Yeasts Associated with Culex pipiens and Culex theileri Mosquito Larvae and the Effect of Selected Yeast Strains on the Ontogeny of Culex pipiens

Abstract

The success of mosquitoes in nature has been linked to their microbiota and bacteria in particular. Yet, knowledge on their symbioses with yeasts is lacking. To explore possible associations, culturable yeasts were isolated from wild larvae of Culex pipiens and Culex theileri. These yeasts were classified using restriction fragment length polymorphism (RFLP) analyses and identified by sequencing the D1/D2 region of the 26S rRNA gene. Representative strains of Candida, Cryptococcus, Galactomyces, Hannaella, Meyerozyma, Pichia, Rhodosporidium, Rhodotorula, Trichosporon and Wickerhamomyces were isolated. Our results provide, to our knowledge, the first records of the yeast microbiota from wild mosquito larvae and show that they may harbour potential clinically relevant yeast species, including the well-known opportunistic human pathogen Candida albicans. Also, diminished numbers of yeast isolates originating from adults, compared to larvae, support the hypothesis of microbial reduction/elimination during adult emergence and extend it to include yeasts. In addition, strains of Candida albicans, Candida glabrata, Candida pseudolambica, Cryptococcus gattii, Metschnikowia bicuspidata, Saccharomyces cerevisiae and Wickerhamomyces anomalus were tested as sole feed during a 21-day feeding experiment wherein cumulative larval growth, survival and pupation of Cx. pipiens were recorded. Although most yeasts supported larval growth in a similar manner to the positive control S. cerevisiae strain, the different yeast strains impacted differently on Culex pipiens ontogeny. Notably, survival and pupation of larvae were negatively impacted by a representative strain of the primary pathogen C. gattii - signifying some yeasts to be natural antagonists of mosquitoes.

Mosquitoes can harbour yeasts of clinical significance and contribute to their environmental dissemination

“…Notably, C. parapsilosis was observed as the only fungal species shared between adults and larvae of wild Cx. pipiens from a near‐by pond, thus escaping the microbial reduction/elimination during the development of larvae to adult (Steyn et al ., ). This finding suggests a possible effect of C. parapsilosis on mosquito ontogeny, a role that was already suggested for W. anomalus in beetles (Toki et al ., ).…”

“…that documented the cohabitation of such killer yeasts, as C. parapsilosis , M. guilliermondii , Rhodotorula sp. and W. anomalus in the mosquito (Steyn et al ., ).…”

“…In this context, it would be worth investigating which environmental factors may favour the dissemination of opportunistic pathogens. Interestingly, C. parapsilosis was also recovered also from non‐human sources such as domestic animals (Santin et al ., ) and insects, where it was previously described in the larvae of ants (Ba et al ., ), in the alimentary tract of beetles (Suh et al ., ) and in wild Culex pipiens mosquitoes from South Africa (Steyn et al ., ). Mosquitoes may play an important role in the dissemination of opportunistic pathogens, especially those species whose life cycle is strictly dependent on anthropized environments.…”

Mosquito vector‐associated microbiota: Metabarcoding bacteria and eukaryotic symbionts across habitat types in Thailand endemic for dengue and other arthropod‐borne diseases

“…Recent improvements in the exploration of microscopic organisms through the use of metagenomic PCR (Hugenholtz, Goebel, & Pace, 1998; Liles, Manske, Bintrim, Handelsman, & Goodman, 2003) and next‐generation sequencing (Logares et al., 2012) have allowed more accurate and sensitive documentation of these organisms. Several studies have characterized and compared mosquito bacterial microbiota in natural habitats (Akorli et al., 2016; Buck et al., 2016; Gimonneau et al., 2014; Minard et al., 2012, 2014, 2015; Tchioffo et al., 2015; Yadav et al., 2015; Zouache et al., 2010) but few have characterized eukaryotes and in such cases have targeted fungi (Muturi, Bara, Rooney, & Hansen, 2016; Muturi, Ramirez, Rooney, & Dunlap, 2016; Steyn, Roets, & Botha, 2016). We document mosquito microbiota composition and diversity for vector species Aedes aegypti , Aedes albopictus , and Culex quinquefasciatus across ecologically distinct, yet geographically proximate, habitats in Thailand where many mosquito‐borne diseases circulate.…”

Who is eating fructose within the Aedes albopictus gut microbiota?

“…However, this bacterium remains poorly described in the literature (França et al ., ). In addition to bacteria, mosquitoes also host fungal communities that have been largely underexplored thus far (Steyn et al ., ; Bozic et al ., ; Thongsripong et al ., ; Luis et al ., ). We recently identified a rich and diverse fungal community associated with Ae.…”