Serotonin modulates insect gut bacterial community homeostasis

AANAT1 regulates insect midgut detoxification through the ROS/CncC pathway

Insecticide resistance has been a problem in both the agricultural pests and vectors. Revealing the detoxification mechanisms may help to better manage insect pests. Here, we showed that arylalkylamine N-acetyltransferase 1 (AANAT1) regulates intestinal detoxification process through modulation of reactive oxygen species (ROS)-activated transcription factors cap"n"collar isoform-C (CncC): muscle aponeurosis fibromatosis (Maf) pathway in both the oriental fruit fly, Bactrocera dorsalis, and the arbovirus vector, Aedes aegypti. Knockout/knockdown of AANAT1 led to accumulation of biogenic amines, which induced a decreased in the gut ROS level. The reduced midgut ROS levels resulted in decreased expression of CncC and Maf, leading to lower expression level of detoxification genes. AANAT1 knockout/knockdown insects were more susceptible to insecticide treatments. Our study reveals that normal functionality of AANAT1 is important for the regulation of gut detoxification pathways, providing insights into the mechanism underlying the gut defense against xenobiotics in metazoans.

Pathogenic diversification of the gut commensal Providencia alcalifaciens via acquisition of a second type III secretion system

Providencia alcalifaciens is a Gram-negative bacterium found in a wide variety of water and land environments and organisms. It has been isolated as part of the gut microbiome of animals and insects, as well as from stool samples of patients with diarrhea. Specific P. alcalifaciens strains encode gene homologs of virulence factors found in other pathogenic members of the same Enterobacterales order, such as Salmonella enterica serovar Typhimurium and Shigella flexneri. Whether these genes are also pathogenic determinants in P. alcalifaciens is not known. Here we have used P. alcalifaciens 205/92, a clinical isolate, with in vitro and in vivo infection models to investigate P. alcalifaciens -host interactions at the cellular level. Our particular focus was the role of two type III secretion systems (T3SS) belonging to the Inv-Mxi/Spa family. T3SS 1b is widespread in Providencia spp. and encoded on the chromosome. T3SS 1a is encoded on a large plasmid that is present in a subset of P. alcalifaciens strains, which are primarily isolates from diarrheal patients. Using a combination of electron and fluorescence microscopy and gentamicin protection assays we show that P. alcalifaciens 205/92 is internalized into eukaryotic cells, rapidly lyses its internalization vacuole and proliferates in the cytosol. This triggers caspase-4 dependent inflammasome responses in gut epithelial cells. The requirement for the T3SS 1a in entry, vacuole lysis and cytosolic proliferation is host-cell type specific, playing a more prominent role in human intestinal epithelial cells as compared to macrophages. In a bovine ligated intestinal loop model, P. alcalifaciens colonizes the intestinal mucosa, inducing mild epithelial damage with negligible fluid accumulation. No overt role for T3SS 1a or T3SS 1b was seen in the calf infection model. However, T3SS 1b was required for the rapid killing of Drosophila melanogaster . We propose that the acquisition of two T3SS by horizontal gene transfer has allowed P. alcalifaciens to diversify its host range, from a highly virulent pathogen of insects to an opportunistic gastrointestinal pathogen of animals.

Distribution analysis of TRH in Bactrocera dorsalis using a CRISPR/Cas9-mediated reporter knock-in strain

Although the study of many genes and their protein products is limited by the availability of high-quality antibodies, this problem could be solved by fusing a tag/reporter to an endogenous gene using a gene-editing approach. The type II bacterial CRISPR/Cas system has been demonstrated to be an efficient gene-targeting technology for many insects, including the oriental fruit fly Bactrocera dorsalis. However, knocking in, an important editing method of the CRISPR/Cas9 system, has lagged in its application in insects. Here, we describe a highly efficient homology-directed genome editing system for B. dorsalis that incorporates coinjection of embryos with Cas9 protein, guide RNA and a short single-stranded oligodeoxynucleotide donor. This one-step procedure generates flies carrying V5 tag (42 bp) in the BdorTRH gene. In insects, as in other invertebrates and in vertebrates, the neuronal tryptophan hydroxylase (TRH) gene encodes the rate-limiting enzyme for serotonin biosynthesis in the central nervous system. Using V5 monoclonal antibody, the distribution of TRH in B. dorsalis at different developmental stages was uncovered. Our results will facilitate the generation of insects carrying precise DNA inserts in endogenous genes and will lay foundation for the investigation of the neural mechanisms underlying the serotonin-mediated behaviour of B. dorsalis.

