From a cell model to a fish trial: Immunomodulatory effects of heat-killed Lactiplantibacillus plantarum as a functional ingredient in aquafeeds for salmonids

Abstract

Paraprobiotics (dead/inactivated probiotics) are promising candidates in functional feeds to promote growth performance, modulate intestinal microbiota and enhance immune response of fish. During industrial production, fish are exposed to several stressful conditions such as handling, sub-optimal nutrition and diseases that can lead to reduced growth, increased mortalities and large economical losses. Such problems can be mitigated by use of functional feeds, leading to more-sustainable aquaculture and improved animal welfare. Lactiplantibacillus plantarum strain L-137 is a common bacterium found in fermented Southeast Asian dish made from fish and rice. The benefits of its heat-killed form (HK L-137) related to growth performance and immunomodulation have been studied in farmed fish such as Nile Tilapia (Oreochromis niloticus), striped catfish (Pangasianodon hypophthalmus) and bighead catfish (Clarias macrocephalus). To study if such benefits can also be observed in salmonids, we worked both at in vitro level using an intestinal epithelium cell line from rainbow trout (Oncorhynchus mykiss; RTgutGC) stimulated with HK L-137 (Feed LP20™) and at in vivo level with pre-smolt Atlantic salmon (Salmo salar) fed HK L-137 at different inclusion levels (20, 100 and 500 mg of Feed LP20™ kg-1 feed). In RTgutGC, the results showed that the barrier function of the cell monolayer was strengthened along with an increased production of IL-1β and a decreased production of Anxa1, indicating a modulation of the immune response. Interestingly, a similar trend was detected at the in vivo level in distal intestine from fish fed the highest inclusion level of HK L-137. Here, a lower production of Anxa1 was also detected (after a 61-day feeding period) in addition to an increase of total plasma IgM in the same group. Furthermore, the RNA-seq analysis showed that HK L-137 was able to modulate the gene expression of pathways related to molecular function, biological process and cellular component in distal intestine, without compromising fish performance and gut microbiota. Taken together, our study has shown that HK L-137 can modulate physiological response of Atlantic salmon, making fish more robust against stressful conditions during production.

Effect of a Probiotic Preparation Based on Lactic and Propionic Acid Bacteria on the Growth of Young Rainbow Trout Oncorhynchus Mykiss in Aquaculture

“…The percentage of fish with signs of bacterial damage decreases, and their functional status and general resistance increase. It has also been shown that even the use of killed cultures of lactic acid bacteria has an immunomodulatory effect (Rocha et al 2023). In our experiment, we demonstrated the advantage of Extra Trout AST 45/15 with the probiotic supplement compared to the same feed without the supplement in terms of final mass, absolute and average daily mass gain, relative mass gain, mass accumulation coefficient, and SGR in rainbow trout.…”

A High-Fat-Diet-Induced Microbiota Imbalance Correlates with Oxidative Stress and the Inflammatory Response in the Gut of Freshwater Drum (Aplodinotus grunniens)

“…We hypothesize that the reduced abundance of Aquabacterium after HFD feeding may be associated with immune and inflammatory responses in the gut, but more studies are needed to provide evidence. Interestingly, previous studies have shown Arenimonas to be an environmentally relevant microbe, frequently isolated in iron ore and sewage, and have not described adverse effects on fish [ 73 , 74 ]. However, a reduced abundance of Arenimonas in the gut of zebrafish on a high-fat diet with added sea buckthorn was recently found [ 75 ].…”

Beneficial effect of heat-killed Lactiplantibacillus plantarum L-137 on intestinal barrier function of rat small intestinal epithelial cells

“…HK L-137 reduces intestinal epithelial permeability and may enhance intestinal barrier function, but the mechanism of action is largely unknown 28,30,31 . In this study, by using rat small intestinal epithelial IEC-6 cells, we showed for the first time that HK L-137 decreases permeability by activating the ERK pathway and increases www.nature.com/scientificreports/ expression of TJ genes and proteins.…”

“…In addition, HK L-137 has been suggested to enhance intestinal barrier function. For example, it was shown to decrease the permeability of the rainbow trout (Oncorhynchus mykiss) intestinal epithelial cell line (RTgutGC), induce intestinal cell growth by activating gut function in broiler chickens, improve intestinal permeability in obese mouse models of metabolic abnormalities and inflammation, and ameliorate systemic and hepatic inflammation through restoration of the intestinal barrier in humans with overweight 28 – 31 . However, the mechanism by which HK L-137 improves intestinal barrier function is still unclear.…”