In this study, we investigated whether HK LS 189 supplementation affects pigs’ growth performance and microbiota. In our experiment, when pigs were fed HK LS 189, the growth performance was reduced compared to the control group. Next, the microbiota analysis did not show a significant difference in alpha-diversity, but the beta-diversity analysis did show a significant difference. As a result of microbiota composition analysis, three phyla (Firmicutes, Bacteroidetes, and Proteobacteria) at the phylum level showed abundances of 97.7% and 87.2% in the control group and HK LS 189 group, respectively. Additionally, only Lentisphaerae and Cyanobacteria, which account for rare abundances, showed significant differences between the two groups. At the genus level, there were significant differences in 15 genera; in particular, the relative abundance of Prevotella showed the most significant difference between the two groups. In Prevotella, it was found that the control group accounted for 17.56% more than the HK LS 189 group.
Supplementation with Lactobacillus species promotes mucus secretion in the small intestine and helps the growth of intestinal microorganisms. In fact, L. salivarius is a potential probiotic reported to have the ability to enhance the immune system, attenuate intestinal inflammation, and exert antibacterial activity against pathogenic bacteria, among other effects to date (Alard et al. 2016; Lee et al. 2020; Pothuraju and Sharma 2018). Despite the positive effects of probiotics, including L. salivarius, nonviable microbial cells may have safety benefits over probiotics because they decrease the risk to the host of an imbalanced or compromised immune system. For this reason, recent studies on postbiotics have been actively conducted. Studies have been reported on the differences in the effects of live cells and heat-killed cells on immune function and the intestinal environment, respectively (Jang et al. 2018; Sugahara et al. 2017). Our experimental results provided a different aspect from the results of a previous study. Contrary to the results of earlier studies in pigs, HK LS 189 supplementation decreased the growth performance in this study. As such, the L. salivarius strain used in our study may also have a function similar to that of various probiotics with anti-obesity effects. Although it was not a study on pigs, a recently published paper showed that supplementation of L. salivarius to mice had an anti-obesity effect. Liang et al. (Liang et al. 2021) explained that L. salivarius exhibits an anti-obesity effect by inhibiting food intake and causing changes in gut microbiota by promoting peptide YY secretion. In this study, although we did not elucidate the specific mechanism of the anti-obesity effect exhibited by HK LS 189 supplementation, gut microbiota analysis revealed that HK LS 189 supplementation had an apparent effect on the regulation of gut microbiota in pigs.
A high proportion of Prevotella in the gut microbiota is associated with various metabolic diseases, such as obesity, insulin resistance in nondiabetic people, hypertension, and nonalcoholic fatty liver disease. In particular, some studies have found a positive correlation between the proportion of Prevotella and obesity (León-Mimila et al. 2018; Moreno-Indias et al. 2016). In addition, a recent study reported that Prevotella copri promotes fat accumulation in pigs fed formula diets (Chen et al. 2021). Similar to previous studies, we confirmed that the abundance of Prevotella was significantly reduced in the HK LS 189 group compared to the control group. At the same time, the growth performance was reduced compared to the control group. Among the genera, Parabacteroides was significantly increased in the HK LS 189 group compared to the control group. Parabacteroides, such as Prevotella, have also been associated with obesity in some studies. In particular, Parabacteroides goldsteinii and Parabacteroides distasonis showed anti-obesity effects when they were predominant in the intestine (Wu et al. 2019) and alleviated pathogenesis by an anti-inflammatory response through gut microbiota modulation (Lai et al. 2021). At the genus level, we found that HK LS 189 supplementation caused the significant enrichment of Bacteroidota, Bacteroidia, and Bacteroidales belonging to the Bacteroidetes phylum through LEfSe analysis. It is generally accepted that obesity is accompanied by a decrease in Bacteroidetes (Ley et al. 2006; Pérez-Matute et al. 2015). These findings suggest that HK LS 189 supplementation influenced gut microbiota. The proportion of Prevotella decreased, and the proportion of Parabacteroides and Bacteroidetes increased, resulting in reduced growth performance.
Finally, our PICRUSt analyses revealed that HK LS 189 supplementation also adjusted the metabolic functions of the gut microbiota. The HK LS 189 group was enriched in several KEGG pathways, including signal transduction, the excretory system, metabolism, and lipid metabolism. The alteration of microbial composition is always accompanied by significant functional modification. In a past study, the most common postbiotics were short-chain fatty acids (SCFAs), namely, acetate, propionate, and butyrate, as well as peptides, enzymes, teichoic acids, and vitamins. Among the factors mentioned above, SCFAs induce thermogenesis in brown adipose tissue and browning in white adipose tissue, so they can be used as candidates for preventing and treating obesity (Li et al. 2018). Our experimental results showed that HK LS 189 supplementation could increase the abundance of metabolism and lipid metabolism pathways, which are associated with anti-obesity effects (Li et al. 2020; Wu et al. 2020). Therefore, it is thought that the regulatory action on lipid metabolism of SCFAs derived from L. salivarius was shown to have a preventive effect on obesity. These L. salivarius-mediated changes in functional pathways further support our results that HK LS 189 supplementation can coordinate the gut microbiota and anti-obesity effects in pigs.