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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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FULL STORY
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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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