MSGID: 1:317/3 646c4163   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    What you count is not necessarily what counts    
    A new study focusing on the number of dividing bacterial cells in the   
   North Sea challenges some dogmas about marine microbial life.    
      
     Date:   
         May 22, 2023   
     Source:   
         Max Planck Institute for Marine Microbiology   
     Summary:   
         Seawater is full of bacteria, hundreds of thousands live in   
         every liter.   
      
         But the sheer number of bacteria living in the water does not   
         necessarily mean a lot. More important is how active they are and   
         how quickly they duplicate.   
      
      
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   If scientists want to find out how fast a population of bacteria grows,   
   they often measure how their cell count changes over time. However,   
   this method has a major flaw: it does not measure how fast the bacteria   
   multiply or die. Yet these factors are very important for understanding   
   ecological processes. That is why researchers at the Max Planck Institute   
   for Marine Microbiology in Bremen have now taken a closer look at these   
   processes during a spring bloom in the German Bight. In doing so, they   
   challenge some previous dogmas.   
      
   The researchers around Jan Bru"wer, Bernhard Fuchs and Rudolf Amann   
   investigated the growth of bacteria during the spring bloom off Helgoland   
   using various methods: With the microscope, they counted and identified   
   not only the cells present, but also the frequency of cells that were   
   currently dividing.   
      
   This way, they were able to calculate how quickly different types of   
   bacteria multiplied in their natural environment.   
      
   "We used modern microscopic methods to visualise and count dividing cells   
   in thousands of images," explains Jan Bru"wer, who conducted the study   
   as part of his doctoral thesis. "We made use of the fact that a dividing   
   cell has to split its duplicated genome into its daughter cells. Thus,   
   we were able to clearly identify these cells based on the DNA distribution   
   in the cell." This enabled the researchers to determine the growth rates   
   of individual groups of bacteria over longer periods of time.   
      
   "The results had some surprises in store for us," says group leader   
   Bernhard Fuchs. "For example, we found that the most common group of   
   bacteria in the ocean, called SAR11, divides almost ten times faster than   
   assumed." Moreover, in many cases the measured growth rates do not match   
   the abundance of the respective bacteria in the water. "If bacteria divide   
   often but are not abundant, it suggests that they are a popular victim   
   of predators or viruses," Bru"wer explains. "The timing of bacterial   
   proliferation was also surprising: SAR11 bacteria frequently divided   
   before the onset of the algal bloom in the North Sea. From where they   
   took the required energy to do so is still a mystery."  Not all bacterial   
   groups behaved as unexpectedly as SAR11; for other groups, the results   
   now collected were more in line with the researchers' expectations --   
   in their case, growth rates and cell numbers largely matched.   
      
   Until now, it has been assumed that SAR11, which have very small cells,   
   get by with little nutrients, do not divide very often and are eaten only   
   rarely because of their small size. In contrast, other larger bacteria,   
   for example the Bacteroidetes, are seen as popular food, multiplying   
   quickly and disappearing just as quickly when predators and viruses get   
   on their trail. The new study by Bru"wer and his colleagues paints a   
   very different picture.   
      
   "Our results influence our understanding of element cycles, especially   
   the carbon cycle, in the ocean," Bru"wer emphasises. "The most abundant   
   bacteria in the ocean, SAR11, are more active and divide faster than   
   previously believed.   
      
   This could mean that they need fewer nutrients and are a more popular food   
   source for other organisms than suspected. Also, the general turnover   
   of bacteria during algal blooms seems to be faster than we thought."   
   "This research was methodologically very demanding and it shows how much   
   information you can draw from microscopy images," stresses Rudolf Amann,   
   director at the Max Planck Institute for Marine Microbiology. "I am very   
   proud of the researchers involved for mastering this mammoth task and   
   glad to have the privilege to work with them. The results achieved will   
   trigger many exciting discussions about the ecological relationships   
   during a spring bloom and in the ocean in general."   
       * RELATED_TOPICS   
             o Plants_&_Animals   
                   # Bacteria # Microbiology # Microbes_and_More #   
                   Extreme_Survival   
             o Earth_&_Climate   
                   # Ecology # Geochemistry # Oceanography # Geography   
       * RELATED_TERMS   
             o Bacteria o Algal_bloom o Microorganism o Honey o Herbivore   
             o Sea_water o Body_odor o Virus   
      
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   Story Source: Materials provided by   
   Max_Planck_Institute_for_Marine_Microbiology. Note: Content may be edited   
   for style and length.   
      
      
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   Journal Reference:   
      1. Jan D. Bru"wer et al. In situ cell division and mortality rates   
      of SAR11,   
         SAR86, Bacteroidetes, and Aurantivirga during phytoplankton blooms   
         reveal differences in population controls. mSystems, 2023 DOI:   
         10.1128/ msystems.01287-22   
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   Link to news story:   
   https://www.sciencedaily.com/releases/2023/05/230522131355.htm   
      
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