Comparative genomics of the Erwinia and Enterobacter olive fly endosymbionts

Anne M. Estes,David J. Hearn,Sonia Agrawal,Julie C. Dunning Hotopp,Elizabeth A. Pierson

doi:10.1038/s41598-018-33809-w

Abstract

The pestivorous tephritid olive fly has long been known as a frequent host of the obligately host-associated bacterial endosymbiont, Erwinia dacicola, as well as other facultative endosymbionts. The genomes of Erwinia dacicola and Enterobacter sp. OLF, isolated from a California olive fly, encode the ability to supplement amino acids and vitamins missing from the olive fruit on which the larvae feed. The Enterobacter sp. OLF genome encodes both uricase and ureases, and the Er. dacicola genome encodes an allantoate transport pathway, suggesting that bird feces or recycling the fly’s waste products may be important sources of nitrogen. No homologs to known nitrogenases were identified in either bacterial genome, despite suggestions of their presence from experiments with antibiotic-treated flies. Comparisons between the olive fly endosymbionts and their free-living relatives revealed similar GC composition and genome size. The Er. dacicola genome has fewer genes for amino acid metabolism, cell motility, and carbohydrate transport and metabolism than free-living Erwinia spp. while having more genes for cell division, nucleotide metabolism and replication as well as mobile elements. A 6,696 bp potential lateral gene transfer composed primarily of amino acid synthesis and transport genes was identified that is also observed in Pseudomonas savastanoii pv savastanoii, the causative agent of olive knot disease.

Highlights

Female tephritid flies cause extensive and costly crop damage by ovipositing their eggs into intact fruit still on the tree
Genomic DNA was extracted from bacteria that were isolated from four separate pools of esophageal bulbs from ~1-month-old surface-sterilized olive flies collected in Orville, CA, USA
One pool was discarded that was found to contain Enterobacter DNA based on 16 S rRNA amplification and sequencing from each of the pools

Summary

Introduction

Female tephritid flies cause extensive and costly crop damage by ovipositing their eggs into intact fruit still on the tree. Sterile insect technique has been employed, whereby laboratory-diet-reared, reproductively-sterile, male flies are released to mate with wild females. It has had limited success for the olive fly[3], due in part to the difficulty establishing and maintaining healthy, competitive olive fly laboratory colonies on an artificial diet. Comparisons between diet-fed laboratory colonies and wild flies reveal different bacterial communities associated with the fly[3]. These native microbial communities may aid the wild fly in feeding on unripe olives, conferring resistance to pesticides, or otherwise enhancing the fly’s health. Organism Size (bp) Number of scaffolds N50 Maximum scaffold size G + C content (%) Protein coding (%) Coding sequences (CDS) Average CDS size (bp) rRNA operons tRNAs

Methods

Results

Discussion

Conclusion