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

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.

[Correlation of intracranial pressure and diameter of the sheath of the optic nerve by computed tomography in severe traumatic brain injury]. / Korreliatsiia vnutricherepnogo davleniia i diametra obolochki zritel'nogo nerva po dannym komp'iuternoi tomografii pri tiazheloi cherepno-mozgovoi travme.

BACKGROUND: Noninvasive techniques to evaluate intracranial pressure (ICP) are important for everyday practice in intensive care and neurosurgery departments. CT data can be used to evaluate the optic nerve sheath diameter (ONSD) and, indirectly, the ICP value. The ONSD value is an additional criterion in deciding on invasive monitoring of ICP. AIM: To analyze a correlation between CT-based ONSD and the results of invasive measurements of ICP in patients with severe traumatic brain injury. MATERIAL AND METHODS: The study evaluated 41 patients with severe traumatic brain injury within the first 48 h after injury. Invasive monitoring of ICP (Codman & Shurtlett, MA, USA) was performed during 7±1.7 days. ONSD was measured using axial CT scans (CereTom, Neurologica Danvers, MA, USA) with a slice thickness of 2.5 mm. The ONSD value was measured at a distance of 3 mm from the posterior eyeball contour. The patients were allocated in a group with normal ICP (10 patients) and a group with high ICP (31 patients). ONSD served as an ICP classifier. The data were processed using ROC analysis. RESULTS: According to the CT data, the optimal threshold ONSD value was 6.35 mm in patients in the acute TBI period. The sensitivity was 0.93 (95% СI 0.84-1.00), the specificity was 0.80 (95% СI 0.50-1.00), and AUC was 0.87 (95% СI 0.69-1.00). CONCLUSION: We found a correlation between the CT-based ONSD and the median ICP (R=0.32, p<0.05). An ONSD value of 6.35 mm and more is one of the signs of previous or existing ICP.

[Adaptation of Drosophila melanogaster to stressful nutritional conditions leads to the expansion of the trophic niche].

Adaptation to stress factors is often accompanied by negative side effects that are manifested in lower fitness in the absence of the stress factor. This can lead to ecological specialization of the populations adapted to stressful environment and, ultimately, to ecological speciation. However, the existence of eurytopic species with a wide spectrum of ecological tolerance implies that adaptation to marginal conditions apparently can proceed without negative side effects or even involve positive effects, leading to niche expansion. Experimental evidence in favour of this evolutionary scenario is scarce. In the course of the evolutionary experiment that lasted for 20 generations, the laboratory populations of Drosophila melanogaster successfully adapted to stressful media with high NaCl concentration. The adaptation is manifested through the higher number of offspring produced during a fixed time interval by a pair of parents from the adapted lineages on the stressful medium compared to the control (unadapted) lineage, and in the less pronounced delay in larval development caused by high NaCl concentration. The adaptation to stressful medium did not entail fitness costs on the standard (favorable) medium; moreover, it resulted in more effective reproduction in favorable conditions (expansion of the trophic niche). These results, together with those obtained earlier during the study of adaptation of D. melanogaster to nutrient-poor starch based medium, imply that adaptation to marginal conditions accompanied by positive (rather than negative) side effects, leading to the expansion of the trophic niche, may be a frequent phenomenon in eurytopic species like D. melanogaster, probably explaining, to some extent, their ecological tolerance. Scarcity of experimentally confirmed examples of such evolutionary scenario is probably due to low number of attempts to find them. One possible mechanism of 'multi-purpose adaptations' obtained during the acclimation to environmental stress is the adaptive changes of symbiotic microbiota which, in Drosophila, is efficiently transferred between generations if offspring eat the medium on which their parents had lived. For instance, high quantities of symbiotic lactobacilli in the gut can enhance larval growth, life span of adults, and the efficiency of substrate utilization. Further studies are needed to reveal the mechanisms responsible for the changes in fitness observed in the course of the experiment.