VOLUM OMAGIAL - Facultatea de Ştiinţe ale Naturii şi Ştiinţe Agricole

Aurelia Manuela Moldoveanu, Ioan Ardelean / Ovidius University Annals, Biology-Ecology Series 14: 147-156 (2010)
temperature variation (16º C, 23º C, 29º C) and
registers a decrease of the quantity of inoculate from
1.2 ∙10 8 cel/l to 1.2∙10 2 cel/l used with the increase of
temperature, as well as an increased adhesion at high
temperatures during the first hours from immersion.
Experiments were realizes by Else [5] regarding
the bacterial colonization of the hydrophile surface of
metals (stainless steel, titanium and nickel) in
variable conditions of temperature (30º C, 60º C and
70º C) and humidity over a longer period of time
(from a few days to 18 months). They observed an
increase of adherent bacteria between 1.06∙10 2 cel/cm
2 and 7.61 ∙10 2 cel/cm 2 at a temperature of 30º C on
steel plates. They also observed a decrease of the
number of bacteria from the first day for the plates
exposed to high temperatures (60º C and 70º C),
especially on those of nickel and steel.
In what regards the role of the bacterial film in
the mediation of invertebrate attachment and fouling
formation, Lau et al. [35] realized experiments at
different temperatures (16º C, 23º C and 30º C),
noticing an increase in the number of bacteria from
14.3∙10 3 cel/mm -2 at 16º C to 21.2∙10 3 cel/mm -2 at
30º C. The experiments emphasized a more
significant influence of the temperature on the
biomass than on the bacterial density.
A number of experiments regarding the
formation of biofilms in different conditions of
temperature were realized by Di Bonaventura [36]
together with other collaborators accomplish in 2007
(4º C, 12º C, 22º C, 37º C) by Listeria
monocytogenes on the hydrophile surface of glass,
steel and the hydrophobe surface of polystyrene. The
results emphasized a progressive increase on the
surface at 4 ºC of 0.206, at 12 ºC BPI to 0.233 BPI,
22º C to 0.366 BPI, in comparison to polystyrene and
stainless steel. At 37º C the values are close to those
from the three surfaces studied, but there is also
greater species variability. Still, the most
considerable growth of 1.275 was obtained on the
hydrophobe surface of polystyrene.
Bacterial density registers an increase of the
adherent bacteria with higher values for the biofilm
formed in aquarium water kept at 18 ºC, compared to
the one kept at 6 ºC. The values obtained are higher
than those for seawater, which is due to the different
physical and chemical properties of aquarium water
and to the nutrients. Adherent marine bacteria attach
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themselves to surfaces and form microcolonies in the
first hour after immersion in the marine medium.
They grow in size with the immersion period, data
confirmed by [24].
3.3 The formation of biofilms under the
influence of salinity
Variation of salinity was done in order to
observe the influence of osmotic conditions on the
process of bacterial adherence and the formation of
the initial phases of biofilms. For the slides immersed
in containers with seawater with 15g/l salinity, Figure
3 displays an increase of bacterial density to 12∙10 2
cel/mm 2 one hour after immersion towards a
doubling of this value to 25∙10 2 cel/mm 2 eight hours
later.
The slides were left over night for 12 hours and
the following day there was a progressive increase of
the cellular density value of 49∙10 2 cel/mm 2 where
there is a tendency for a triple value towards 62∙10 2
cel/mm 2 .
In the case of containers with seawater with
modified salinity (addition of osmosis water 10g/l),
the bacterial density increased to 4∙10 2 cel/mm 2 one
hour after immersion to a double value of 8∙10 2
cel/mm 2 after four hours and the progressive increase
from 18 ∙10 2 cel/mm 2 after eight hours when there is
a tendency to triple the value of bacterial density.
After the 12 hour interval when the slides were left
over night in containers, there is an increase of the
cellular density from 41∙10 2 cel/mm 2 24 hours after
immersion to 54∙10 2 cel/mm 2 36 hours after
immersion. The growth progression during the first
12 hours in the case of the biofilms formed at a
salinity of 15g/l is higher, with a value of 2.3 and
displays a decrease after 24 hours to 1.1. In the case
of the biofilms formed at a salinity of 10g/l, the
growth progression is 2.4 during the first 12 hours
and it decreases after 24 hours to 1.1. The difference
between the two progressions is 2∙10 2 cel/mm 2 in the
first 12 hours, it increases to 8∙10 2 cel/mm 2 24 hours
after immersion and remains constant at this value
until 36 hours.
In the case of containers with seawater with
modified salinity (addition of osmosis water 5g/l),
Figure 4 displays an increase of bacterial density
from 2∙10 2 cel/mm 2 one hour after immersion to a