Biology subjects

Hermansson, M.

Publications and source records attributed to Hermansson, M..

6 recordsLinked to original sources

bioRxiv2021

Disturbance-based management of ecosystem services and disservices in partial nitritation anammox biofilms

The resistance and resilience provided by functional redundancy, a common feature of microbial communities, is not always advantageous. An example is nitrite oxidation in partial nitritation-anammox (PNA) reactors during wastewater treatment, where suppression of nitrite oxidizers like Nitrospira is sought. In these ecosystems, biofilms provide microhabitats with oxygen gradients, allowing the coexistence aerobic and anaerobic bacteria. We designed a disturbance experiment where PNA biofilms treating water from a high rate activated sludge process removing organic matter (mainstream wastewater), were constantly or intermittently exposed to the effluent of anaerobic sewage sludge digestion dewatering (sidestream wastewater), which has been proposed to inhibit nitrite oxidizers. With increasing sidestream exposure we observed decreased abundance, alpha-diversity, functional versatility, and hence functional redundancy, among Nitrospira in the PNA biofilms, while the opposite patterns were observed for anammox bacteria within Brocadia. At the same time, species turnover was observed for the aerobic ammonia-oxidizing Nitrosomonas populations. The different exposure regimens were associated with metagenomic assembled genomes of Nitrosomonas, Nitrospira, and Brocadia, encoding genes related to N-cycling, substrate usage, and osmotic stress response, possibly explaining the three different patterns by niche differentiation. These findings imply that disturbances can be used to manage the functional redundancy of biofilm microbiomes in a desirable direction, which should be considered when designing operational strategies for wastewater treatment.

microbiology↗

bioRxiv2020

Molecular species selectivity of lipid transport creates a mitochondrial sink for di-unsaturated phospholipids

Mitochondria depend on the import of phospholipid precursors for the biosynthesis of the non-bilayer lipids phosphatidylethanolamine (PE) and cardiolipin required for proper function, yet the mechanism of lipid import remains elusive. Pulse labeling yeast with stable isotope-labeled serine followed by mass spectrometry analysis revealed that mitochondria preferentially import di-unsaturated phosphatidylserine (PS) for conversion to PE by the mitochondrial PS decarboxylase Psd1p. Several protein complexes tethering mitochondria to the endomembrane system have been implicated in lipid transport in yeast, including the endoplasmic reticulum (ER)-mitochondrial encounter structure (ERMES), ER-mitochondria complex (EMC) and the vacuole and mitochondria patch (vCLAMP). By limiting the availability of unsaturated phospholipids through overexpression of the glycerol-3-phosphate acyltransferase Sct1p, conditions were created to investigate the mechanism of lipid transfer and the contribution of the tethering complexes in vivo. Under these conditions, inactivation of ERMES components or the vCLAMP component Vps39p exacerbated the lipid phenotype, indicating that ERMES and Vps39 contribute to the mitochondrial sink for unsaturated acyl chains by mediating transfer of di-unsaturated phospholipids. The results support the concept that intermembrane lipid flow is rate-limited by molecular species-dependent lipid efflux from the donor membrane and driven by the lipid species concentration gradient between donor and acceptor membrane.

biochemistry↗

bioRxiv2020

Diversity and gene expression patterns of functional groups in sidestream and mainstream wastewater partial-nitritation anammox biofilms

Partial nitritation-anammox (PNA) is today used for nitrogen removal from highly concentrated wastewater after anaerobic sludge digestion (sidestream). However, implementation of PNA for treatment of municipal wastewater (mainstream), with its lower ammonium concentration and lower temperature is challenging, which might be due to differences in microbial community composition and/or activity. To investigate this, we compared side-by-side sidestream and mainstream PNA biofilms using amplicon sequencing of 16S rDNA and rRNA, hzsB DNA and mRNA, and the genes nxrB, and amoA. The two communities were different to each other with relatively more heterotrophic denitrifying bacteria and less anammox bacteria in the mainstream. With hzsB and nxrB we found microdiversity among Brocadia and Nitrospira, and turnover (taxa replacement) between sidestream and mainstream. However, in both environments Brocadia sapporoensis represented most of the hzsB DNA and mRNA reads, despite the different environmental conditions and nitrogen removal rates. All of those populations present in both sidestream and mainstream had no differences in their 16S rRNA:rDNA ratios, supporting recent findings that rRNA:rDNA ratios are poor indicators of bacterial activity. The observed diversity within functional groups and composition differences between sidestream and mainstream add complexity to our view of PNA communities with possible implication for reactor function.

