Biology subjects

Merlin, C.

Publications and source records attributed to Merlin, C..

4 recordsLinked to original sources

bioRxiv2022

Microbiome and resistome dynamics along a sewage-effluent-reservoir continuum underline the role of natural attenuation in effluent receiving reservoirs

This study assessed temporal dynamics of total and antibiotic resistant fecal bacterial indicators and antibiotic resistance genes (ARG) along a sewage-effluent-reservoir continuum, in an experimental system consisting of a sewage-fed membrane-aerated bioreactor (MABR) whose effluent fed a 4500 L polypropylene basin that mimicked an effluent storage reservoir. We applied a multidisciplinary approach that coupled physicochemical analyses, cultivation of total and cefotaxime-resistant E. coli, microbiome (bacterial and eukaryotic) analysis and qPCR/ddPCR quantification of selected ARGs. Total and cefotaxime-resistant E. coli loads dropped by approximately 1.5 log units in both the MABR and the reservoir, but the relative reduction (normalized to 16S rRNA genes) in both E. coli and ARGs was higher in the reservoir. Reservoir microbiomes were significantly different from those in the MABR, and were characterized by temporal shifts and periodic algal (Chlorophyta) blooms that were coupled to oxygen and pH fluctuations. Collectively, the data indicates that the decrease in E. coli and ARGs in the MABR was primarily facilitated by sludge removal, whereas in the reservoir, it was predominantly associated with microbial community shifts. The study highlights the capacity of ecological interactions in mitigating antibiotic resistance in both engineered and natural ecosystems. ImportanceAntibiotic resistance is considered one of the most significant public health predicaments of the 21st century, and there is growing evidence that anthropogenically impacted environments such as those receiving raw and treated sewage can contribute to this phenomenon. In this study, we evaluated the dynamics of total and antibiotic resistant fecal pathogen indicators and antibiotic resistance genes along a sewage-treated wastewater-effluent reservoir continuum, concurrent to evaluation of microbial community composition and physicochemical parameters. Results indicate that both the treatment bioreactor and the effluent storage reservoir removed resistant bacteria and antibiotic resistance encoding genes. However, in the reactor removal was primarily linked to physical processes, whereas in the storage reservoir it appeared to be strongly facilitated by ecological interactions. The study highlights the capacity of aquatic ecosystems to alleviate antibiotic resistance, and suggests that ecological processes in aquatic ecosystems can be harnessed to mitigate antibiotic resistance.

microbiology↗

bioRxiv2022

Weighting of celestial and terrestrial cues in the monarch butterfly central complex

Monarch butterflies rely on external cues for orientation during their annual long-distance migration from Northern US and Canada to Central Mexico. These external cues can be celestial cues, such as the sun or polarized light, which are processed in the internal compass of the brain, termed the central complex (CX). Previous research typically focused on how individual simulated celestial cues are encoded in the butterflys CX. However, in nature, the butterflies perceive several celestial cues at the same time and need to integrate them to effectively use the compound of all cues for orientation. In addition, a recent behavioral study revealed that monarch butterflies can rely on terrestrial cues, such as the panoramic skyline, for orientation and use them in combination with the sun to maintain a directed flight course. How the CX encodes a combination of celestial and terrestrial cues and how they are weighted in the butterflys CX is still unknown. Here, we examined how input neurons of the CX, termed TL neurons, combine celestial and terrestrial information. While recording intracellularly from the neurons, we presented a sun stimulus and polarized light to the butterflies as well as a simulated sun and a panoramic scene simultaneously. Our results show that celestial cues are integrated linearly in these cells, while the combination of the sun and a panoramic skyline did not always follow a linear integration of action potential rates. Interestingly, while the weighting between the sun and polarized light was invariant between individual input neurons, it varied strongly when the sun stimulus and the panoramic skyline were presented simultaneously. Taken together, this dynamic weighting between celestial and terrestrial cues may allow the butterflies to flexibly set their cue preference during navigation.

neuroscience↗

bioRxiv2021

State-dependent egocentric and allocentric heading representation in the monarch butterfly brain

For navigation, animals use a robust internal compass. Compass navigation is especially crucial for long-distance migrating animals like monarch butterflies, which use a sun compass to navigate every fall over 4,000 km to their overwintering sites. The central complex, a brain region equipped with sun-compass neurons, is proposed to control the butterflys heading. Although the activity of central-complex neurons exhibits a locomotor-dependent modulation in many insects, the consequences of such modulations for the coding of heading remain unexplored. Here, we developed tetrode recordings from tethered flying monarch butterflies to reveal how flight modulates heading representation. We found that during flight, heading-direction neurons change their tuning, transforming the central-complex network to function as a global compass. This compass coding is characterized by the dominance of steering feedback and allows for robust heading representation even under unreliable visual scenarios, an ideal strategy for maintaining a migratory heading over enormous distances.

neuroscience↗

bioRxiv2020

Isoform-specific regulation of rhythmic gene expression by alternative polyadenylation

Alternative polyadenylation (APA) generates transcript isoforms with different 3 ends. Differences in polyadenylation sites usage, which have been associated with diseases like cancer, regulate mRNA stability, subcellular localization, and translation. By characterizing APA across the 24-hour day in mouse liver, here we show that rhythmic gene expression occurs largely in an APA isoform-specific manner, and that hundreds of arrhythmically expressed genes surprisingly exhibit a rhythmic APA isoform. The underlying mechanisms comprise isoform-specific post-transcriptional regulation, transcription factor driven expression of specific isoform, co-transcriptional recruitment of RNA binding proteins that regulate mRNA cleavage and polyadenylation, and, to a lesser extent, cell subtype-specific expression. Remarkably, rhythmic expression of specific APA isoforms generates 24-hour rhythms in 3 UTR length, with shorter UTRs in anticipation of the mouse active phase. Taken together, our findings demonstrate that cycling transcriptomes are regulated by APA, and suggest that APA strongly impacts the rhythmic regulation of biological functions.

molecular biology↗