Bacterial communities associated with culex mosquito larvae and two emergent aquatic plants of bioremediation importance

Abstract

Microbes are important for mosquito nutrition, growth, reproduction and control. In this study, we examined bacterial communities associated with larval mosquitoes and their habitats. Specifically, we characterized bacterial communities associated with late larval instars of the western encephalitis mosquito (Culextarsalis), the submerged portions of two emergent macrophytes (California bulrush, Schoenoplectuscalifornicus and alkali bulrush, Schoenoplectusmaritimus), and the associated water columns to investigate potential differential use of resources by mosquitoes in different wetland habitats. Using next-generation sequence data from 16S rRNA gene hypervariable regions, the alpha diversity of mosquito gut microbial communities did not differ between pond mesocosms containing distinct monotypic plants. Proteobacteria, dominated by the genus Thorsellia (Enterobacteriaceae), was the most abundant phylum recovered from C. tarsalis larvae. Approximately 49% of bacterial OTUs found in larval mosquitoes were identical to OTUs recovered from the water column and submerged portions of the two bulrushes. Plant and water samples were similar to one another, both being dominated by Actinobacteria, Bacteroidetes, Cyanobacteria, Proteobacteria and Verrucomicrobia phyla. Overall, the bacterial communities within C. tarsalis larvae were conserved and did not change across sampling dates and between two distinct plant habitats. Although Thorsellia spp. dominated mosquito gut communities, overlap of mosquito gut, plant and water-column OTUs likely reveal the effects of larval feeding. Future research will investigate the role of the key indicator groups of bacteria across the different developmental stages of this mosquito species.

Figure 1. Mosquito and invertebrate predator abundance.

Repeated-measures analysis of variance showed that mean numbers of mosquitoes, Panel A and invertebrate predators (zygopteran predators), Panel B varied significantly (p< 0.05) between mesocosms planted with alkali bulrush and California bulrush. Alkali bulrush significantly harbored more predators and fewer mosquitoes as compared to the California bulrush. The x-axis represented time after the onset of the experiment. Error bars represent the standard error of the mean based on four replicate mesocosms per plant species.

Figure 2. Alpha diversity measures.

Alpha diversity measures based on PD_Whole tree of the bacterial communities from mosquito larvae, water column and leaves. Sequences from mosquito samples are significantly less diverse than sequences from water and plant samples. The x-axis for the phylogenetic diversity of Bacteria communities from leaf samples is offset by 100 sequences for better illustration.

Figure 3. Community similarity of OTU profiles representation.

PCoA plots based on Bray-Curtis distances of OTU profiles mosquitoes, water and leaf samples from mesocosms containing the two bulrushes from the different sampling dates. Panel A shows points colored by DNA source. Panel B shows points colored by the plant present in the mesocosm. Panel C shows points colored by sampling date.

Figure 4. Taxonomic profiling of mosquito-water-plant microbiome profiles.

PCoA plots of weighted UniFrac distances of bacterial communities in mosquitoes, water and leaf samples from mesocosms containing the two bulrushes (alkali and California bulrushes) from the three sampling dates. Panel A shows the OTUs associated with that region on the plot, scaled based on sequence abundance. Panel B shows a PCoA plot based on three DNA sources (mosquitoes, water and plant leaves), Panel C recolors samples of Panel B to highlight two plant species, Panel D recolors the same samples based on the three sample dates.

Figure 5. Overlap of bacterial communities across habitats.

Venn diagram illustrating overlapping of Bacteria OTUs and sequences between mosquito larvae and habitat ( C . tarsalis larvae; habitat = leaves of alkali and California bulrushes; water = water column samples). The first number represents the number of OTUs, while the number in parentheses represents the number of sequences.

Figure 6. Family-level classification of bacterial communities in mosquitoes.

Family-level classification of bacterial communities in C . tarsalis larvae and their relative proportions.