ISOLATION AND IDENTIFICATION OF THE á-PROTOBACTERIA

TRANCHIDA M. C.; RICCILLO P.M.; MICIELI M. V.; GARCÍA J.J.

Brasilia DF. Brasil

Simposio; X Simposio de Controle Biológico; 2007

EMBRAPA

Culex pipiens (L.) is a very important vector of human and domestic animal diseases, such as filariasis and West Nile Virus. This species breed in stagnated water with high level of organic matter. A survey for pathogen of Cx. pipiens larvae was conducted in drainage ditches in suburban areas of La Plata, Buenos Aires Province, Argentina, from 2003 to 2006. Culex pipiens larvae with white opaque color were found in several field collections. When the white larvae were dissected and observed in wet mount preparations under a phase contrast microscope presence of bacteria into the hemocoel was recorded.  The majority of infected larvae with such sintomatology died in IV instar. Taxonomic status of the intrahemocelic bacteria was determined by molecular techniques. Bacterial DNA extraction from the hemocoel of infected larvae, PCR amplification, and sequencing of the 16S rRNA gen (rDNA) were conducted using standard techniques. The sequences obtained were compared with 16S rRNA sequence available at the National Center for Biotechnology Information database by BLAST search. BLAST search of the complete 16S rDNA sequence showed that the isolate has a highest level of sequence similarity to Aquaspirillum itersonii  niponicum (92 %) from the a-subclass of Proteobacteria. This bacteria was cultured and isolated on agar rich tryptone medium. Culex pipiens larvae exposed to a large bacteria suspension from axenic culture were not infected excepted for the exposed larvae that presented tegument injuries which became 100% infected and similar aspect than the field collected infected larvae. This result suggested that transmission mode is not per ingestion of bacteria. Bacteria belonging to the genus Aquaspirillum are widely distributed in different aquatic environments, although information related to symbiotic relationship of Aquaspirillum spp with aquatic insects is scarce. This is the first record of this genus as pathogen of mosquito larvae.