Enterococci as Dominant Xylose Utilizing Lactic Acid Bacteria in Eri Silkworm Midgut and the Potential Use of Enterococcus hirae as Probiotic for Eri Culture

Abstract

A total of 51 pentose utilizing lactic acid bacteria (LAB) were isolated from acid-forming bacteria in the midgut of healthy mature Eri silkworm using de Man, Rogosa and Sharpe (MRS) agar containing 10 g/L xylose (MRS-xylose) as the carbon source supplemented with 0.04% (w/v) bromocresol purple. Further analysis of 16S rRNA gene sequences revealed the highest prevalence of up to 35 enterococci isolates, which included 20 isolates of Enterococcus mundtii, followed by Entercoccus faecalis (eight isolates), Weissella cibaria (four isolates), Enterococcus hirae (two isolates), Enterococcus lactis (one isolate), and Enterococcus faecium (one isolate). All 51 LAB isolates showed positive growth on MRS containing a range of polysaccharides as the sole carbon source. All isolates were able to grow and form clear zones on MRS supplemented with 1 g/L xylose, while E. faecalis SC1, E. faecalis SCT2, and E. hirae SX2 showed tannin tolerance ability up to 5 g/L. Moreover, five isolates showed antimicrobial activity against Eri silkworm pathogens, including Bacillus cereus, Staphylococcus aureus, and Proteus vulgaris, with E. hirae SX2 having the highest inhibitory effect. Supplementation of live E. hirae SX2 on castor leaves significantly improved the weight and reduced the silkworm mortality when compared with the control group (p < 0.05). This cocci LAB can be considered as the new probiotic for Eri culture. Additionally, this finding presented the perspective of non-mulberry silkworm that could also be used as the model for further applying to new trends of the sericulture industry.

Characterization of bacterial diversity and screening of cellulose-degrading bacteria in the gut system of Glenea cantor (Fabricius) larvae

“…Additionally, Lactococcus and Enterococcus were the two most abundant of larval gut samples. Some cellulolytic Enterococcus strains were found in the eri silkworm larvae, Samia ricini ( MsangoSoko et al, 2021 ; Unban et al, 2022 ), since Enterobacteriales have been observed to assist in the breakdown of plant cell wall compounds, including pectin ( Shil et al, 2014 ; Blankenchip et al, 2018 ). Therefore, Enterococcus may have more important role in cellulose degradation in G. cantor ( Robert and Bernalier-Donadille, 2003 ).…”

Sugarcane Wax Metabolites and Their Toxicity to Silkworms

“…Enterococcus is a kind of bacteria that specially intergrowth the gut of silkworm and has the function like synthesizing amino acids [ 17 ], and suppresses sucrose-induced hyperglycemia [ 18 ]. Meanwhile, the genus has antimicrobial activity [ 16 ], and its abundance will also could be affected by other harmful bacterial infections [ 44 ]. Therefore, the increased abundance of Enterococcus in our result might indicate an immune response to wax feeding of silkworm.…”

“…To assess the anti-insect effect of sugarcane wax, setting up a feeding experiment with a model animal is a convenient and effective method. The silkworm ( Bombyx mori ) is a promising model animal for assessing health safety and environmental pollutants in many studies [ 16 , 17 , 18 , 19 , 20 , 21 ], and it can be an alternative to sugarcane borer ( Diatraea sacharalis ) in feeding trail experiments based on the following reasons. First, the silkworm and sugarcane borer are members of the same order (Lepidoptera) and the silkworm is sensitive to chemical compounds such as pesticides, drugs and heavy metals [ 22 ].…”

“…First, the silkworm and sugarcane borer are members of the same order (Lepidoptera) and the silkworm is sensitive to chemical compounds such as pesticides, drugs and heavy metals [ 22 ]. Furthermore, the silkworm has been used as a material in many previous studies that have focused on the investigation of the microbial communities in guts with newly developed sequencing technologies [ 16 , 17 , 18 , 19 , 20 , 21 ]. It was clear that gut-inhabiting microorganisms play an important role in the host’s health, with impacts ranging from improving host metabolism to shaping the immune system [ 23 , 24 , 25 ].…”

Effects of Microbial Transfer during Food-Gut-Feces Circulation on the Health of Bombyx mori

“…S6b), but it is an important human pathogen that causes various diseases, has strong drug resistance, and can survive under harsh conditions ( 41 ). In silkworms, it is often the dominant strain ( 42 – 44 ). Inoculation of silkworm larvae with E. mundtii may have a negative impact on the host response to chlorpyrifos ( 45 ).…”