Asaia paratransgenesis in mosquitoes

Bacteria of the genus Asaia (Family Acetobacteraceae) were described for the first time twenty years ago with the identification and isolation of Asaia bogorensis from Indonesian flowers of orchid tree (Bauhinia purpurea), plumbago (Plumbago auriculata) and fermented glutinous rice (Yamada et al., 2000). As other acetic acid bacteria, this anaerobic rod-shaped and peritrichously flagellated bacteria proliferates at low pHs (3.0) and 30 °C is considered its optimal growth temperature. It is able to oxidize acetate and lactate to carbon dioxide and water, and to produce acids from D-glucose, D-fructose, L-sorbose, dulcitol and glycerol (Yamada et al., 2000); it is unable, however, to oxidize ethanol to acetic acid (Crotti et al., 2009). It showed resistance to several antibiotics, including ceftazidime, meropenem, aztreonam, penicillin, and ampicillin (Moore et al., 2002). One year after the first discovery, another species of this genus was isolated from a crown flower (dok rak, Calotropis gigantea) collected in Bangkok, and identified as A. siamensis. (Katsura et al., 2001). The repertoire of isolates largely increased over the years: A. krungthepensis, A. lannaensis, A. platycodi, A. prunellae, A. astilbes and A. spathodeae were included in the species array of this bacterial genus (Yukphan et al., 2005, Suzuki et al., 2010). The majority of the identified species were isolated from specimens of flowers collected in Japan, suggesting that the ecology of Asaia species is not only restricted to tropical regions. Asaia was also found to be associated with wine grapes and, more in general, with industrial processes of wine production. In particular, one study reported the presence of this bacteria in wine grapes cultivated in vineyards located in New South Wales, Australia (Bae et al., 2006) A different study, aimed at defining bacterial populations involved in malolactic fermentation of Spanish Tempranillo wine, identified Asaia as a component of the natural bacterial community of this black grape variety (Ruiz et al., 2010). Within the food industry, due to its strong adhesion ability and propensity to produce resistant biofilms, Asaia has been often recognized as a spoilage contaminant of non-alcoholic, non-carbonated beverages (Moore et al, 2002). Its association with insect species was demonstrated for the first time in the main Asian malaria vector, the mosquito Anopheles stephensi (Favia et al, 2007) and in the hemipteran Scaphoideus titanus, the leafhopper vector of the phytoplasma, the causative agent of the Flavescence Dorée, one of the most relevant diseases of the grapevine (Marzorati et al., 2006).