Supplement bij veertiende jaargang, april 2006 - NVMM

06.08
Fungal spores as survival capsules in time and space
J. Dijksterhuis
Applied and Industrial Mycology, Centraalbureau voor
Schimmelcultures, Utrecht
The variety of fungal spores is bewildering, but there main
function is distribution. They can serve for propagation
of the fungus from adverse locations towards better
conditions. These spores often are produced in large
numbers and are transported through air, water or by
the action of living organisms. Spores also can serve for
dispersion in ‘time’ by literally waiting for better times.
These spores often have thick cell walls and are not
dispersed. These spores show constitutive dormancy,
that is a metabolic block that is released only after special
triggers. Further, these spores can be highly resistant
to many stressors and exhibit different very specialised
features during dormancy and germination as in case
of the fungus Talaromyces macrosporus. Communication
between spores or spore compartments (in case of multicellular
spores) may serve a fine-tuning of the rather
stochastic process of distribution. Examples of such
processes are discussed with the fungi Penicillium paneum
and Fusarium culmorum. The apparatus of spore dispersal
is highly specialised and may be prone to quick devaluation
when not extensively used, as is discussed with the fungus
Rhizopus oligosporus.
06.09
global regulation of survival strategies of the bacterial spore
former Bacillus cereus
T. Abee 1,2 , M. Tempelaars 1,2 , M. van der Voort 1,2 ,
J. Wijman1,2 , W. van Schaik1,2 , M. Zwietering 1 , W. de Vos2 1
Laboratory of Food Microbiology, Wageningen University,
Wageningen, 2Wageningen Centre for Food Sciences,
Wageningen
Bacillus cereus is a common cause of food-borne disease
that thrives in many different ecological niches. For the
control of this pathogen, it is especially relevant to know
which mechanisms it can utilize to sustain growth in
the many environments that it can inhabit. We aimed to
assess global regulation in B. cereus highlighting the role
of a range of sigma factors, including the general stress
sigma factor s B , the early sporulation sigma factor s H , and
a number of selected extra-cytoplasmic-function (ECF)
sigma factors, and the catabolite control protein CcpA in
the performance of B. cereus under various growth and
stress conditions, relevant in the processing and preservation
of foods.
Using B. cereus ATCC 14579 and targeted sigma factor- and
ccpA-deletion mutants, the impact of these regulators and
Ned Tijdschr Med Microbiol 2006; 4:Supplement
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their regulons on B. cereus growth performance, stress
response, sporulation efficiency and surface behaviour,
including swarming and biofilm formation, were assessed.
In addition, proteomics and gene profiling, employing
B. cereus whole genome ORF-based micro-arrays, are
used to further identify key elements in B. cereus ecophysiology
and virulence that may affect its performance
and survival in industrial settings. This approach showed
an involvement of s B in stress response, roles for s H and
an ECF sigma factor in sporulation and biofilm formation,
and regulatory roles of CcpA in key metabolic pathways,
biofilm formation, and sporulation.
06.10
Mode-of-action of high pressure low temperature induced
damage to Bacillus subtilis in the IceI-IceII domain
T. Shen1,2 , A. Bos 2 , S. Brul 1,2
1
Swammerdam Institute for Life Science, Faculteit der
Natuurwetenschappen, Wiskunde en Informatica, Amsterdam,
2Unilever Food & Health Research Institute, Advanced Food
Microbiology, Vlaardingen
The damages on Bacillus subtilis vegetative cells induced
by subzero temperatures and pressures up to 250MPa
in buffer solution (i.e. in the area of IceI-IceIII phase
transitions) was studied by means of flowcytometry in
combination with membrane permeability and viability
probes: PI (propidium iodide) and cFDA (carboxyfluorescein
diacetate). The growth of single cells was traced
by measuring the optical density and light scatter of the
growth medium. Bacterial cells showed high heterogeneity
in stress resistance to the treatment. Treated cells displayed
a distribution into four populations characteristically
by green (cFDA) and red (PI) fluorescent intensity: high
green/low red; high green/high red; low green/high red;
and low green/low red. Single cells from C in TSB (trypcase
soy broth). Each population were sorted and incubated at 25
Very few cells from the high red populations were found
to grow after 50 days. A number of wells gated from the
low red populations showed positive growth after 2.5-20
days, while the lag time of untreated cells was only around
0.7 day under the same growth condition. The lag time of
the cells treated with different conditions does not differ
significantly. Untreated cells sporulate immediately after
reaching the maximum growth, which is less than 2 days’
incubation. Finally, on the one hand, most cells treated
by either freezing or HPLT generally show slower growth
rate. These cells did not sporulate even 25 days after the
onset of growth. On the other hand, cells sorted both from
populations of high green/low red and low green/low red
resulted in a similar number of positive wells and lag time.
Conclusions: 1) Plasma membrane damage seemed to
be the first mode-of-action of HPLT on the bacteria. 2)