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A CORRELATION BETWEEN INITIATION OF DNA SYNTHESIS AND CELL DIVISION IN MYXOCOCCUS XANTHUS
No full textChromosome completion is a necessary condition for cell division in
Myxococcus xanthus as in many other bacteria. By taking advantage of the
unioue life cycle of M. xanthus we have been able to obtain evidence that
an additional and earlier linkage exists between DNA replication and
cell division in M. xanthus FBmpT.
In the presence of nalidixic acid (NAL) glycerol induced myxospores germinate
but do not divide (snake formation). In contrast , vegetative
cells treated with chloramphenicol (CAP) undergo one subsequent cycle of
division in the presence of NAL. This difference is surprising because
during both treatments (alycerol and CAP) similar kinetics of cell division
and DNA synthesis were obtained (immediate cessation of cell division;
about 40 % increase in DNA content). One possible explanation for
the failure of germinating myxospores to divide in the presence of NAL
is that durina myxospore formation chromosomes are blocked just prior
to completion. If this were the case, then cells in which chromosomes
were allowed to complete in the presence of CAP and subsequently induced
to form myxospores should divide in the presence of NAL. However, such
germinating myxospores with completed chromosome do not divide in the
presence of NAL.
Kinetics of DNA synthesis during myxospores formation following release
from amino-acid starvation showed that glycerol induction involves an
immediate cessation of new cycles of DNA replication. During germination
DNA synthesis started synchronous ly between 3 - 5 hrs, whereas the first
round of synchronous cell division appeared between 4 - 6 hrs indicating
that the first division follows a short interval of DNA synthesis. Treatment
of germinating myxospores with NAL at different time intervals indicated
that the critical time period in which DNA synthesis is necessary
for the first division beqan at 3.5 hrs. This time period (3.5-5 hrs) was
shown to involve only new initiations of DNA replication by the following
experiment: Myxospores induced by glycerol in the presence of NAL completed
their chromosomes during the first 4 hr of germination. Hence,
the potential for DNA elongation is present much earlier than the critical
time period mentioned above. It is proposed that the first division
following germination depends on DNA initiation. This requirement
is not the synthesis of DNA per se,but involves the synthesis of specific
RNA and protein triggered by DNA initiation: when germinating myxospores
were released from inhibition of DNA synthesis by removal of NAL
at 6 hrs, they failed to divide in the presence of CAP or rifampicin.
These data support the hypothesis that during normal growth a component
necessary for cell division is synthesized during initiation of DNA replication.
This hypothetical component is necessary for subsequent cell
division. During myxospore formation this component is destroyed
PROTEINVERWERTUNG VON SCP IN ABHANGIGKEIT VON UNTERSCHIEDLICHER FERMENTATION UND AUFBEREITUNG
No full textDie Zusammensetzung mikrobieller Biomasse und deren Verwertung durch das Tier wird
erst einmal durch den Mikroorganismus selbst bestimmt. Zu beeinflussen ist dies aber
auch durch den Fermentationsprozeß und insbesondere durch Maßnahmen der postfermentativen
Aufbereitung (1, 2, 3, 4, 5, 8, 9, 10, 11, 12). Zu den beiden letzteren Bereichen
werden einige Versuchsergebnisse zur Diskussion gestellt.
)
In Zusammenarbeit mit der GBF, Braunschweig-Stöckheim” wurde die Wirkung einer unterschiedlichen
Gestaltung des Fermentationsprozesses auf die Zusammensetzung, insbesondere
des Proteins und dessen Verwertung durch das Tier untersucht. Von den verschiedenen
Möglichkeiten der Prozeßführung wurden zwei Parameter, nämlich die
"Durchflußrate" und die "Substratversorgung" variiert. In der Tabelle 1 sind hierzu
einige Angaben gemacht
DEVELOPMENT AND APPLICATIONS OF AMPEROMETRIC BIOSENSORS
No full textRecent studies have led to the development of practical methods for making intimate
connections between the redox centres of oxidoreductases and conductors, for
example, the use of mediators such as ferrocenes or tetrathiafulvalenes. Based
upon these advances, second generation enzyme sensors of simple, cheap construction
able to operate on crude, untreated samples have been developed. For example, a
small pen-type pocket glucose sensor has been developed for the market by
Genetics International. The device shows considerable advantages over competing
technologies, especially with respect to user-friendliness. Developments of such
technology for non-medical applications, especially meat freshness monitoring and
in situ monitoring of substrate levels in fermenters and bioreactors is described.
Using related methods of electrochemical mediation, we have recently developed an
advanced prototype biosensor for rapid assessment of microbial contamination of
materials, including foodstuffs and industrial lubricants. This device which is
simple and cheap to manufacture, allows measurement of microbial activity within
two minutes. A major goal is exploitation of immunospecificity and DNA hybridisation.
