File Name: relation between cell division rate and growth rate of bacteria 2000 to 2018.zip
The kinetic model of cell growth is substantially capable to predict product formation. Mathematical models provide a strategy for solving problems encountered in fermentation process.
- Sources, propagation and consequences of stochasticity in cellular growth
- Pogil activities for ap biology protein structure
- Bacterial growth, detachment and cell size control on polyethylene terephthalate surfaces
Proteins are of great nutritional value and are directly involved in the chemical processes essential Their importance was recognized in the early 19th century. All organisms use the same fundamental mechanism for gene expression.
Sources, propagation and consequences of stochasticity in cellular growth
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However, the detailed quantitative information about the dynamics and the mechanisms involved in bacterial proliferation on solid substrates is still lacking. In this study we investigated the adhesion and detachment, the individual growth and colonisation and the cell size control of Escherichia coli E.
The results show that the bacterial growth curve on PET exhibits the distinct lag and log phases, but the generation time is more than twice longer than in bulk medium. Single cells in the lag phase are more likely to detach than clustered ones in the log phase; clustered bacteria in micro-colonies have stronger adhesive bonds with surfaces and their neighbours with the progressing colonisation.
We show that the cell size is under the density-dependent pathway control: when the adherent cells are at low density, the culture medium is responsible for coordinating cell division and cell size; when the clustered cells are at high population density, we demonstrate that the effect of quorum sensing causes the cell size decrease as the cell density on surfaces increases. A significant proportion of food-industrial equipment and medical devices become the focus of biofilm infections, causing lethal illnesses and heavy costs in maintenance 1 , 2.
Hence, biofilm has been of considerable interest in medical and food industry, as well as in academic research 1 , 3. Biofilms are complex communities of bacteria that develop on solid surfaces and enclose themselves in an extracellular polymeric substance EPS matrix 4 , 5 , which acts to protect bacteria from antibiotics, disinfectants and environmental insults 6 , 7 , 8.
The formation of biofilm mainly proceeds in three steps: 1 the initial adhesion of bacterial cells to surfaces, which has been widely studied 9 , 10 , This step is strongly influenced by the topographical and chemical features of the surface. Bacterial extracellular appendages such as flagella and fimbriae also play an important role in the attachment process 10 , The next stage is: 2 proliferation of the adherent bacteria and synthesis of the EPS matrix 6 , 13 , followed by the final step: 3 biofilm maturation followed by detachment and lysis of part of biofilms, thus releasing free bacteria to begin another biofilm growth cycle 10 , Over the last decade, much progress has been achieved in studying the steps 2 and 3.
For instance, biochemical and genetic methods were used to study the production of EPS and biofilm-generating systems 8 ; the microscopic methods have helped to determine the overall morphology and detachment of biofilms 1 , 14 , 15 , However, the studies of dynamics of bacterial proliferation after adhesion in the second step are still lacking and, in general, the bacterial colonisation on substrates is yet to be better understood. The conventional population growth in bulk liquid medium is a very well-studied subject In this study we are interested in what bacterial growth curve on solid surfaces would be like: whether distinct phases could also be observed and if so — what the growth rate and generation time would be?
When bacteria are introduced into the fresh medium in a closed system, like a test tube, the population of cells always exhibits growth dynamics as follows. Lag phase: bacteria initially adjust to the new environment, so they appear not able to replicate but the cells might grow in volume; Log exponential phase: cells start dividing regularly by the process of binary fission.
The culture reaches the maximum growth rate, which could be estimated by generation time or doubling time, i. Dead phase: bacteria lose the ability to divide and the number of dead cells exceeds that of live cells. Coordination between cell growth and division ensures an appropriate bacterial cell size for a given environmental condition and developmental fate Based on the dynamics of bacterial growth and division on surfaces with unlimited external nutrient supply, we also discuss the changes in the cell size as the population grows and attempt to construct a model for the control of cell size under such conditions.
The bacterial size control during periods of steady growth in the bulk culture medium has been extensively studied in the last decade 18 , It is established that FtsZ, the major cytoskeletal protein during binary fission, plays a vital role in the cell size control When the accumulation of FtsZ in the cell reaches a critical level, this protein self-assembles to form a contractile ring structure the FtsZ ring or Z-ring under the membrane at the future division site the centre of the cell , thereby triggering cell division.
It was determined that the regulation of the FtsZ assembly controls the timing of cell division, subsequently altering the cell size More recently, a nutrient-dependent metabolic pathway has been widely studied to describe the mechanism of cell size regulation in response to the components of culture medium 19 , When bacteria are grown in a rich medium like Luria Bertani LB broth, an FtsZ inhibitor would be activated to suppress the FtsZ assembly, resulting in the cell size having to increase in order to supply sufficient assembly-competent FtsZ; in contrast, when bacteria grow in a nutrient-poor source with a slow growth rate, the inhibitor would be in a low activation regime and bacterial cells subsequently live in a short-sized life.
