Environmental RNA outperforms eDNA metabarcoding in assessing impact of marine pollution: A chromium-spiked mesocosm test.

Environmental (e)DNA metabarcoding holds great promise for biomonitoring and ecotoxicological applications. However, few studies have compared the performance of eDNA versus eRNA metabarcoding in assessing organismal response to marine pollution, in experimental conditions. Here, we performed a chromium (Cr)-spiked mesocosm experimental test on benthic foraminiferal community to investigate the effects on species diversity by analysing both eDNA and eRNA metabarcoding data across different Cr concentrations in the sediment. Foraminiferal diversity in the eRNA data showed a significant negative correlation with the Cr concentration in the sediment, while a positive response was observed in the eDNA data. The foraminiferal OTUs exhibited a higher turnover rate in eRNA than in the eDNA-derived community. Furthermore, in the eRNA samples, OTUs abundance was significantly affected by the Cr gradient in the sediment (Pseudo-R2 = 0.28, p = 0.05), while no significant trend was observed in the eDNA samples. The correlation between Cr concentration and foraminiferal diversity in eRNA datasets was stronger when the less abundant OTUs (<100 reads) were removed and the analyses were conducted exclusively on OTUs shared between eRNA and eDNA datasets. This indicates the importance of metabarcoding data filtering to capture ecological impacts, in addition to using the putatively active organisms in the eRNA dataset. The comparative analyses on foraminiferal diversity revealed that eRNA-based metabarcoding can better assess the response to heavy metal exposure in presence of subtle concentrations of the pollutant. Furthermore, our results suggest that to unlock the full potential for ecosystem assessment, eDNA and eRNA should be studied in parallel to control for potential sequence artifacts in routine ecosystem surveys.

Monitoring newt communities in urban area using eDNA metabarcoding.

Newts are amphibians commonly present in small ponds or garden pools in urban areas. They are protected in many countries and their presence is monitored through visual observation and/or trapping. However, newts are not easy to spot as they are small, elusive and often hidden at the bottom of water bodies. In recent years, environmental DNA (eDNA) has become a popular tool for detecting newts, with a focus on individual species using qPCR assays. Here, we assess the effectiveness of eDNA metabarcoding compared to conventional visual surveys of newt diversity in 45 ponds within urban areas of Geneva canton, Switzerland. We designed newt-specific mitochondrial 16S rRNA primers, which assign the majority of amplicons to newts, and were able to detect four species known to be present in the region, including the invasive subspecies Lissotriton vulgaris meridionalis, native to the Italian peninsula, that has been introduced in the Geneva area recently. The obtained eDNA results were congruent overall with conventional surveys, confirming the morphological observations in the majority of cases (67%). In 25% of cases, a species was only detected genetically, while in 8% of cases, the observations were not supported by eDNA metabarcoding. Our study confirms the usefulness of eDNA metabarcoding as a tool for the effective and non-invasive monitoring of newt community and suggests its broader use for the survey of newt diversity in urban area at larger scales.

Assessing the effect of mercury pollution on cultured benthic foraminifera community using morphological and eDNA metabarcoding approaches.

Mercury (Hg) is a highly toxic element for living organisms and is known to bioaccumulate and biomagnify. Here, we analyze the response of benthic foraminifera communities cultured in mesocosm and exposed to different concentrations of Hg. Standard morphological analyses and environmental DNA metabarcoding show evidence that Hg pollution has detrimental effects on benthic foraminifera. The molecular analysis provides a more complete view of foraminiferal communities including the soft-walled single-chambered monothalamiids and small-sized hard-shelled rotaliids and textulariids than the morphological one. Among these taxa that are typically overlooked in morphological studies we found potential bioindicators of Hg pollution. The mesocosm approach proves to be an effective method to study benthic foraminiferal responses to various types and concentrations of pollutants over time. This study further supports foraminiferal metabarcoding as a complementary and/or alternative method to standard biomonitoring program based on the morphological identification of species communities.

Sumoylation of Drosophila SU(VAR)3-7 is required for its heterochromatic function.

In Drosophila, SU(VAR)3-7 is an essential heterochromatin component. It is required for proper chromatin condensation, and changing its dose modifies position-effect variegation. Sumoylation is a post-translational modification shown to play a role in diverse biological processes. Here, we demonstrate that sumoylation is essential for proper heterochromatin function in Drosophila through modification of SU(VAR)3-7. Indeed, SU(VAR)3-7 is sumoylated at lysine K839; this modification is required for localization of SU(VAR)3-7 at pericentric heterochromatin, chromosome 4, and telomeres. In addition, sumoylation of SU(VAR)3-7 is a prerequisite for its ability to enhance position-effect variegation. Thus, these results show that the heterochromatic function of SU(VAR)3-7 depends on its own sumoylation, and unveil a role for sumoylation in Drosophila heterochromatin.

Drosophila G9a is a nonessential gene.

Mammalian G9a is a euchromatic histone H3 lysine 9 (H3K9) methyltransferase essential for development. Here, we characterize the Drosophila homolog of G9a, dG9a. We generated a dG9a deletion allele by homologous recombination. Analysis of this allele revealed that, in contrast to recent findings, dG9a is not required for fly viability.

Drosophila SETDB1 is required for chromosome 4 silencing.

Histone H3 lysine 9 (H3K9) methylation is associated with gene repression and heterochromatin formation. In Drosophila, SU(VAR)3-9 is responsible for H3K9 methylation mainly at pericentric heterochromatin. However, the histone methyltransferases responsible for H3K9 methylation at euchromatic sites, telomeres, and at the peculiar Chromosome 4 have not yet been identified. Here, we show that DmSETDB1 is involved in nonpericentric H3K9 methylation. Analysis of two DmSetdb1 alleles generated by homologous recombination, a deletion, and an allele where the 3HA tag is fused to the endogenous DmSetdb1, reveals that this gene is essential for fly viability and that DmSETDB1 localizes mainly at Chromosome 4. It also shows that DmSETDB1 is responsible for some of the H3K9 mono- and dimethyl marks in euchromatin and for H3K9 dimethylation on Chromosome 4. Moreover, DmSETDB1 is required for variegated repression of transgenes inserted on Chromosome 4. This study defines DmSETDB1 as a H3K9 methyltransferase that specifically targets euchromatin and the autosomal Chromosome 4 and shows that it is an essential factor for Chromosome 4 silencing.