High-continuity genome assembly of the jellyfish Chrysaora quinquecirrha

DEAR EDITOR,The Atlantic sea nettle(Chrysaora quinquecirrha)has an important evolutionary position due to its high ecological value.However,due to limited sequencing technologies and complex jellyfish genomic sequences,the current C.quinquecirrha genome assembly is highly fragmented.Here,we used the most advanced high-throughput chromosome conformation capture(Hi-C)technology to obtain high-coverage sequencing data of the C.quinquecirrha genome.We then anchored these data to the previously published contig-level assembly to improve the genome.Finally,a high-continuity genome sequence of C.quinquecirrha was successfully assembled,which contained 1882 scaffolds with a N50 length of 3.83 Mb.The N50 length of the genome assembly was 5.23 times longer than the previously released one,and additional analysis revealed that it had a high degree of genomic continuity and accuracy.Acquisition of the high-continuity genome sequence of C.quinquecirrha not only provides a basis for the study of jellyfish evolution through comparative genomics but also provides an important resource for studies on jellyfish growth and development.

Selective and stable elimination of endosymbionts from multiple-infected whitefly Bemisia tabaci by feeding on a cotton plant cultured in antibiotic solutions

The maternally heritable endosymbiont provides many ecosystem functions.Antibiotic elimination of a specific symbiont and establishment of experimental host lines lacking certain symbionts enable the roles of a given symbiont to be explored.The whitefly Bemisia tabaci(Gennadius)in China harbors obligate symbiont Portiera infecting each in-dividual,as well as facultative symbionts,such as Hamiltonella,Rickettsia and Cardinium,with co-infections occurring relatively frequently.So far no studies have evaluated the selectivity and efficacy of a specific symbiont elimination using antibiotics in whiteflies co-infected with different symbionts.Furthermore,no success has been achieved in estab-lishing certain symbiont-free B.tabaci lines.In this study,we treated Hamiltonella infected B.tabaci line,Hamiltonella-Rickettsia-co infected line and Hamiltonella-Cardinium co-infected line by feeding B.tabaci adults with cotton plants cultured in water containing ri-fampicin,ampicillin or a mixture of them,aiming to selectively curing symbiont infections and establishing stable symbiont-free lines.We found ampicillin selectively eliminated Cardinium without afecting Portiera,Hamiltonella and Rickettsia,although they coex-isted in the same host body.Meanwhile,all of the symbionts considered in our study can be removed by rifampicin.The reduction of facultative symbionts occurred at a much quicker pace than obligate symbiont Portiera during rifampicin treatment.Also,we measured the stability of symbiont elimination in whitefly successive generations and established Rickettsia-infected and Cardinium-infected lines which are absent in natural populations.Our results provide new protocols for selective elimination of symbionts co-existing in a host and establishment of different symbiont-infected host lines.