Bacteria employ a diverse array of strategies to survive under extreme environmental conditions but maintaining these adaptations comes at an energetic cost. If energy reserves drop too low, extremophiles may enter a dormant state to persist. We estimated bacterial dormancy and identified the environmental variables influencing our activity proxy in 10 hypersaline and freshwater lakes across the Western United States. Using ribosomal RNA:DNA ratios as an indicator for bacterial activity, we found that the proportion of the community exhibiting dormancy was 16% lower in hypersaline than freshwater lakes. Based on our indicator variable multiple regression results, saltier conditions in both freshwater and hypersaline lakes increased activity, suggesting that salinity was a robust environmental filter structuring bacterial activity in lake ecosystems. To a lesser degree, higher total phosphorus concentrations reduced dormancy in all lakes. Thus, even under extreme conditions, the competition for resources exerted pressure on activity. Within the compositionally distinct and less diverse hypersaline communities, abundant taxa were disproportionately active and localized in families Microbacteriaceae (Actinobacteria), Nitriliruptoraceae (Actinobacteria), and Rhodobacteraceae (Alphaproteobacteria). Our results are consistent with the view that hypersaline communities are able to capitalize on a seemingly more extreme, yet highly selective, set of conditions and finds that extremophiles may need dormancy less often to thrive and survive.
Extremophiles employ a diverse array of resistance strategies to thrive under harsh environmental conditions but maintaining these adaptations comes at an energetic cost. If energy reserves to drop too low, extremophiles may enter a dormant state of reduced metabolic activity to survive. Dormancy is frequently offered as a plausible explanation for the persistence of bacteria under suboptimal environmental conditions with the prevalence of this mechanism only expected to rise as stressful conditions intensify. We estimated dormancy in ten hypersaline and freshwater lakes across the Western United States. To our surprise, we found that extreme environmental conditions did not induce higher levels of bacterial dormancy. Based on our approach using rRNA:rDNA gene ratios to estimate activity, halophilic and halotolerant bacteria were classified as inactive at a similar percentage as freshwater bacteria, and the proportion of the community exhibiting dormancy was considerably lower (16%) in hypersaline than freshwater lakes across a range of cutoffs estimating activity. Of the multiple chemical characteristics we evaluated, salinity and, to a lesser extent, total phosphorus concentrations influenced activity. But instead of dormancy being more common as stressful conditions intensified, the percentage of the community residing in an inactive state decreased with increasing salinity in freshwater and hypersaline lakes, suggesting that salinity acts as a strong environmental filter selecting for bacteria that persist and thrive under saltier conditions. Within the compositionally distinct and less diverse hypersaline communities, abundant taxa were disproportionately active and localized in families Microbacteriaceae (Actinobacteria), Nitriliruptoraceae (Actinobacteria), and Rhodobacteraceae (Alphaproteobacteria). Our results demonstrate that extreme environments may not necessarily be stressful or suboptimal for highly adapted extremophiles causing them to need dormancy less often to survive.
Extremophiles employ a diverse array of resistance strategies to thrive under harsh environmental conditions but maintaining these adaptations comes at an energetic cost. If energy reserves to drop too low, extremophiles may enter a dormant state of reduced metabolic activity to survive. Dormancy is frequently offered as a plausible explanation for the persistence of bacteria under suboptimal environmental conditions with the prevalence of this mechanism only expected to rise as stressful conditions intensify. We estimated dormancy in ten hypersaline and freshwater lakes across the Western United States. To our surprise, we found that extreme environmental conditions did not induce higher levels of bacterial dormancy. Based on our approach using rRNA:rDNA gene ratios to estimate activity, halophilic and halotolerant bacteria were classified as inactive at a similar percentage as freshwater bacteria, and the proportion of the community exhibiting dormancy was considerably lower (16%) in hypersaline than freshwater lakes across a range of cutoffs estimating activity. Of the multiple chemical characteristics we evaluated, salinity and, to a lesser extent, total phosphorus concentrations influenced activity. But instead of dormancy being more common as stressful conditions intensified, the percentage of the community residing in an inactive state decreased with increasing salinity in freshwater and hypersaline lakes, suggesting that salinity acts as a strong environmental filter selecting for bacteria that persist and thrive under saltier conditions. Within the compositionally distinct and less diverse hypersaline communities, abundant taxa were disproportionately active and localized in families Microbacteriaceae (Actinobacteria), Nitriliruptoraceae (Actinobacteria), and Rhodobacteraceae (Alphaproteobacteria). Our results demonstrate that extreme environments may not necessarily be stressful or suboptimal for highly adapted extremophiles causing them to need dormancy less often to survive.
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