How a gooey slime helps bacteria survive

Date:
August 3, 2020
Source:
University of Tsukuba
Summary:
Researchers found that the bacterium C. perfringens modulates the
structure of its biofilm at different temperatures by regulating
the expression of the novel extracellular protein BsaA. They
showed the number of BsaA-producing cells decreases when the
temperature increases from 25DEGC to 37DEGC, and BsaA-producing
cells cover non-BsaA-producing cells to provide tolerance to
external stresses. These findings help us understand how bacteria
adapt to their environment to survive.



FULL STORY ========================================================================== Bacteria have the ability to adapt to their environment to survive the
host's immune defense. One such survival strategy includes the formation
of a biofilm that prevents the immune system or antibiotics from reaching
the bacteria. In a new study, researchers from the University of Tsukuba revealed that modulations to biofilm structure as a result of temperature changes are regulated by the production of a novel extracellular protein
called BsaA in the bacterium C.

perfringens produces.


==========================================================================
C. perfringens lives in various environments, soil and the
intestines of animals, and can cause food poisoning, gas gangrene and antibiotics-associated diarrhea. It is anaerobic bacterium that is not
able to grow outside a host due to the presence of oxygen. While it is
common knowledge that it can turn into spores to evade environmental
attacks, it was not until recently that C.

perfringens was shown to also have the ability to form biofilms. In
these biofilms, a community of C. perfringens bacteria cover themselves
in a dense matrix of so-called extracellular polymeric substances (EPS)
-- which contain proteins, nucleic acids, and sugar molecules -- thus protecting themselves from external hazards. To date, it has remained
unclear how C. perfringens is using biofilms to survive in oxygen-rich environments.

"We have previously shown that temperature is an environmental cue that influences C. perfringens biofilm morphology," says corresponding author
of the study Professor Nobuhiko Nomura. "Although at higher temperatures,
such as 37DEGC, the bacteria attach to surfaces and pack densely
in an adherent biofilm, at lower temperatures they build a thicker, pellicle-like biofilm. We wanted to know how they are able to modulate
the structure of their biofilm in response to temperature changes."
To achieve their goal, the researchers constructed a library of 1,360
mutant (gene knockout) cells in C. perfringens to see which proteins
are required to form a pellicle-like biofilm at 25DEGC. Throughout their screening, they noticed the presence of a new protein called BsaA that
is produced inside the bacteria and transported to the exterior. Without
BsaA, the bacteria formed either a fragile pellicle biofilm or an adherent biofilm only. The researchers then showed that multiple BsaA proteins
assemble at a polymer outside the cells to enable the formation of a
stable biofilm. When exposed to the antibiotic penicillin G or oxygen,
C. perfringens lacking BsaA had a significantly decreased survival rate compared with normal C. perfringens.

"Our results show that BsaA is necessary for pellicle-like biofilm
formation at 25DEGC and conferral of tolerance to antibiotics," says
lead author of the study Professor Nozomu Obana. "We know that biofilms
contain heterogeneous cell populations, which leads to multicellular
behaviors. We therefore wanted to know whether cellular heterogeneity
affects the production of BsaA and thus the formation of a pellicle-like biofilm." The researchers found that the protein SipW controls the polymerization of BsaA to a biofilm, and used this to study biofilm
formation. By constructing C.

perfringens that produced a fluorescent protein when SipW is produced,
thus allowing these cells to be tracked by fluorescent microscopy,
the researchers were able to show that not all bacteria produced
SipW. Additionally, they found that the population of SipW-producing
bacteria started to drop significantly when the temperature was increased
from 25DEGC to 37DEGC. Intriguingly, at 25DEGC, cells that did not
produce SipW were located next to the surface the bacteria were sitting
on, and were covered by SipW-producing cells.

Heterogeneous production of SipW, and thus BsaA, might therefore ensure
that those cells that have a higher tolerance to external hazards protect
the bacterial subpopulation at risk.

"At 25DEGC, C. perfringens are more likely to be exposed to external
stresses.

Our results provide an explanation for how a community of C. perfringens ensures that it stays protected when the temperature changes. Our study
aids understanding of biofilm properties and provides insights into the development of new antibacterial strategies," says Professor Nomura.


========================================================================== Story Source: Materials provided by University_of_Tsukuba. Note: Content
may be edited for style and length.


========================================================================== Journal Reference:
1. Nozomu Obana, Kouji Nakamura, Nobuhiko Nomura. Temperature-regulated
heterogeneous extracellular matrix gene expression defines biofilm
morphology in Clostridium perfringens. npj Biofilms and Microbiomes,
2020; 6 (1) DOI: 10.1038/s41522-020-00139-7 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/08/200803105237.htm

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