‘Candidatus Erwinia dacicola’, a coevolved symbiotic bacterium of the olive fly Bactrocera oleae (Gmelin)

Abstract

The taxonomic identity of the hereditary prokaryotic symbiont of the olive fly Bactrocera oleae (Diptera: Tephritidae) was investigated. In order to avoid superficial microbial contaminants and loosely associated saprophytic biota, flies were surface-sterilized at the larval stage and reared under aseptic conditions until adult emergence. B. oleae flies originating from different geographical locations and collected at different times of the year were tested. Bacterial isolation was undertaken from the cephalic oesophageal bulb, which is known to be a specific site of accumulation for the hosted microsymbionts in the adult insect. Despite evidence of multiplication cycles taking place within the insect, attempts at cultivation of the isolated bacteria ex situ were not productive at any stage, leading to the choice of unculturable status definition. PCR amplification and nucleotide sequencing of the entire 16S rRNA gene consistently yielded a single sequence that displayed marked similarity with enterobacterial lineages, with closest matches (97 %) to Erwinia persicina and Erwinia rhapontici. The novel taxon differs from common intestinal bacterial species of fruit flies and from instances of culturable bacteria previously described in B. oleae raised without sterility precautions, which we also observed as minority occupants or occasional contaminants. The symbiont's identity is also distinct from Pseudomonas savastanoi. In all observations, the numerically dominant inhabitant of the olive fly oesophageal organ was the same unculturable organism, whose presence at later stages was also regularly observed in the midgut. A novel species is proposed, by virtue of its unique properties, under the designation ‘Candidatus Erwinia dacicola’.

Characterization of an Obligate Intracellular Bacterium in the Midgut Epithelium of the Bulrush Bug Chilacis typhae (Heteroptera, Lygaeidae, Artheneinae)

“…Here, the bacteria reside intracellularly in the epithelial cells of digestive tissue in larval stages, as in Chilacis, but also extracellularly in the midgut lumen between the peritrophic tube and the midgut epithelium in adults (15,42). In the olive fly Bactrocera oleae the symbionts were additionally localized in a special cephalic organ (esophageal bulb or pharyngeal bulb) connected to the pharynx (9,10). A recent study indicates that these bacteria have an effect on olive fly fitness and are involved in the nitrogen cycle and/or with supplementation of essential amino acids (7).…”

Give us the tools and we will do the job: symbiotic bacteria affect olive fly fitness in a diet-dependent fashion

“…In adult olive flies, a diverticulum of the oesophagus accommodates a large and proliferating population of extracellular bacteria (Petri 1910;Stammer 1929;Girolami 1973). This organ periodically releases bacteria into the oesophagus, which inoculate and densely colonize the anterior midgut (Petri 1910;Girolami 1973;Capuzzo et al 2005). The association extends via the egg and continues in the larval stage where bacteria heavily populate the four midgut caeca during the entire larval development within the olive fruit (Petri 1910;Stammer 1929;Mazzini & Vita 1981).…”

“…The association extends via the egg and continues in the larval stage where bacteria heavily populate the four midgut caeca during the entire larval development within the olive fruit (Petri 1910;Stammer 1929;Mazzini & Vita 1981). Although recent studies have identified several species of bacteria in the digestive tract of wild olive flies (Kounatidis et al 2009), the most common and widespread of these is Candidatus Erwinia dacicola (Capuzzo et al 2005;Estes 2009;Estes et al 2009). …”

Community Structure of the Mediterranean Fruit Fly Microbiota: Seasonal and Spatial Sources of Variation

“…Most of the data obtained on insect gut bacterial diversity is derived from traditional microbial methods such as viable plate counts and phenetic taxonomy. However, in recent years the use of the rRNA approach enables further characterization of the enteric microbiota of many insects (Egert et al, 2003;Reeson et al, 2003;Dillon and Dillon, 2004;Behar et al, 2005;Capuzzo et al, 2005;Mohr and Tebbe, 2006).…”