Gut bacterium Delftia tsuruhatensis strain ALG19 isolated from Agrilus planipennis larvae degrades cellulose in Fraxinus velutina

Yi-Han WANG ¹ Qi LIU ¹ Thi Minh Dien VUONG ² Hua-Ling WANG ^1,3 Jing-Yi FU ¹ Xiao-Yu SU ¹ Ying-Jie WANG ¹ Jia-Yu YANG ¹ Jian-Yong ZENG ^1,4* Hui-Ping LI ^1,3*

• ¹ Hebei Agricultural University, Baoding, China
• ² Modern Educational Technology Center, Hebei Agricultural University, Baoding, China
• ³ Hebei Urban Forest Health Technology Innovation Center, Baoding, China
• ⁴ Hebei Key Laboratory for Tree Genetic Resources and Forest Protection, Baoding, China

Strain ALG19 is a dominant culturable bacterium isolated from the larval gut of emerald ash borer Agrilus planipennis that feeds on velvet ash Fraxinus velutina. Based on the whole-genome sequencing, average nucleotide identity (ANI) and phylogenetic analysis of single-copy orthologous genes suggested that strain ALG19 is Delftia tsuruhatensis. Further gene annotation showed that D. tsuruhatensis ALG19 has 283 genes associated with carbohydrate transport and metabolism in the COG database; 355 genes related to the carbohydrate metabolism pathway were annotated in the KEGG database; and 105 carbohydrate-active genes in CAZy database, indicating the potential to degrade cellulose of D. tsuruhatensis. Subsequently, the hydrolysis circle test confirmed that strain ALG19 can degrade carboxymethyl cellulose, with a hydrolysis circle diameter ratio of 1.74. In a filter paper cellulose degradation test, strain ALG19 completely disintegrated filter paper strips into flocs after being cultured in an inorganic salt medium for 60 days, while the control group basically retained the original shape, and the dry weight of the precipitation was 38.06% less than that of the control group. Furthermore, when cultured in an inorganic salt medium with the extracted phloem cellulose of velvet ash as the sole carbon source for 60 days, ALG19 reduced the cellulose content to 69.91%, which was 15.60% lower than that of the control group (82.83%). This suggests that D. tsuruhatensis ALG19 is capable of breaking down the cellulose present in the host plant of the emerald ash borer, its host insect. The present study provides a potential target microorganism for the future pest management strategies, which could reduce the damage caused by emerald ash borer by weakening its digestive ability.