We have investigated the details of bacterial adhesion on PET surfaces in an earlier publication 23 ; this study deals with the growth and detachment of the adherent Escherichia coli MG cells on PET in the presence of unlimited external nutrient sources.
PET is the substrate of choice since it is ubiquitous in food packaging 24 and widely used in cardiovascular implants e. Our study provides evidence regarding of the process of infection of surfaces in a nutritious environment e. Homogeneous PET films with a thickness of 0. Huntingdon, UK. The films were cut into many identical small pieces They were then dried with nitrogen. In order to prepare a required active synchronised bacterial suspension for our study, we followed the standard procedure: bacterial colonies of E.
Figure 2 illustrates the overall procedure for the measurement of E. Because continuous recruitment of new cells from the incubation medium onto surface may contribute to the count of bacteria on the substrates, the external medium in which the PET surfaces were incubated was refreshed each hour.
Our experimental procedure has followed the sequence of steps:. Schematic diagram illustrating the procedure to measure the amount of bacterial cells on PET surfaces per mm 2 i.
Each substrate sample was then placed vertically into a test tube diameter, 2. After each consecutive hour of incubation one of the plates was taken out for imaging Process III below , but all other remaining plates were subjected to the Process II again and placed into a new fresh culture medium tube. L to stain the cells with a fluorescent dye.
Process IV — we also need to monitor how many bacteria have detached from the substrate at each stage of development. After each surface specimen was removed from the LB culture medium at hourly intervals specified by j, the medium incubating this PET plate was immediately diluted by phosphate-buffered solution PBS.
For comparison between bacterial growth on surfaces and in the bulk medium, the stationary-phase synchronised E. In order to inhibit bacterial quorum sensing without directly killing bacteria or inhibiting their growth, MIC minimum inhibitory concentration was firstly determined. Briefly, bacterial suspension was diluted in LB as the inoculum. MIC minimum inhibitory concentration is defined as the lowest concentration of FC30 at which there was no detectable growth of E.
The tube for control contained 2. The brominated furanone dosage which was applied to incubate PET substrates would be the maximum concentration in the suspensions that showed the same OD as the control suspension. The bacterial growth on PET surfaces with the inhibition of quorum sensing was determined as illustrated in Fig. The statistics in our observation was acquired from two sources: in each microscopic image whether to count cells or to measure their size the field of view contained a large number of bacteria see Fig.
We have randomly chosen 20 independent fields of view for counting on each sample substrate. The whole experiment process, as illustrated in Fig. Live and dead cells are stained with green and red, respectively. In the meantime, we could tell that cells remaining on the surface dramatically increased in size, especially during the first hour. This is because the initial bacterial adhesion is reversible with a low barrier for desorption 6.
This represents the beginning of bacterial colonisation on the substrate. It is noteworthy that in this phase the average size of each cell in the multi-layer colonies underwent a clear decrease as colonisation progressed, whilst the single cells when they could be observed maintained the same size as in the stage ii.
We return to this issue in detail in the Discussion. The exponential regression fits in the log phase are shown for the bulk and substrate populations. The log-linear plot emphasizes the exponential growth of bacteria in clusters that appeared after the lag phase the error bars here and in other plots, are the standard deviation calculated from the large number of independent measurements at each data point.
Therefore, the stage of ii — iii could be regarded as the log phase of bacterial growth on PET surfaces. External nutrients were plentiful in our study the medium refreshed every hour and the exponential proliferation in clusters on surfaces is qualitatively the same as that of the log phase in a bulk medium.
The bulk value of doubling time corresponds well to the literature data Why was the doubling time of the sessile bacteria on substrates more than double than that of planktonic cells a term referring to free-swimming bacteria in the same culture liquid?
One possibility is that the bacteria needed more time to replicate at the solid-liquid interface, because only about half of their surface area could absorb the surrounding nutrition; at the same time, they needed to work harder to use their appendages to remain at the surface. Another reason might be the detachment of the daughter cells back into the bulk medium, which reduces the apparent count n j. Hence, the detachment of cells from surfaces over all three stages was investigated.
As seen in Fig. In fact, this is consistent with the necessary lag phase after a new cell detachment. We may thus conclude that the detachment of the daughter cells was not the reason for the slower bacterial growth on PET surfaces.
As demonstrated in the plots of N j and n j with increasing incubation time j, the dynamics of detachment appears to depend on the bacterial density on the surface. It could be seen in Fig. We interpret this as the result of gradually increasing the attachment strength of individual cells as they settle on the surface we discuss this in greater detail later in the text.
