Presence of specific symbiotic bacteria in flies of the subfamily Tephritinae (Diptera Tephritidae) and their phylogenetic relationships: proposal of 'Candidatus Stammerula tephritidis'

Abstract

The presence of symbiotic bacteria in flies belonging to the subfamily Tephritinae, which predominantly infest the flower heads of composite flowers (Asteraceae), was investigated. Twenty-five species of flies, collected mainly in northern Italy, were examined. The bacteria adhered to the midgut epithelium in a space external to the peritrophic membrane and therefore not in direct contact with the gut contents. Specific, unique and live, but unculturable bacteria were consistently found in the majority of the fly species and their presence was also shown to be persistent in flies reared under microbiologically controlled conditions and devoid of any residual culturable intestinal bacteria. Sequencing of the small subunit rRNA gene from the novel bacteria indicated that they belonged to the family Enterobacteriaceae. Three main strongly supported clades were delineated by phylogenetic trees, the first of which featured a coherent set of sequences displaying gene sequence similarities lower than 96 % compared with recognized taxa. The second and third clades featured cases with higher gene sequence similarities to culturable bacteria, including Erwinia persicina and Ewingella americana, respectively. Relative rate tests were supportive of a fast genetic evolution for the majority of the bacterial symbionts of the subfamily Tephritinae. In agreement with the interpretation suggested in 1929 after pioneering observations made by H. J. Stammer, a symbiotic relationship between the novel bacteria and the tephritid flies is postulated. The origin of this apparently polyphyletic relationship is discussed and a novel candidate organism is proposed for the first clade under the designation 'Candidatus Stammerula tephritidis'.

Acetobacter tropicalisIs a Major Symbiont of the Olive Fruit Fly (Bactrocera oleae)

“…The organs were massively colonized by the GFP-labeled bacterium already at 48 (five adults out of five) and 72 (four adults out of four) h postfeeding. It has been suggested that the peritrophic membrane of B. oleae and closely related insect species may work as a mesh that prevents the passage of bacteria from intestinal lumen to the surface of the epithelium (26). This hypothesis may explain our observations that the majority of A. tropicalis cells were detected within the peritrophic membrane, which was already formed in 4-day-old larvae.…”

“…This hypothesis may explain our observations that the majority of A. tropicalis cells were detected within the peritrophic membrane, which was already formed in 4-day-old larvae. In agreement with this hypothesis, it has also been reported that, in contrast to other Tephritinae, there are no bacteria external to the peritrophic membrane of B. oleae (26). However, the recolonization experiments showed the presence of A. tropicalis in both the gut and Malpighian tubules of the adult flies (Fig.…”

Acetic Acid Bacteria, Newly Emerging Symbionts of Insects

“…cells (13,22). In B. oleae, A. tropicalis was found to be tightly entrapped in a brown gelatinous matrix within the peritrophic membrane (42), confirming that the main site of microbial colonization in B. oleae is the gut lumen inside the peritrophic matrix (48). Also, A. tropicalis, when grown in pure culture in a glass tube without shaking, forms a thick pellicle at the liquid-air interface.…”

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

“…Another relationship of Erwinia-related symbiotic bacteria was described in fruit flies (Diptera: Tephritidae). 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).…”