Dominant egg surface bacteria of Holotrichia oblita (Coleoptera: Scarabaeidae) inhibit the multiplication of Bacillus thuringiensis and Beauveria bassiana

Abstract

Holotrichia oblita (Coleoptera: Scarabaeidae) and some other scarab beetles are the main soil-dwelling pests in China. Bacillus thuringiensis (Bt) and Beauveria bassiana (Bb) are entomopathogens that have been used as biocontrol agents of various pests. However, scarab larvae especially H. oblita exhibited strong adaptability to these pathogens. Compared to other scarabs, H. oblita could form a specific soil egg case (SEC) structure surrounding its eggs, and young larvae complete the initial development process inside this structure. In this study, we investigated the role of SEC structure and microorganisms from SEC and egg surface in pathogen adaptability. 16S rRNA gene analysis revealed low bacterial richness and high community unevenness in egg surface, with Proteobacteria, Firmicutes, Bacteroidetes and Fusobacteria dominating. In terms of OTUs composition analysis, the data show that the egg surface contains a large number of unique bacteria, indicating that the egg bacterial community may be derived from maternal transmission. Furthermore, we found that all culturable bacteria isolated from egg surface possessed antimicrobial activity against both Bt and Bb. The Pseudomonas bacteria with a significantly higher abundance in egg surface showed strong Bt- and Bb antagonistic ability. In conclusion, this study demonstrated a unique and antimicrobial bacterial community of H. oblita egg surface, which may contribute to its adaptability. Furthermore, the specific SEC structure surrounding the H. oblita eggs will provide a stable microenvironment for the eggs and egg surface bacteria, which probably provides more advantages for H. oblita adaptation ability.

Characterization of Microorganisms from Protaetia brevitarsis Larva Frass

“…Bacterial community composition was analyzed by amplicon sequencing of the 16S rRNA gene V4 hypervariable region with the universal primer set 515F/806R [23]. PCR was carried out as follows: initial denaturation at 95 • C for 10 min, 35 cycles at 94 • C for 1 min, 55 • C for 1 min, and 72 • C for 1 min, and final extension at 72 • C for 10 min.…”

Symbiotic Bacteria System of Locusta migratoria Showed Antifungal Capabilities against Beauveria bassiana

“…A stable microbial community is critical for organism health [ 26 ]. The microbial communities on living organisms are always challenged by both invasive [ 21 ] and opportunistic pathogens [ 27 ]. Beauveria bassiana is an invasive species, in contrast to the normal migratory locust microbial community in the microenvironment of the locust.…”

“…The virulence of different strains of the same pathogenic fungi to the same host can sometimes be very different [ 28 ]; just like the results obtained in the LT50 test, the virulence of strain BbZJ1 to locusts was significantly stronger than that of strains BbBJ and BbHN1. Changes in virulence factors in fungi due to gene mutation [ 29 , 30 ] and immune differences among host individuals possibly explain this variation in virulence [ 27 , 31 ]. Previous studies have shown that microbial communities play key roles in the health and development of their multicellular hosts and are an important part of the arthropod immune system [ 27 , 32 ].…”

“…Changes in virulence factors in fungi due to gene mutation [ 29 , 30 ] and immune differences among host individuals possibly explain this variation in virulence [ 27 , 31 ]. Previous studies have shown that microbial communities play key roles in the health and development of their multicellular hosts and are an important part of the arthropod immune system [ 27 , 32 ].…”