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    STUDIA BIOLOGIA - Issue no. 1 / 2019  
         
  Article:   EXTREMOPHILES EVERYWHERE AND THE LIMITS OF MICROBIAL LIFE.

Authors:  EMESE BARTHA, TERRY J. MCGENITY, BOYD A. MCKEW, ETIENNE LOW-DECARIE.
 
       
         
  Abstract:  Microorganisms capable of growing in extreme conditions were expected to be only found living in extreme environments. However, recent studies found extreme-tolerant microbes (extremotolerants) in non-extreme environments. What is the environmental limit of extremotolerants? Will they have a lower growth rate than endemic microbes in non-extreme environments? Here we sampled microbial communities from three rivers and their connected marine sites and enriched for extremophiles/extremotolerants in seven different media: yeast extract plus various high concentrations of ZnCl2, CuSO4 (metalotolerants), NaCl (halophiles/ halotolerants), MgCl2 (chaophiles/ chaotolerants), sorbitol (osmophiles/ osmotolerants), HCl, and NaOH (acidophiles/ acidotolerants and alkaliphiles/ alkalitolerants, respectively). Samples were enriched in these seven stressor media separately, along with control samples enriched in yeast extract media. These communities enriched in stressor and control media were inoculated in a gradient of the same type of stressor. We found that stressor-enriched cultures had a higher tolerance to stress conditions and could grow at a wide range of stressor concentrations compared to control-enriched cultures that only grew at low stressor levels. These differences were especially apparent for NaCl and MgCl2. Therefore, these stressor-enriched communities could potentially consist of previously dormant obligate extremophiles and/or facultative extremotolerants surviving/growing in non-extreme conditions. These findings further support the theory that microorganisms can be found far outside of their physiologically optimal habitat, and question whether extremotolerants living in non-extreme environments differ from their counterparts in extreme environments.

Keywords: chaophile, extremophile, extremotolerant, halophile, microbial biogeography.
 
         
     
         
         
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