We have demonstrated substantially improved performance of commercial enzyme
amplified ELISA methodology by replacing the end colour reaction by mediated
amperometric systems. Methods for the electrochemical detection and measurement
of antibodies labelled with non redox enzymes, especially alkaline phosphatase are
also available. For example, appropriate phosphorylated derivatives of ferrocene
are substrates for this enzyme and therefore facilitate sensitive mediated
amperometric detection. Related amperometric DNA probes can be constructed by
coupling such electrochemical methodology with for example, the avidin-biotin approach
using peroxidase labelling. A new method for rapid determination of iron in
physiological fluids exploiting the chelating agent desferrioxamine B is described
MAMMALIAN CELL CULTURE PROCESS CONTROL: 5 SAMPLING AND SENSING
No full textTheglobal opinion ofpotential customers about the analytical methods using biosensoris scepticism.
The main reason explaining this behavioris a lake of credibility of these technics.
The first biosensor concept has been described during the 60's, the first equipment commercially
available appeared during the end of 70's.
Few of these equipment are widely diffused.
Whatdoes it mean?
If one looks in the literature more than 1000 paperscan be easily found describing different biosensors to
analyse a lot of substances.
In actual fact, few of these probes have been developed and all these brillant concepts are quite far from
the industrial reality. Most of these authors have described experiments forgetting the real nature of the
samplesand the operating conditionsof the assay either in the industry or in the medical laboratory.
The credibility of these analytical technics has to be demonstrated, we have to show how they can be
successfully applied notonly at the laboratory scale but also at the industrial level. We have to go where
the analytical problem is.
However, current industrial needs for real time analysis to control a process cannotbe satisfied by
existing methods of analysis and induce researchs in this field. Developments in biosensors can
potentially open a new industrial market because they are able to deliver a fast response on a crude
sample. In an other hand, developments in molecular biology have stimulated new opportunities in both
microbial and mammaliancell culture. The increasing developmentof these production methodsresults
in a greater need for control systemsto Operate these processesat their optimal point. In line analytical
techniques, able to deliver data in real time are needed by biotechnological companies and have
motivated the developmentof biosensor.
Thecontrolof a process involving mammalian cell culture is summarizein the figure 1. We have applied
biosensors use for the estimation of L-glutamine, glucose and L-lactate concentrations
THE SLOW GROWING GRAM NEGATIVE PIGMENTED WATER BACTERIA
No full textBacteria, producing yellow to orange pigmented colonies on the surface of natural
and artificial media, can be found in virtually every segment of the environment.
They can be isolated from the soil, from fresh and salt water, from rain and snow,
as well as from man, animals, birds, fish and plants. The majority of pigmented organisms
are slow growing and can best be seen on the surface of agar plates and membrane
filter pads, but usually only after extended incubation of 5-15 days at room
temperatures, Some species appear to be chlorine tolerant and can be readily isolated
from domestic water supply outlets such as taps, spigots and drinking fountain
heads. They also grow readily in static water holding units such as tanks, water
baths and special equipment, commonly noted in laboratories and hospitals. Although
most of the yellow pigmented bacterial colonies can be classified as harmless microorganisms,
occurring in most natural water supplies; infections can and do occur
among infants, debilitated patients, surgical patients and patients on immunosupressive
drug therapy, chiefly through careless handling of water supplies contaminated
with these organisms,
The use and abuse of our natural fresh water supplies is an ever increasing
worldwide problem. Not only are the lakes and streams polluted by chemicals, fertilizers,
and insecticides from surface waters, but the sewage disposal practices encourage
the survival and growth of many undesirable species of microbes. Bayliss
/2/ in 1930 foresaw the coming events when he stated, "It is easy to remove microorganisms
and avoid other particles by filtration, but it is not easy to reduce the
organic content of many waters to the point where it will not support microbial
growth." The truth of this statement was verified many times over a period of
twenty years of microbiological analyses of water samples in a hospital and research
facility.
The samples came from many sources such as dynamic and free flowing and static
or stored water supplies especially in dead end or little used pipe lines, water
baths, reservoirs, tank and storage units. Most samples at one time or another,
contained viable mold spores, yeast cells, acid fast bacilli, aerobic and anaerobic
spore formers, micrococci, streptococci and diptheroids in addition to many species
of pigmented and nonpigmented gram negative rods /14/—some of which still remain to
be classified as this symposium is attempting to demonstrate. Our attention was
first drawn to this problem when four open heart surgery patients developed a bacteremia
during their convalescent period /4/. Environmental studies demonstrated a
similar organism in a water bath for tempering blood in the surgical area, and in
the watér cooling system of the heart lung machine used on the four patients, as was
isolated from blood cultures of these patients. Subsequent environmental studies
showed that various species of pigmented gram negative bacteria could be readily
isolated from the water from virtually every area, in varying numbers, of the research
complex.
