Effect of β‐1/3,1/6‐glucan upon immune responses and bacteria in the gut of healthy common carp (Cyprinus carpio)

Abstract

β-glucans are frequently included in the diet of healthy common carp Cyprinus carpio as a pre-emptive measure for combatting disease. In order to study the effect this has on the relationship between the gut bacteria and host immune response, carp were maintained on either a β-glucan free diet or feed containing 0.1% MacroGard ® , a β-1/3, 1/6-glucan, for up to 7 weeks and analysis of innate immune gene expression and molecular analysis of the gut bacteria was performed. The data reveals feeding of MacroGard ® to healthy carp does not induce bactericidal innate immune gene expression in the gut but does appear to alter bacterial species richness that did not have a negative effect on overall health. Analysis of innate immune gene expression within the upper midgut revealed that there were significant changes over time in the expression of Interleukin (il)-1β, inducible nitric oxide synthase (inos), mucin (muc2) and C-reactive protein (crp2). Diet did not affect the number of copies of the bacterial 16s rDNA gene in the gut, used as a as a measure of total bacteria population size. However, PCR-denaturing gradient gel electrophoresis (DGGE) analysis revealed a shift in bacterial species richness with MacroGard feeding. Bactericidal immune gene expression of crp2, muc2 and il-1β was weakly correlated with gut bacteria population size indicating a potentially limited role of these genes in interacting with the gut bacteria in healthy carp in order to maintain gut homeostatic conditions. These findings highlight the importance of considering both host immunity and the microbiome together in order to fully elucidate the effeect of immunomodulants, such as β-glucans, upon gut health.

β-Glucan-Induced Immuno-Modulation: A Role for the Intestinal Microbiota and Short-Chain Fatty Acids in Common Carp

“…Interestingly, analysis of microbiota composition following oral gavage with b-glucans in vivo revealed no alteration of the composition, arguing that a single oral gavage with b-glucans will not alter the composition, but can alter the metabolism. In contrast to other studies investigating the effects of b-glucans on fish microbiota composition, those studies investigated the effect of constant exposure during dietary supplementation (27)(28)(29)(30)(31)(32)(33). Our microbiota sequencing data confirm the presence of bacterial genera commonly associated with b-glucan-fermenting capacity.…”

“…In seabass, a 4-week feeding with β-glucan-enriched diets induced a shift toward more Methylobacterium ( 29 ), whereas in rainbow trout and feral common carp, an 8-week feeding with yeast-derived probiotics rich in β-glucans induced a shift toward more lactic acid bacteria ( 30 , 31 ). Recently, a study investigating the effect of feeding β-glucans for 7 weeks to common carp showed, through DGGE analysis, a possible shift in bacterial species richness alongside a downregulation of il-1b expression ( 32 ). Also, addition of β-glucans to the water could affect the composition of intestinal microbiota, at least of Nile tilapia ( 33 ).…”

Commensal bacteria‐immunity crosstalk shapes mucosal homeostasis in teleost fish

“…155 In zebrafish, studies found that feeding fish diets containing high saponin or soy protein contents can induce significantly increased numbers of granulocytes. 156 Additionally, Harris et al 157 found supplementation of Cyprinus carpio with β-glucan could change bacterial composition in the gut. These results might show potential correlation between granulocytes and fish microbiota.…”

Ornamental fish, Cyprinus carpio , fed with fishmeal replacement Ptecticus tenebrifer and Tenebrio molitor

“…The black soldier fly ( Ptecticus tenebrifer ) and yellow mealworm ( Tenebrio molitor ) have particularly interesting characteristics as they can valorize organic waste, producing proteins, fats and energy that is exploitable for feed (De Marco et al., 2015). Moreover, the presence of β‐glucanase from the midgut of T. molitor (Genta et al., 2009; Zhang et al., 2003) that are immunomodulants improves health through increased resistance against infection (Harris et al., 2020).…”