Debaryomyces hansenii supplementation in low fish meal diets promotes growth,modulates microbiota and enhances intestinal condition in juvenile marine fish

Background The development of a sustainable business model with social acceptance,makes necessary to develop new strategies to guarantee the growth,health,and well-being of farmed animals.Debaryomyces hansenii is a yeast species that can be used as a probiotic in aquaculture due to its capacity to i)promote cell proliferation and differen-tiation,ii)have immunostimulatory effects,iii)modulate gut microbiota,and/or iv)enhance the digestive function.To provide inside into the effects of D.hansenii on juveniles of gilthead seabream(Sparus aurata)condition,we inte-grated the evaluation of the main key performance indicators coupled with the integrative analysis of the intestine condition,through histological and microbiota state,and its transcriptomic profiling.Results After 70 days of a nutritional trial in which a diet with low levels of fishmeal(7%)was supplemented with 1.1%of D.hansenii(17.2×10^(5) CFU),an increase of ca.12%in somatic growth was observed together with an improve-ment in feed conversion in fish fed a yeast-supplemented diet.In terms of intestinal condition,this probiotic modu-lated gut microbiota without affecting the intestine cell organization,whereas an increase in the staining intensity of mucins rich in carboxylated and weakly sulphated glycoconjugates coupled with changes in the affinity for certain lectins were noted in goblet cells.Changes in microbiota were characterized by the reduction in abundance of several groups of Proteobacteria,especially those characterized as opportunistic groups.The microarrays-based transcrip-tomic analysis found 232 differential expressed genes in the anterior-mid intestine of S.aurata,that were mostly related to metabolic,antioxidant,immune,and symbiotic processes.Conclusions Dietary administration of D.hansenii enhanced somatic growth and improved feed efficiency param-eters,results that were coupled to an improvement of intestinal condition as histochemical and transcriptomic tools indicated.This probiotic yeast stimulated host-microbiota interactions without altering the intestinal cell organization nor generating dysbiosis,which demonstrated its safety as a feed additive.At the transcriptomic level,D.hansenii pro-moted metabolic pathways,mainly protein-related,sphingolipid,and thymidylate pathways,in addition to enhance antioxidant-related intestinal mechanisms,and to regulate sentinel immune processes,potentiating the defensive capacity meanwhile maintaining the homeostatic status of the intestine.

Isotopic niche provides an insight into the ecology of a symbiont during its geographic expansion

The study of the recent colonization of a symbiont and its interaction with host communities in new locations is an opportunity to understand how they interact.The use of isotopic ratios in trophic ecology can provide measurements of a species'isotopic niche,as well as knowledge about how the isotopic niches between symbiont and host species overlap.Stable isotope measurements were used to assess the sources of carbon assimilated by the host species(the bivalves Mytilus galloprovincialis and Scrobicularia plana)and their associated symbiont pea crab Afropinnotheres monodi,which occurs within these bivalves'mantle cavities.The mixing model estimates suggest that all of them assimilate carbon from similar sources,particularly from pseudofaeces and particulate organic matter in this symbiotic system based on filter feeding.The symbiotic species occupy comparable trophic levels and its association seems to be commensal or parasitic depending on the duration of such association.The pea crab A.monodi reflects a sex-specific diet,where males are more generalist than the soft females because the latter's habitat is restricted to the host bivalve.The high isotopic overlap between soft females and M.galloprovincialis may reflect a good commensal relationship with the host.