Yeasts affect tolerance of Drosophila melanogaster to food substrate with high NaCl concentration

Abstract

The ability of model animal species, such as Drosophila melanogaster, to adapt quickly to various adverse conditions has been shown in many experimental evolution studies. It is usually assumed by default that such adaptation is due to changes in the gene pool of the studied population of macroorganisms. At the same time, it is known that microbiome can influence biological processes in macroorganisms. In order to assess the possible impact of microbiome on adaptation, we performed an evolutionary experiment in which some D. melanogaster lines were reared on a food substrate with high NaCl concentration while the others were reared on the standard (favourable) substrate. We evaluated the reproductive efficiency of experimental lines on the high salt substrate three years after the experiment started. Our tests confirmed that the lines reared on the salty substrate became more tolerant to high NaCl concentration. Moreover, we found that pre-inoculation of the high salt medium with homogenized salt-tolerant flies tended to improve reproductive efficiency of naïve flies on this medium (compared to pre-inoculation with homogenized control flies). The analysis of yeast microbiome in fly homogenates revealed significant differences in number and species richness of yeasts between salt-tolerant and control lines. We also found that some individual yeast lines extracted from the salt-tolerant flies improved reproductive efficiency of naïve flies on salty substrate (compared to baker’s yeast and no yeast controls), whereas the effect of the yeast lines extracted from the control flies tended to be smaller. The yeast Starmerella bacillaris extracted from the salt-tolerant flies showed the strongest positive effect. This yeast is abundant in all salt-tolerant lines, and very rare or absent in all control lines. The results are consistent with the hypothesis that some components of the yeast microbiome of D. melanogaster contribute to to flies’ tolerance to food substrate with high NaCl concentration.

Salt concentration in substrate modulates the composition of bacterial and yeast microbiomes of Drosophila melanogaster

“…The diversity and abundance of yeasts in flies tend to increase with the rising salt concentration [Figure 3A, triangles; Table 1]. This is in accordance with previous findings that certain yeast species may help D. melanogaster adapt to elevated salt concentrations [41] .…”

“…This aligns with the observation that, with the increase in salt concentration, the percentage of Acetobacter (which can be beneficial for flies) decreased, while the proportion of lactic acid bacteria (also potentially helpful) first increased (from 0% to 4% NaCl), and then drastically decreased at 7% NaCl. It is also in line with the presence of Starmerella yeasts in the fly microbiome at high NaCl concentrations, previously shown to help flies survive and reproduce on the salty substrate [ 42 , 44 ] . These yeasts may also assist the flies in resisting potentially pathogenic bacteria, such as Leuconostoc and Providencia , whose percentage increased at higher salinity.…”

“…Two lines labeled 7a and 7b were reared on a 4% NaCl medium until 2016, and then the salt concentration was increased by 0.5% every 2-3 months until it reached 7%. After that, 7a and 7b lines reared on medium with 7% NaCl medium as described previously [41,43,47] . The fly lines were reared in cylindrical glass jars 0.25 L (0c, 2a-2c, and 4a-4c) or population cages 165 mm × 165 mm × 250 mm (0a-0b, 7a-7b) with medium and water.…”

“…Previous studies have demonstrated that the abundance and species composition of yeasts associated with D. melanogaster may depend on the salt concentration in the substrate. Certain yeast species, such as S. bacillaris, may contribute to the adaptation of laboratory fly lines to salty substrates [41][42][43][44] . Evidently, the yeast community of flies adapts to the salty substrate alongside the host organism, reflecting the adaptability of the entire symbiotic complex.…”

Preference and detrimental effects of high fat, sugar, and salt diet in wild‐caught Drosophila simulans are reversed by flight exercise

“…Previous studies have shown that feeding a high‐fat diet (adding coconut oil, for example) to flies 60,61 or high‐sugar supplementations 62,63 to model T2D and insulin resistance, elicits an obese phenotype with decreased lifespan and fecundity, elevated triglycerides and reduced cardiac function 8,15,64‐66 . The effect of sodium chloride in Drosophila has mostly been studied in the context of salt stress and taste perception, with concentrations above 2% shown to negatively impact fly survival and concentrations higher than 4% proving fatal to both larvae and adults 17‐19,21,67 . Interestingly, we observed significant sexual dimorphism in responses of flies to different diets.…”