Effects of Mutualistic Bacteria from Entomopathogenic Nematodes on the Microbial Community Structure in Chilo suppressalis

doi:10.13560/j.cnki.biotech.bull.1985.2025-1150

Abstract

Abstract:

Objective This study clarified pathogenicity of Xenorhabdus nematophila, a mutualistic bacterium from entomopathogenic nematodes, to the larvae of Chilo suppressalis. We analyzed the changes in microbial community structure in larvae caused by this bacterium, in order to reveal their pathogenic mechanisms and provide theoretical basis for the development of new microbial insecticides. Method Two treatments were set: Natural infection by Steinernema carpocapsae (SC group) and microneedle injection of X. nematophila HNS01 (XN group), with physiological saline as the control (CA and CB groups). Using 3rd-instar larvae of C. suppressalis as the object, insecticidal activity was assessed. Larvae tissues from each group were collected for metagenomic sequencing to analyze the microbial community structure and gene function. Result The mortality rates of SC group and XN group against 3rd-instar larvae of C. suppressalis were both 100%, with lethal times of 48 h and 96 h, respectively. Alpha diversity showed that Shannon index of SC group was significantly (P<0.05) lower than that of control group CA. There was no significant change in the Simpson index of four groups. Ace and Chao1 indices of SC group were extremely significantly (P<0.01) higher than CA group. Beta diversity showed that the four groups of samples had both overlapping and separated parts in the coordinate space. In terms of species composition, SC group and XN group had the highest abundance of X. nematophila. LEfSe analysis revealed 19 differences between CA and SC groups, and 8 differences between CB and XN groups. KEGG annotation indicated that SC group and XN group are enriched in pathways such as ABC transporter and two-component system. CAZy annotation indicated that SC and XN groups increased the relative abundances of enzyme genes such as CBM50, GT4, and GT2, while the relative abundances of enzyme genes such as AA3, GH16, and GH31 decreased. The relative abundances of GH22 and GH13 enzyme genes were upregulated in SC group, but downregulated in XN group. Conclusion X. nematophila HNS01 has activity of killing 3rd-instar larvae of C. suppressalis. It successfully colonizes the larvae and dominates the host microbial community, exerting pathogenic effects by enhancing nutrient utilization and environmental adaptation, as well as inhibiting host immune response.

Key words: Chilo suppressalis, mutualistic bacteria from entomopathogenic nematodes, Xenorhabdus nematophila, entomopathogenic nematodes, Steinernema carpocapsae, metagenomics

ZHU Hua-jun, DUAN De-yong, WU Sheng-lian, ZHOU Xiao-ling, FANG yong, HUANG Si-di, LIU Ming-xing, LIU Xu-ning, XU Jun, LIU Yang. Effects of Mutualistic Bacteria from Entomopathogenic Nematodes on the Microbial Community Structure in Chilo suppressalis[J]. Biotechnology Bulletin, 2026, 42(5): 213-221.

Figures/Tables 8

Table 1 Statistical results of sample sequencing data processing

样品 Sample	原始测序数据量 Raw base （G）	质控后的数据量 Clean base （G）	Q20 （%）	Q30 （%）	GC （%）
SC1	15.42	14.46	97.88	94.16	41.88
SC2	13.18	12.86	97.19	92.79	41.66
SC3	12.60	12.33	97.60	93.61	39.63
CA1	13.62	13.40	97.75	94.18	38.71
CA2	11.35	11.12	97.75	94.12	38.60
CA3	12.31	12.12	98.55	95.90	37.53
XN1	14.60	14.39	97.78	94.11	37.45
XN2	12.55	12.33	97.91	94.45	41.44
XN3	15.33	14.91	98.03	94.73	39.92
CB1	12.81	12.59	97.68	93.87	38.38
CB2	13.89	13.66	97.54	93.54	38.17
CB3	12.75	12.51	97.71	93.95	38.95

Table 2 Detection of insecticidal activity of C. suppressalis

处理 Treatment	校正死亡率 Corrected mortality rate （%）
处理 Treatment	24 h	48 h	72 h	96 h
SC	40.65±2.03d	100.00±0.00a	100.00±0.00a	100.00±0.00a
XN	33.33±3.33d	54.81±7.76c	73.06±8.56b	100.00±0.00a

Fig. 1 Alpha diversity analysis of microbial community in C. suppressalisA: Shannon index. B: Simpson index. C: Ace index. D: Chao1 index. * indicated significant difference (P<0.05); ** indicated extremely significant difference (P<0.01)

Fig. 2 Beta diversity analysis of microbial community in C. suppressalisA: PCA index; B: PCoA index

Fig. 3 Relative abundance of microorganisms in C. suppressalisA: Taxonomic composition of microbial communities at the phylum level. B: Taxonomic composition of microbial communities at the species level

Fig. 4 LEfSe analysis of microbial communities in C. suppressalisA: Comparison between control CA and treatment SC. B: Comparison between control CB and treatment XN

Fig. 5 Signaling pathway analysis of microbial communities in C. suppressalisA: KEGG annotations at level 2. B: KEGG annotations at level 3

Fig. 6 Carbohydrate active enzyme analysis of microbial communities in C. suppressalisA: Distribution of CAZy gene at level 1. B: Heatmap of differential functional gene abundance in CAZy at level 2

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