Since water is the "almost universal" solvent, it is able to extract both beneficial
and harmful components from the soil or surfaces over or through which it
flows and percolates that give it flavor, odor, color, hardness, acidity, alkalinity,
and the nutrients that support and encourage microbial growth before, during and
after routine use and handling. Chambers and Clarke /7/ describe it clearly, "the
extent to which water can serve as a bacterial growth medium is one of the least
recognized facets of microbiology."
The typical water bacteria, i.e., the pigmented gram-negative, non-fermenting,
slow growing species require somewhat different conditions for optimum development.
Pigment is most readily produced on the surface of agar plates incubated at room
temperature for 5-15 days. The slow growth is not limited to artificial media,
since samples of water held at room temperature show a slow but steady increase in
numbers, while the levels of coliforms or other non-pigmented species usually decrease
during similar holding periods
REPAIR-RESISTANT NUCLEOSIDE ANALOGUES IN OLIGONUCLEOTIDE-DIRECTED MUTAGENESIS
No full text2'-Deoxytubercidin (a) and 2'-deoxy-7-deazainosine (b) were used as
analogues of deoxyadenosine and deoxyinosine respectively for the introduction
of transition mutations into the a-peptide fragment of the
lacZ gene encoded in the filamentous bacteriophage Ml13mp9. Using conventional
methodology of oligonucleotide-directed mutagenesis, the
number of desired point mutants was very low (2-6%) for both T+C and
C+T transitions, due to the efficient removal of purine/pyrimidine
mismatches by the repair machinery of E. coli. Following the incorporation
(via synthetic oligodeoxyribonucleotides) of the purine nucleoside
analogues a and b into the mismatch sites, the yield of desired
mutants was increased approximately tenfold
ERFAHRUNGEN MIT DER BIOMASSERÜCKHALTUNG AN KONTINUIERLICHEN FERMENTATIONEN MITTELS FILTRATION
No full textDie Filtration zur Zellseparation bei einer Biomasseriickhaltung ist die Methode
der Wahl, wenn die Biomasse schlecht sedimentierbar oder flotierbar ist und eine
Immobilisierung nicht sinnvoll ist. An kontinuierlichen Kulturen des myzelbildenden
Cellulaseproduzenten Trichoderma reesei sowie einer definierten, methanogenen
Mischkultur zum anaeroben Abbau essigsäurehaltiger Abwässer wird gezeigt, daß
sich die Anwendbarkeit von Cross-Flow-Filtration und Rotorfilter dabei auch auf
scherkräftesensitive Organismen erstreckt
SOLID STATE SENSORS BASED ON CHEMICAL MODULATION OF ADMITTANCE OF BIOLOGICAL MEMBRANES
No full textBarrier properties of phospholipid membranes to small inorganic
ions can be modulated by addition of chemical species to the solution
which adsorb at the solution/membrane interface or which penetrate
into the membrane hydrophobic interior. With additional highly
selective receptors such membranes could serve as the basis for new
class of chemical sensors. This concept has been recognized [1] and
various attempts have been made to implement synthetic phospholipid
membranes in a sensor configuration
FIBRE-OPTIC SENSORS FOR CHEMICAL PARAMETERS OF INTEREST IN BIOTECHNOLOGY
No full textOptical fibres can be used for remotely sensing chemical and physico-chemical parameters
that are of interest for proper management of bio- processes as they occur, for
instance, in bioreactors. Optical sensors can offer advantages over electrochemical
ones because of the lack of reference cells, the immunity towards electromagnetic
interferences, and the possibility of heat sterilisation. In this contribution, the
principles of waveguide spectroscopy are briefly outlined, and waveguide sensors are
classified according to their working principles.
The most usual approach in the development of fibre-optic sensors is to provide the
end of an optical fibre with a suitable indicator chemistry or a material that
responds to the parameter of interest. In contact with the sample, the intensity of
reflected, scattered, or re-emitted light is the analytical signal.
Representative examples of fibre-optic sensors for oxygen, pH, carbon dioxide,
ammonia, electrolytes, and redox status are given. Recently developed sensors for
glucose and enzymes shall also be considered. Finally, potential fields of application
are presented, and current trends and concepts discussed
A DISPOSABLE OPTICAL BIOSENSOR BASED ON TOTAL INTERNAL REFLECTION FLUORESCENCE
No full textA novel disposable biosensor device is described, based on the generation
of evanescent light waves at an optical interface. The sensor is
injection moulded from high optical quality plastic and consists of
two parts, the waveguide and a cuvette for containing the sample solution.
Antigens are attached to the waveguide surface and the reaction
with antibodies is monitored by exciting and collecting fluorescent
light "back-tunneled" out of the waveguide. A model assay for human
IgG is used to demonstrate that this biosensor can give rapid, sensitive
results