Evidence of two lineages of the symbiont ‘Candidatus Erwinia dacicola’ in Italian populations of Bactrocera oleae (Rossi) based on 16S rRNA gene sequences

Abstract

The close association between the olive fly Bactrocera oleae (Rossi) (Diptera: Tephritidae) and bacteria has been known for more than a century. Recently, the presence of a host-specific, hereditary, unculturable symbiotic bacterium, designated 'Candidatus Erwinia dacicola', has been described inside the cephalic organ of the fly, called the oesophageal bulb. In the present study, the 16S rRNA gene sequence variability of 'Ca. E. dacicola' was examined within and between 26 Italian olive fly populations sampled across areas where olive trees occur in the wild and areas where cultivated olive trees have been introduced through history. The bacterial contents of the oesophageal bulbs of 314 olive flies were analysed and a minimum of 781 bp of the 16S rRNA gene was sequenced. The corresponding host fly genotype was assessed by sequencing a 776 bp portion of the mitochondrial genome. Two 'Ca. E. dacicola' haplotypes were found (htA and htB), one being slightly more prevalent than the other (57 %). The two haplotypes did not coexist in the same individuals, as confirmed by cloning. Interestingly, the olive fly populations of the two main Italian islands, Sicily and Sardinia, appeared to be represented exclusively by the htB and htA haplotypes, respectively, while peninsular populations showed both bacterial haplotypes in different proportions. No significant correlation emerged between the two symbiont haplotypes and the 16 host fly haplotypes observed, suggesting evidence for a mixed model of vertical and horizontal transmission of the symbiont during the fly life cycle.

Symbiotic bacteria enable olive flies (Bactrocera oleae) to exploit intractable sources of nitrogen

“…All the obtained sequences assigned the bacterium to the B haplotype – one of two variants previously described based on the 16S rDNA sequence variability (Savio et al . ). Other bacteria reported to inhabit the intestinal tract of olive flies (e.g.…”

The effects of geographic origin and antibiotic treatment on the gut symbiotic communities ofBactrocera oleaepopulations

“…It exists in both intra-and extracellular form (Capuzzo et al, 2005;Estes et al, 2009) and plays an important role in facilitating the development of the olive fruit fly larvae in the hostile phenolic environment of unripe olives (Ben-Yosef et al, 2015) and in the enhancement of nitrogen fixation in adult flies (Ben-Yosef et al, 2014). Candidatus E. dacicola is the predominant species detected in wild B. oleae populations from several geographic regions (Capuzzo et al, 2005;Sacchetti et al, 2008;Estes et al, 2009Estes et al, , 2012Kounatidis et al, 2009;Savio et al, 2011). Providencia sp.…”

Review of the role of gut microbiota in mass rearing of the olive fruit fly,Bactrocera oleae, and its parasitoids

“…(), but additional studies were done since by Savio et al. (), Estes et al. (), and Ben‐Yosef et al.…”

“…Various bacterial species have been reported in association with B. oleae over the years (Table 2). Recent studies have clearly demonstrated that the major symbiont of B. oleae is Candidatus Erwinia dacicola, a non-cultivable c-proteo-bacterium, which is present both intra-and extracellularly (Capuzzo et al, 2005;Estes et al, 2009Estes et al, , 2012Kounatidis et al, 2009;Savio et al, 2012;Ben-Yosef et al, 2014, 2015. In addition to Ca.…”