Abstract
As important pests, scarab beetle larvae survive on plant biomass and the microbiota of the fermentation chamber play an important role in the digestion of lignocellulose-rich diets. However, the cultivable microbes, especially the anaerobic cultivable microbes, are still largely unknown. Here, both cultivable anaerobic and aerobic bacterial communities associated with the fermentation chamber of Holotrichia parallela larvae were investigated. In total bacteria cells directly enumerated by the 4’, 6-diamidino-2-phenylindole (DAPI) staining method, the viable plate counts of cultivable bacteria in the fermentation chamber accounted for 0.92% of proportion. These cultivable bacteria were prone to attach to the fermentation chamber wall (88.41%) compared to the chamber contents. Anaerobic bacteria were dominant in the cultivable bacteria attaching to the fermentation chamber wall (70.20%), while the quantities of anaerobes and aerobes were similar in the chamber contents. Polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE), fingerprinting and sequence analysis of isolated colonies revealed that the cultivable bacteria are affiliated with class γ-Proteobacteria, Bacteroidia, Actinobacteria, Clostridia and β-Proteobacteria. γ-Proteobacteria was the major type of anaerobic cultivable bacteria and even the only one type of aerobic cultivable bacteria. Taken together, our results suggest, for the first time, that anaerobic microbiota are dominant in cultivable bacteria in the special anoxia niche of the fermentation chamber from H. parallela larvae. These bacterial isolates could be a treasure trove for screening lignocellulytic microbes which are essential for the plant biomass digestion of this scarab species.
Highlights
Most living organisms, especially insects, have developed a symbiotic relationship with microorganisms
The number of cultivable bacteria from the Wall Group (WG) samples (12.35×107 cfu/gut) was 4.09 times larger than the Content Group (CG) samples (3.02×107 cfu/gut). This indicated that the cultivable bacteria in the larval fermentation chamber were more apt to adhere to the chamber wall
The present results demonstrated that only 0.92% of the total bacteria in the fermentation chamber of H. parallela could be cultivated, which is similar to the conclusions of Ward et al Fig 5
Summary
Especially insects, have developed a symbiotic relationship with microorganisms. Scarab beetle (Scarabaeidae) larvae are prevailing pests of grassland and farm soils. They can decay the plant materials, including roots and other low nutritional organic matter [10]. These lignocellulose-rich diets are digested in the scarab beetle’s distinctive intestinal tract typically by lignocellulytic degradation in the hindgut with pretreatment in the alkaline midgut by the solubilizing part of the lignocellulosic materials [11]. Several previous studies revealed that the alimentary tract of scarab beetles contains a dense population of flagellate protozoa and bacteria, and some of these microbes can decompose plant fibers, which are likely involved in the digestion of these herbivorous hosts [12,13,14]
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