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Biofilm Paper

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Microbiology
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Influence of static and shaken environment in cell density and diversity of Pseudomonas
fluorescens SBW25 morphotypes
[name]
Introduction
Pseudomonas fluorescens is a γ proteobacterium that is widely distributed in soils and is
mostly isolated from the roots and leaves of plants. Strains of P. fluorescens are physiologically
and environmentally diverse. The heterogeneity among P. fluorescens strains has driven
researchers to suggest that strains of P. fluorescens develop a complex of species. One of its strains,
the SBW25, was isolated from the leaf surface of sugar beet at University Farm in Oxford, UK
and is known to be valuable in plant’s wellbeing and nutrition. The strain is also known to form
biofilm and secrete a greenish pigment, especially under states of low iron accessibility. Although
the strain is beneficial to plants, it is a major threat to immunocompromised individuals (Scales et
al., 2014).
Due to its complexity, the strain SBW25 consists of three morphotypes, smooth type which
is the common one, and the wrinkly spreader and fuzzy spreader which are both adaptive
morphotypes. In the study of Rainey & Travisano (1998), they utilized the same strain to
investigate the role of ecological factors and competition in the genetic diversity and adaptive
evolution of the morphotypes. The authors found out that when ecological opportunity is present,
SBW25 colonies appear to be morphologically diverse but when such opportunity is prevented, no
variation was observed.
In this study, SBW25 strain is used to examine the changes in its morphological density
and diversity when external factors are added. This was done through shaking during incubation.

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It is expected that colonies in static environment will produce greater diversity due to having stable
environment.
Methods
Aliquoting media
Microcosm vials containing the strains were prepared. Each vial represents the following:
vial 1 consists of bacteria in a static environment and vial 2 represents bacteria in shaken
environment. 16 test tubes containing 4.5 mL of King’s B (KB) liquid media were prepared and
labelled to represent 8 dilutions in each microcosm environment.
Homogenization, serial dilution, and dilution plating
The microcosm contents in vials were first vortexed to release solids and clumps from their
attachment to the glass. Then, 500 µL of the microcosm content from the vial was transferred in
each test tube labelled with 10
-1
dilution and another 500 µL from the first dilution was then
transferred to the 10
-2
test tubes until the eighth dilution to complete the serial dilution step.
Before plating, each KB agar plate was suspended with 5-10 glass beads. Afterwards, 50
µL of the microcosm contents from 10
-5
, 10
-6
, 10
-7
, and 10
-8
dilutions were transferred into the
center of appropriate labelled KB petri plates in duplicate, gently shaken, and waited to be
absorbed and dried. Then, the glass beads were carefully removed before incubating the inverted
plates at 28
o
C for 48 hours. Morphology of colonies as well as their density and diversity different
microcosm were observed, listed, and calculated afterwards.

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Influence of static and shaken environment in cell density and diversity of Pseudomonas fluorescens SBW25 morphotypes [name] Introduction Pseudomonas fluorescens is a γ – proteobacterium that is widely distributed in soils and is mostly isolated from the roots and leaves of plants. Strains of P. fluorescens are physiologically and environmentally diverse. The heterogeneity among P. fluorescens strains has driven researchers to suggest that strains of P. fluorescens develop a complex of species. One of its strains, the SBW25, was isolated from the leaf surface of sugar beet at University Farm in Oxford, UK and is known to be valuable in plant’s wellbeing and nutrition. The strain is also known to form biofilm and secrete a greenish pigment, especially under states of low iron accessibility. Although the strain is beneficial to plants, it is a major threat to immunocompromised individuals (Scales et al., 2014). Due to its complexity, the strain SBW25 consists of three morphotypes, smooth type which is the common one, and the wrinkly spreader and fuzzy spreader which are both adaptive morphotypes. In the study of Rainey & Travisano (1998), they utilized the same strain to investigate the role of ecological factors and competition in the genetic diversity and adaptive evolution of the morphotypes. The authors found out that when ecological opportunity is present, SBW25 colonies appear to be morphologically diverse but when such opportunity is prevented, no variation was obse ...
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