We interpret this as increasingly strong adhesion of bacteria to their neighbours as well as to the surface. This finding seems to demonstrate that the colonised bacteria were more likely to remain on the surface with the progressing colonisation. The results clarify the growth curve pattern of E. This growth curve appears to exhibit distinct phases: the lag and the exponential log phases, as with the conventional growth curve for bacteria in a bulk liquid medium. In addition to the adjustment of the number of bacteria and the bond strength with surfaces, the dimensions of the individual cells on PET surfaces also increased significantly after cultivation in a new environment, similar to the bacterial behaviour during the lag phase in a bulk medium.
In this stage, the cells that remain on the surface are metabolically active and synthesise the enzymes and factors needed to enter the next stage of cell division Note that the duration of the lag phase turns out to be the same for bacteria on the surface and the planktonic ones in the bulk of the same medium, as is clear from Fig. After the lag phase, an exponential growth of forming cell clusters was observed, stages ii — iii.
As the cells divided, the daughter cells spread outward and upward into clusters rather than occupying the entire surface area in a monolayer, which is consistent with the literature observations So what is the source of the greater numbers of single bacteria during the later stages of many dense micro-colonies?
One possibility might be the recruitment of planktonic cells from culture medium Another possibility is the migration or redistribution of the replicating cells on the substrate, which might be assisted by the motility of E. During the exponential growth phase, the bacterial generation time on PET surfaces was found to be much longer than that of free growing bacteria in the same culture medium. The results for the detachment over this period proved that this longer doubling time was not due to a loss of daughter cells from the surfaces into the medium, but instead to the less efficient cell division of sessile bacteria compared with that of planktonic cells in culture medium.
This is not difficult to understand, since in addition to the process of cell replication, some intracellular adenosine triphosphate ATP must be spent on bacterial anchoring at the interface; for instance, the assembly of fimbriae that aid in bacterial adhesion is at the expense of an energy cost In the traditional analysis of bacterial growth in bulk medium, dead cells are thought to appear because of the exhausted nutrients and the accumulation of waste materials, toxic metabolites and inhibitory compounds.
In our study this was different: the incubation medium was refreshed every hour, so that sufficient quantities of nutrients were always available during growth and toxin accumulation avoided.
Pogil activities for ap biology protein structure
Tuberculosis TB , caused by the intracellular pathogen Mycobacterium tuberculosis , remains one of the leading causes of mortality across the world. There is an urgent requirement to build a robust arsenal of effective antimicrobials, targeting novel molecular mechanisms to overcome the challenges posed by the increase of antibiotic resistance in TB. Mycobacterium tuberculosis has a unique cell envelope structure and composition, containing a peptidoglycan layer that is essential for maintaining cellular integrity and for virulence. The enzymes involved in the biosynthesis, degradation, remodelling and recycling of peptidoglycan have resurfaced as attractive targets for anti-infective drug discovery. Here, we review the importance of peptidoglycan, including the structure, function and regulation of key enzymes involved in its metabolism. We also discuss known inhibitors of ATP-dependent Mur ligases, and discuss the potential for the development of pan-enzyme inhibitors targeting multiple Mur ligases. Tuberculosis TB is a leading cause of mortality in the world today and is caused by the bacterial pathogen Mycobacterium tuberculosis.
The bacterium grows massively in fresh fecal matter under aerobic conditions for 3 days, but its numbers decline slowly afterwards. Cells are able to survive outside the body for a limited amount of time, which makes them potential indicator organisms to test environmental samples for fecal contamination. The bacterium can be grown and cultured easily and inexpensively in a laboratory setting, and has been intensively investigated for over 60 years. Under favorable conditions, it takes as little as 20 minutes to reproduce. During the staining process, E.
Bacterial growth, detachment and cell size control on polyethylene terephthalate surfaces
Cell size uniformity in healthy tissues suggests that control mechanisms might coordinate cell growth and division. We derived a method to assay whether cellular growth rates depend on cell size, by monitoring how variance in size changes as cells grow. Our data revealed that, twice during the cell cycle, growth rates are selectively increased in small cells and reduced in large cells, ensuring cell size uniformity. This regulation was also observed directly by monitoring nuclear growth in live cells.
To investigate the nature and origins of growth rate diversity in bacteria, we grew Escherichia coli and Bacillus subtilis in liquid minimal media and, after different periods of 15 N-labeling, analyzed and imaged isotope distributions in individual cells with Secondary Ion Mass Spectrometry. We find a striking inter- and intra-cellular diversity, even in steady state growth. This is consistent with the strand-dependent, hyperstructure-based hypothesis that a major function of the cell cycle is to generate coherent, growth rate diversity via the semi-conservative pattern of inheritance of strands of DNA and associated macromolecular assemblies.
Population Growth Vs. Replacement Reproduction vs.
Original Research ARTICLE
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