FicD genes in invertebrates: A tale of transposons, pathogenic and integrated viruses.

Many gene families are shared across the tree of life between distantly related species because of horizontal gene transfers (HGTs). However, the frequency of HGTs varies strongly between gene families and biotic realms suggesting differential selection pressures and functional bias. One gene family with a wide distribution are FIC-domain containing enzymes (FicDs). FicDs catalyze AMPylation, a post-translational protein modification consisting in the addition of adenosine monophosphate to accessible residues of target proteins. Beside the well-known conservation of FicDs in deuterostomes, we report the presence of a conserved FicD gene ortholog in a large number of protostomes and microbial eukaryotes. We also reported additional FicD gene copies in the genomes of some rotifers, parasitic worms and bivalves. A few dsDNA viruses of these invertebrates, including White spot syndrome virus, Cherax quadricarinatus iridovirus, Ostreid herpesvirus-1 and the beetle nudivirus, carry copies of FicDs, with phylogenetic analysis suggesting a common origin of these FicD copies and the duplicated FicDs of their invertebrate hosts. HGTs and gene duplications possibly mediated by endogenous viruses or genetic mobile elements seem to have contributed to the transfer of AMPylation ability from bacteria and eukaryotes to pathogenic viruses, where this pathway could have been hijacked to promote viral infection.

Impaired reproduction, energy reserves and dysbiosis: The overlooked consequences of heatwaves in a bivalve mollusc.

Extreme events like Marine Heatwaves (MHWs) are becoming more intense, severe, and frequent, threatening benthic communities, specifically bivalves. However, the consequences of non-lethal MHWs on animals are still poorly understood. Here, we exposed the Manila clam Ruditapes philippinarum to non-lethal MHW for 30 days and provided an integrative view of its effects. Our result indicated that albeit non-lethal, MHW reduced clam's energy reserves (by reducing their hepato-somatic index), triggered antioxidant defenses (particularly in males), impaired reproduction (via the production of smaller oocytes in females), triggered dysbiosis in the digestive gland microbiota and altered animals' behaviour (by impacting their burying capacity) and filtration rate. Such effects were seen also at RNA-seq (i.e. many down-regulated genes belonged to reproduction) and metabolome level. Interestingly, negative effects were more pronounced in males than in females. Our results show that MHWs influence animal physiology at multiple levels, likely impacting its fitness and its ecosystem services.

NMR Metabolite Profiles of the Bivalve Mollusc Mytilus galloprovincialis Before and After Immune Stimulation With Vibrio splendidus.

The hemolymph metabolome of Mytilus galloprovincialis injected with live Vibrio splendidus bacteria was analyzed by 1H-NMR spectrometry. Changes in spectral hemolymph profiles were already detected after mussel acclimation (3 days at 18 or 25 °C). A significant decrease of succinic acid was accompanied by an increase of most free amino acids, mytilitol, and, to a smaller degree, osmolytes. These metabolic changes are consistent with effective osmoregulation, and the restart of aerobic respiration after the functional anaerobiosis occurred during transport. The injection of Vibrio splendidus in mussels acclimated at 18°C caused a significant decrease of several amino acids, sugars, and unassigned chemical species, more pronounced at 24 than at 12 h postinjection. Correlation heatmaps indicated dynamic metabolic adjustments and the relevance of protein turnover in maintaining the homeostasis during the response to stressful stimuli. This study confirms NMR-based metabolomics as a feasible analytical approach complementary to other omics techniques in the investigation of the functional mussel responses to environmental challenges.