microbiology↗

bioRxiv2019

A Novel Process Maintaining Glycerophospholipid Homeostasis in Mammalian Cells

Glycerophospholipid (GPL) homeostasis in eukaryotic cells is thought to be maintained via biosynthesis, degradation and acyl chain remodeling. Here we provide evidence for an additional process termed "head-group remodeling" where other GPLs, when in excess, are rapidly converted to phosphatidylcholine and triacylglycerol. Mass spectrometric studies showed the formation of diacylglycerol, but not phosphatidic acid, from the exogenous GPL thus indicating that the first step is catalyzed by a phospholipase C-type enzyme. Consistently, triacylglycerol formation was significantly inhibited by the knock-down of several PLCs, but not phospholipase Ds. Second, we found that each exogenous GPL strongly inhibited the synthesis of the corresponding endogenous GPL class. Based on these and previous data we hypothesize how mammalian cells could coordinate the multiple processes contributing to GPL homeostasis in mammalian cells. In conclusion, this study provides the first evidence that head group remodeling plays an important role in GPL homeostasis in mammalian cells.

biochemistry↗

bioRxiv2018

Biofilm thickness matters: Deterministic assembly of different functions and communities in nitrifying biofilms

Microbial biofilms are important in natural ecosystems and in biotechnological applications. Biofilm architecture influences organisms spatial positions, who their neighbors are, and redox gradients, which in turn determine functions. We ask if and how biofilm thickness influences community composition, architecture and functions. But biofilm thickness cannot easily be isolated from external environmental factors. We designed a metacommunity system in a wastewater treatment plant, where either 50 or 400 {micro}m thick nitrifying biofilms were grown simultaneously on biofilm carriers in the same reactor. Model simulations showed that the 50 {micro}m biofilms could be fully oxygenated whereas the 400 {micro}m biofilms contained anaerobic zones. The 50 and 400 {micro}m biofilms developed significantly different communities. due to deterministic factors were stronger than homogenizing dispersal forces in the reactor, despite the fact that biofilms experienced the same history and external conditions. Relative abundance of aerobic nitrifiers was higher in the 50 {micro}m biofilms, while anaerobic ammonium oxidizers were more abundant in the 400 {micro}m biofilms. However, turnover was larger than the nestedness component of between-group beta-diversity, i.e. the 50 {micro}m biofilm was not just a subset of the thicker 400 {micro}m biofilm with reduced taxa richness. Furthermore, the communities had different nitrogen transformation rates. The study shows that biofilm thickness has a strong impact on community composition and ecosystem function, which has implications for biotechnological applications, and for our general understanding of biofilms.\n\nIMPORTANCEMicroorganisms colonize all surfaces in water and form biofilms. Diffusion limitations form steep gradients of energy and nutrient sources from the water phase into the deeper biofilm parts, influencing community composition through the biofilm. Thickness of the biofilm will affect diffusion gradients, and is therefore presumably important for biofilm composition. Since environmental factors determine thickness, studies of how thickness influences biofilm functions and community assembly, have been difficult to perform. We studied biofilms for wastewater treatment with fixed thicknesses of 50 and 400 {micro}m during otherwise similar conditions and history. Despite growing in the same wastewater reactor, 16S rRNA gene sequencing and confocal microscopy showed the formation of two different communities, performing different ecosystem functions. Using statistical methods, we show for the first time, how biofilm thickness influences community assembly. The results help our understanding of the ecology of microbial biofilms, and in designing engineered systems based on ecological principles.

microbiology↗

bioRxiv2018

Deterministic and stochastic processes influence the reproducibility of microbial community assembly during aerobic granulation

Aerobic granular sludge is an energy efficient and compact biofilm process for wastewater treatment which has received much attention during the last decades and is now being implemented in full-scale. However, the factors involved in microbial community assembly during formation of granules are poorly understood and little is known about the reproducibility in treatment performance and community structure. Here we show that both deterministic and stochastic factors exert a dynamic influence during microbial community assembly into granular sludge. During granulation, the microbial communities in three replicate sequencing batch reactors followed similar successional trajectories of the most abundant taxa and showed similar dynamics in diversity. Deterministic factors dominated the assembly of the most abundant community members as the microbial community transitioned from floccular to granular form. Stochastic factors mostly affected rare members of the communities and caused the microbial community structure to diverge in one of the reactors; however, this did not have an impact on the treatment performance. This demonstrates that the reactor function and the dynamics of the most abundant community members are in fact reproducible during the formation of aerobic granules.

microbiology↗