Trust your guts? The effect of gut section on diet composition and impact of Mus musculus on islands using metabarcoding

1. DNA metabarcoding is widely used to characterize the diet of species, and it becomes very relevant for biodiversity conservation, allowing the understanding of trophic chains and the impact of invasive species. The need for cost‐effective biodiversity monitoring methods fostered advances in this technique. One question that arises is which sample type provides a better diet representation.
2. Therefore, with this study, we intended to evaluate if there were differences in diet estimates according to the section of the gastrointestinal tract analysed and which section(s) provided the best diet representation. Additionally, we intended to infer the ecological/economic impacts of an invader as a model of the potential effects in an originally mammal‐free ecosystem.
3. We examined the gut contents of the house mouse Mus musculus introduced to Cabo Verde, considering three sections: stomach, small intestine, and large intestine. We applied a DNA‐metabarcoding approach using two genetic markers, one specific for plants and another for invertebrates.
4. We showed that this invader consumed 131 taxa (73 plants and 58 invertebrates). We obtained significant differences in the composition of two of the three sections, with a higher incidence of invertebrates in the stomach and plants in the intestines. This may be due to stomach inhibitors acting on plants and/or to faster absorption of soft‐body invertebrates compared to the plant fibers in the intestines. We verified that the impact of this invader in the ecosystem is predominantly negative, as at least 50% of the ingested items were native, endemic, or economically important taxa, and only 19% of the diet items were exotics.
5. Overall, results showed the need to analyse only two gastrointestinal tract sections to obtain robust diet data, increasing the cost‐effectiveness of the method. Furthermore, by uncovering the native taxa most frequently preyed on by mice, this DNA‐metabarcoding approach allowed us to evaluate efficiently which are at the highest risk.

     

Interactions between fungi and bacteria influence microbial community structure in the Megachile rotundata larval gut

Recent declines in bee populations coupled with advances in DNA-sequencing technology have sparked a renaissance in studies of bee-associated microbes. Megachile rotundata is an important field crop pollinator, but is stricken by chalkbrood, a disease caused by the fungus Ascosphaera aggregata. To test the hypothesis that some gut microbes directly or indirectly affect the growth of others, we applied four treatments to the pollen provisions of M. rotundata eggs and young larvae: antibacterials, antifungals, A. aggregata spores and a no-treatment control. We allowed the larvae to develop, and then used 454 pyrosequencing and quantitative PCR (for A. aggregata) to investigate fungal and bacterial communities in the larval gut. Antifungals lowered A. aggregata abundance but increased the diversity of surviving fungi. This suggests that A. aggregata inhibits the growth of other fungi in the gut through chemical or competitive interaction. Bacterial richness decreased under the antifungal treatment, suggesting that changes in the fungal community caused changes in the bacterial community. We found no evidence that bacteria affect fungal communities. Lactobacillus kunkeei clade bacteria were common members of the larval gut microbiota and exhibited antibiotic resistance. Further research is needed to determine the effect of gut microbes on M. rotundata health.     

Glucagon signalling in the dorsal vagal complex is sufficient and necessary for high‐protein feeding to regulate glucose homeostasis in vivo

High‐protein feeding acutely lowers postprandial glucose concentration compared to low‐protein feeding, despite a dichotomous rise of circulating glucagon levels. The physiological role of this glucagon rise has been largely overlooked. We here first report that glucagon signalling in the dorsal vagal complex (DVC) of the brain is sufficient to lower glucose production by activating a Gcgr–PKA–ERK–K_ATP channel signalling cascade in the DVC of rats in vivo. We further demonstrate that direct blockade of DVC Gcgr signalling negates the acute ability of high‐ vs. low‐protein feeding to reduce plasma glucose concentration, indicating that the elevated circulating glucagon during high‐protein feeding acts in the brain to lower plasma glucose levels. These data revise the physiological role of glucagon and argue that brain glucagon signalling contributes to glucose homeostasis during dietary protein intake.     

Analyses of the functional regions of DEAD-box RNA "helicases" with deletion and chimera constructs tested in vivo and in vitro

The DEAD-box family of putative RNA helicases is composed of ubiquitous proteins that are found in nearly all organisms and that are involved in virtually all processes involving RNA. They are characterized by two tandemly linked, RecA-like domains that contain 11 conserved motifs and highly variable amino- and carboxy-terminal flanking sequences. For this reason, they are often considered to be modular multi-domain proteins. We tested this by making extensive BLASTs and sequence alignments to elucidate the minimal functional unit in nature. We then used this information to construct chimeras and deletions of six essential yeast proteins that were assayed in vivo. We purified many of the different constructs and characterized their biochemical properties in vitro. We found that sequence elements can only be switched between closely related proteins and that the carboxy-terminal sequences are important for high ATPase and strand displacement activities and for high RNA binding affinity. The amino-terminal elements were often toxic when overexpressed in vivo, and they may play regulatory roles. Both the amino and the carboxyl regions have a high frequency of sequences that are predicted to be intrinsically disordered, indicating that the flanking regions do not form distinct modular domains but probably assume an ordered structure with ligand binding. Finally, the minimal functional unit of the DEAD-box core starts two amino acids before the isolated phenylalanine of the Q motif and extends to about 35 residues beyond motif VI. These experiments provide evidence for how a highly conserved structural domain can be adapted to different cellular needs.