Seasonal dynamics ofChironomus transvaalensispopulations and the microbial community composition of their egg masses

Abstract

Chironomids (Diptera; Chironomidae) are the most abundant insects in freshwater environments and are considered natural reservoirs of Vibrio cholerae. We monitored the annual dynamics of chironomid populations along with their microbiota in order to better understand host–microbiota interactions. Chironomus transvaalensis populations peaked biannually in August and May–June. The composition of the endogenous bacterial communities of their egg masses clustered in two groups according to the sampling periods August–November and May–July. Nevertheless, a core bacterial community (43%) was present in all egg-mass samples. The most abundant phyla were: Proteobacteria, Firmicutes, Cyanobacteria and Bacteroidetes. The abundance of several genera (e.g. Rheinheimera and Pseudomonas) was positively correlated with C. transvaalensis population dynamics, while a predator–prey interaction was observed between the relative abundance of Vibrio OTUs and C. transvaalensis population size. Chironomids are known to tolerate toxic and stress conditions, and our results demonstrated that bacterial genera that may protect the insect under these conditions are present in the egg masses. After hatching, the first larval meal is the gelatinous matrix that surrounds the eggs. This meal contains a probiotic consortium that may protect the larva during its metamorphosis. The results provide important insights into the host–microbe interactions of chironomids.

Changes in Microbiota Composition Along the Metamorphosis Developmental Stages of Chironomus transvaalensis

“…Proteobacteria, Firmicutes, and Bacteroidetes were the dominant phyla in the current study (Figure 3) as well as in previous studies of chironomid egg masses and larvae microbiota composition (Senderovich and Halpern, 2013;Sela and Halpern, 2019). Nevertheless, in the current study, Deinococcus-Thermus was a dominant phylum in the egg masses (Figure 3) and was never described in chironomids before.…”

“…Rheinheimera was one of the core bacteria in the current study and was relatively more abundant in the egg mass stage (Figure 4). Rheinheimera was also previously identified in C. transvaalensis egg mass microbiota (Senderovich and Halpern, 2013;Sela and Halpern, 2019). Species of this genus have biodegradation abilities (Virk et al, 2012).…”

“…Hydrogenophaga was relatively more abundant in the egg mass stage, while Acinetobacter was relatively more abundant in the adult stage. Species of these genera were previously detected in C. transvaalensis egg masses microbiota and were suggested to play a role in protecting the insect from toxic compounds (Ali, 1991;Halpern, 2012, 2013;Sela and Halpern, 2019).…”

“…The primers, 515F and 806R, were synthesized with 5' linker sequences compatible with Access Array primers for Illumina sequencers ( Caporaso et al, 2012 ; Sigma-Aldridge, Israel): CS1_515F: ACACTGACGACATGGTT CTACAGTGCCAGCMGCCGCGGTAA and CS2_806R: TACGGTAGCAGAGACTTGGTCTGGACTACHVGGGTWTC TAAT-3'. PCR amplification was performed as described by Sela and Halpern (2019) . Briefly, amplification was performed using Takara Master Mix (Clontech, Japan) with a final primer concentration of 0.5 ng/μl for each primer.…”

“…To date, few studies were performed on the bacterial communities associated with chironomid egg masses and larvae, and to the best of our knowledge, no data have been published regarding pupa or adult microbiota composition ( Halpern and Senderovich, 2015 ). Rouf and Rigney (1993) , Halpern et al (2007) , and Lotfi et al (2016) studied the egg mass microbiota composition using culturable methods, whereas Sela and Halpern (2019) used Illumina sequencing of the 16S rRNA gene to study the egg mass microbiota composition and dynamics along 1 year of sampling. Two studies ( Senderovich and Halpern, 2012 , 2013 ) examined a few egg mass and larval bacterial community compositions, and using 454-pyrosequencing of the 16S rRNA gene, Senderovich and Halpern (2013) found significant differences between these communities.…”