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University of Otago
Keith Ireton

PHCY219 – Microbiology Section 1 – Lecture 2 Judith Bateman Lecture 2 – Microbial Growth Objectives 1.Describe microbial growth and process of binary fission Microbial growth refers to the growth of the population (# in the colony) rather than the size of the individual cell. Need to know this diagram for the first objective of the lecture. This top rod cell is called the parent cell Duplication of bacterial chromosome can be seen in the second part of the diagram The bacteria make more cell wall and form the septum. From the diagram we can also see that the DNA migrates. The cell divides. Now there are two separate cells (two daughter cells)! Binary fission complete. This diagram represents binary fission of coccyl (spherical) bacteria. It demonstrates that this type of division can lead to a great increase in population number. Refer to table. 1 | P a g e PHCY219 – Microbiology Section 1 – Lecture 2 Judith Bateman Generation mean time = how long it take the division process to finish (i.e. – time it takes for a cell to divide) - Generation mean time varies for different species. For example, E. coli takes 20 minutes whereas M. tuberculosis takes a whole day! We can plot the growth on a graph, however because the growth is exponential, it can be difficult to graph with a linear scale. So we use logarithmic scale instead. The division plane is important because it dictates the cell arrangement  If plane of division is in the same plane it makes a chain.  If the plane of division is in many planes that the result will be a cluster of bacteria 2 | P a g e PHCY219 – Microbiology Section 1 – Lecture 2 Judith Bateman Growth Requirements - Physical Factors o Gaseous Atmosphere Definitions (memorise these!) Aerobes These organisms need oxygen In the electron transport chain, the terminal electron acceptor is oxygen Anaerobes They like to live in places where there is an absence of oxygen Their final electron acceptor in the electron transport chain is NOT oxygen. It is exogenous e.g. – nitrate & sulphate NOTE: Fermentation  absence of electron transport chain. Facultative Anaerobes They can grow with or without (but they don’t grow as well without oxygen). Indicates that they might have two different ways of metabolism to survive. Microaerophiles These organisms like to live in areas where there is oxygen but not too much Capnophiles An abundance of carbon dioxide is needed for capnophiles to grow. This diagram illustrates that different microbes have different requirements for oxygen. We can tell by the different distributions along the column. If there is a dense distribution near the top then it’s likely that they need oxygen. Conversely if the organisms are packed at the bottom, then operate in the absence of oxygen. This is why some blood cultur
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