Lactic acid bacteria modulate the CncC pathway to enhance resistance to β-cypermethrin in the oriental fruit fly

The gut microbiota of insects has been shown to regulate host detoxification enzymes. However, the potential regulatory mechanisms involved remain unknown. Here, we report that gut bacteria increase insecticide resistance by activating the cap "n" collar isoform-C (CncC) pathway through enzymatically generated reactive oxygen species (ROS) in Bactrocera dorsalis. We demonstrated that Enterococcus casseliflavus and Lactococcus lactis, two lactic acid-producing bacteria, increase the resistance of B. dorsalis to β-cypermethrin by regulating cytochrome P450 (P450) enzymes and α-glutathione S-transferase (GST) activities. These gut symbionts also induced the expression of CncC and muscle aponeurosis fibromatosis. BdCncC knockdown led to a decrease in resistance caused by gut bacteria. Ingestion of the ROS scavenger vitamin C in resistant strain affected the expression of BdCncC/BdKeap1/BdMafK, resulting in reduced P450 and GST activity. Furthermore, feeding with E. casseliflavus or L. lactis showed that BdNOX5 increased ROS production, and BdNOX5 knockdown affected the expression of the BdCncC/BdMafK pathway and detoxification genes. Moreover, lactic acid feeding activated the ROS-associated regulation of P450 and GST activity. Collectively, our findings indicate that symbiotic gut bacteria modulate intestinal detoxification pathways by affecting physiological biochemistry, thus providing new insights into the involvement of insect gut microbes in the development of insecticide resistance.

Reactive oxygen species are regulated by immune deficiency and Toll pathways in determining the host specificity of honeybee gut bacteria

Host specificity is observed in gut symbionts of diverse animal lineages. But how hosts maintain symbionts while rejecting their close relatives remains elusive. We use eusocial bees and their codiversified gut bacteria to understand host regulation driving symbiotic specificity. The cross-inoculation of bumblebee Gilliamella induced higher prostaglandin in the honeybee gut, promoting a pronounced host response through immune deficiency (IMD) and Toll pathways. Gene silencing and vitamin C treatments indicate that reactive oxygen species (ROS), not antimicrobial peptides, acts as the effector in inhibiting the non-native strain. Quantitative PCR and RNAi further reveal a regulatory function of the IMD and Toll pathways, in which Relish and dorsal-1 may regulate Dual Oxidase (Duox) for ROS production. Therefore, the honeybee maintains symbiotic specificity by creating a hostile gut environment to exotic bacteria, through differential regulation of its immune system, reflecting a co-opting of existing machinery evolved to combat pathogens.

The evolution and ecology of psilocybin in nature

Fungi produce diverse metabolites that can have antimicrobial, antifungal, antifeedant, or psychoactive properties. Among these metabolites are the tryptamine-derived compounds psilocybin, its precursors, and natural derivatives (collectively referred to as psiloids), which have played significant roles in human society and culture. The high allocation of nitrogen to psiloids in mushrooms, along with evidence of convergent evolution and horizontal transfer of psilocybin genes, suggest they provide a selective benefit to some fungi. However, no precise ecological roles of psilocybin have been experimentally determined. The structural and functional similarities of psiloids to serotonin, an essential neurotransmitter in animals, suggest that they may enhance the fitness of fungi through interference with serotonergic processes. However, other ecological mechanisms of psiloids have been proposed. Here, we review the literature pertinent to psilocybin ecology and propose potential adaptive advantages psiloids may confer to fungi.

The Intestinal Immune Defense System in Insects

Over a long period of evolution, insects have developed unique intestinal defenses against invasion by foreign microorganisms, including physical defenses and immune responses. The physical defenses of the insect gut consist mainly of the peritrophic matrix (PM) and mucus layer, which are the first barriers to pathogens. Gut microbes also prevent the colonization of pathogens. Importantly, the immune-deficiency (Imd) pathways produce antimicrobial peptides to eliminate pathogens; mechanisms related to reactive oxygen species are another important pathway for insect intestinal immunity. The janus kinase/STAT signaling pathway is involved in intestinal immunity by producing bactericidal substances and regulating tissue repair. Melanization can produce many bactericidal active substances into the intestine; meanwhile, there are multiple responses in the intestine to fight against viral and parasitic infections. Furthermore, intestinal stem cells (ISCs) are also indispensable in intestinal immunity. Only the coordinated combination of the intestinal immune defense system and intestinal tissue renewal can effectively defend against pathogenic microorganisms.

The modulatory effects of biogenic amines on male mating performance in Bactrocera dorsalis

In insects, the emergence of mating behavior requires the interplay among sex-determination hierarchy mechanisms that regulate sex-specific differentiation, perception and integration of different sensory cues, and precisely patterned behavioral outputs. Biogenic amines, including octopamine (OA), dopamine (DA), tyramine (TA), serotonin and histamine, have been identified and proposed as putative neurotransmitters, neurohormones and/or neuromodulators in the central nervous system of insects to influence multiple physiologies and behaviors. The current study provides the physiological roles and pharmacology of these biogenic amines in the mating performance of Bactrocera dorsalis. Silencing gene expressions coding for biosynthetic enzymes of DA and serotonin in male flies could decrease mating rates, while OA, TA and histamine had no such effects on mating. Furthermore, injection of DA or the DA receptor antagonist chlorpromazine could affect mating rate, as well as injection of serotonin. Pharmacological treatments with other biogenic amines or their receptor antagonists in male flies have no roles in regulating mating performance. We conclude that DA and its receptors are involved in regulating male mating behaviors in B. dorsalis, while changes in serotonin levels in male flies could also affect mating rates. In the current study, the modulatory effects of these biogenic amines on mating performance were investigated, and these results will be helpful in providing a new strategy for controlling B. dorsalis.