater strongly impacts the microbial community of activated sludge (AS) in wastewater treatment plants (WWTP), both in terms of species composition and their abundance. Therefore, it is of interest to elucidate the route of immigrating bacteria into the biological tanks, including the effect of primary settlers. These are commonly used pretreatment units that can possibly selectively increase or reduce the relative abundance of certain bacteria. Species-level identification of the microbial composition of influent wastewater before and after primary settling was carried out in four full-scale municipal WWTPs biweekly over one year by 16S rRNA gene amplicon sequencing. Overall, 37-49% of incoming COD was removed in the primary settlers. Most genera and species were present in the wastewater to all four plants and the trend of these were investigated across the primary settlers. Approximately 50% of the genera had the same trend across at least three WWTPs. Few genera significantly increased in relative read abundance (3.7%) after settling, while 22.3% showed a significant reduction in relative abundance. We investigated process-critical species in AS, such as known nitrifiers, polyphosphate-accumulating organisms, and filamentous bacteria. Most taxa were affected similarly in all WWTPs including multiple genera involved in bulking in AS. However, some genera, e.g., important polyphosphate-accumulating bacteria, had inconsistent trends across WWTPs, suggesting that the characteristics of the wastewater are important for the trend of some bacteria through primary settling. In all cases, primary settling changed the microbial community of the influent wastewater, posing an obvious candidate for upstream control to optimize the assembly of the microbial communities in activated sludge.

Genetic potential for exopolysaccharide synthesis in activated sludge bacteria uncovered by genome-resolved metagenomics.

A good floc formation of activated sludge (AS) is crucial for solid-liquid separation and production of clean effluent during wastewater treatment. Floc formation is partly controlled by self-produced extracellular polymeric substances (EPS) such as exopolysaccharides, proteins, and nucleic acids. Little is known about the composition, structure, and function of EPS in AS and which bacteria produce them. To address this knowledge gap for the exopolysaccharides, we took advantage of 1083 high-quality metagenome-assembled genomes (MAGs) obtained from 23 Danish wastewater treatment plants. We investigated the genomic potential for exopolysaccharide biosynthesis in bacterial species typical in AS systems based on genome mining and gene synteny analyses. Putative gene clusters associated with the biosynthesis of alginate, cellulose, curdlan, diutan, hyaluronic acids, Pel, poly-ß-1,6-N-acetyl-d-glucosamine (PNAG), Psl, S88 capsular polysaccharide, salecan, succinoglycan, and xanthan were identified and linked to individual MAGs, providing a comprehensive overview of the genome-resolved potential for these exopolysaccharides in AS bacteria. The approach and results provide a starting point for a more comprehensive understanding of EPS composition in wastewater treatment systems, which may facilitate a more refined regulation of the activated sludge process for improved stability.

Impact of substrate moisture content on growth and metabolic performance of black soldier fly larvae.

Substrate moisture content is an important but not well-understood variable in production and waste reduction processes that involves black soldier fly (BSF) larvae. The purpose of this paper is to characterise growth and metabolic performance of BSF larvae on substrate moisture contents from 45 to 85%. Larvae developed into prepupae only at 45-75% substrate moisture content. Within this interval, the maximal specific growth rate was highest (0.73 day-1), the growth period shortest (13 days), and the maximal dry weight lowest (88 mg) at 45% moisture content. Differences in cost of growth and maintenance were not observed at the different substrate moisture contents, and differences in larval performance were likely associated to differences in co-occurring microbial activities. As much as 22% of the substrate carbon was emitted as CO2 at 45% moisture content by microorganisms, measured as the difference between total respiration and larval respiration, whereas microbial CO2 production amounted to only 3% of the substrate carbon at 75% moisture content. As consequence of the high specific growth rate and short growth phase, the overall net growth efficiency was higher at 45% moisture content (0.62) than at 75% moisture content (0.52). Overall, the metabolic performance of the BSF larvae was insensitive to differences in substrate moisture content. Their performance was, however indirectly affected by the substrate moisture content due to differences in co-occurring microbial processes in the substrate.

The effects of different potato dextrose agar media on secondary metabolite production in Fusarium.

Potatoes contain several nutrients essential for fungal growth, making them an excellent component of media such as the popular Potato Dextrose Agar (PDA) medium. Commercially, PDA is available from multiple retailers offering virtually the same product. These media, however, could contain small differences in composition of nutrients affecting the expression of secondary metabolites. This study aims to investigate the use of four PDA media from different manufacturers (Fluka, Oxoid, Sigma, and VWR) and their effect on the metabolite profile of four species of Fusarium (F. fujikuroi, F. graminearum, F. pseudograminearum and F. avenaceum). Secondary metabolites were analysed using HPLC-HRMS, from which statistically significant differences in intensities were observed for 9 out of 10 metabolites.