Chironomids’ Relationship with Aeromonas Species

Abstract

Chironomids (Diptera: Chironomidae), also known as non-biting midges, are one of the most abundant groups of insects in aquatic habitats. They undergo a complete metamorphosis of four life stages of which three are aquatic (egg, larva, and pupa), and the adult emerges into the air. Chironomids serve as a natural reservoir of Aeromonas and Vibrio cholerae species. Here, we review existing knowledge about the mutual relations between Aeromonas species and chironomids. Using 454-pyrosequencing of the 16S rRNA gene, we found that the prevalence of Aeromonas species in the insects’ egg masses and larvae was 1.6 and 3.3% of the insects’ endogenous microbiota, respectively. Aeromonas abundance per egg mass remained stable during a 6-month period of bacterial monitoring. Different Aeromonas species were isolated and some demonstrated the ability to degrade the insect’s egg masses and to prevent eggs hatching. Chitinase was identified as the enzyme responsible for the egg mass degradation. Different Aeromonas species isolated from chironomids demonstrated the potential to protect their host from toxic metals. Aeromonas is a causative agent of fish infections. Fish are frequently recorded as feeding on chironomids. Thus, fish might be infected with Aeromonas species via chironomid consumption. Aeromonas strains are also responsible for causing gastroenteritis and wound infections in humans. Different virulence genes were identified in Aeromonas species isolated from chironomids. Chironomids may infest drinking water reservoirs, hence be the source of pathogenic Aeromonas strains in drinking water. Chironomids and Aeromonas species have a complicated mutual relationship.

Wild waterfowl as potential vectors of Vibrio cholerae and Aeromonas species

“…The taxonomy of the genus Aeromonas is complicated, and biochemical tests are not accurate enough for species identification. The recommended way to identify Aeromonas species is using other housekeeping gene sequences such as the rpoD gene that encodes RNA polymerase [3]. This can explain why all earlier studies only identified A. hydrophila, whereas we identified several species.…”

“…Ali et al [23] estimated that between 2008 and 2012, 2.9 million cases of cholera occurred worldwide with 95 000 cases of death. Various Aeromonas species can cause intestinal and extra-intestinal infections in humans [2,3], one of the most common being bacteremia with a death rate between 27.5% and 46%. Waterbird migration across national and intercontinental borders provides a mechanism for global dispersion of bacterial species.…”

“…. To identify Aeromonas species, we sequenced the rpoD gene (RNA polymerase that encodes subunit D) as described previously . All sequences were compared with those available in the GenBank (http://www.ncbi.nlm.nih.gov) databases, using the standard nucleotide–nucleotide BLAST program (BLASTN; http://www.ncbi.nlm.nih.gov), to ascertain their closest relatives.…”

“…To identify Aeromonas species, we sequenced the rpoD gene (RNA polymerase that encodes subunit D) as described previously [3]. All sequences were compared with those available in the GenBank (http://www.ncbi.…”

“…V. cholerae and Aeromonas species have been isolated together from invertebrates such as chironomids [3,4], copepods [5], oysters (Crassostrea brasiliana) [6], aquatic arthropods (Gerris spinolae) [7] and different water reservoirs [5][6][7]. This suggests that V. cholerae and Aeromonas species inhabit the same habitats, although it is unclear what their relationship is in these niches.…”