1	BACTERIA & ARCHAEA These small (typically 1 micrometer) cells have the potential for rapid population growth. Bacterial diseases have been effectively controlled thru public health.
2	Reading Assignment For lectures 7 and 8 read Chapter 27 up to section 27.4. Read the Box 27.2 on lateral gene transfer (p.602). Read the Essay, “Antibiotics and the evolution of drug resistance” (p. 604) and think about its implications.
3	Exciting Developments 1) The Domain ARCHAEA was discovered in the last 30 years (at the University of Illinois (UIUC) by Prof. Carl Woese). 2) Direct Sequencing has revealed many new species that have never been grown in culture. 3) In Bacteria and Archaea genes move from one species to distant species (horizontal gene transfer) fairly frequently.
4	Characteristics of DOMAINS
5	Relationships of the three Domains
6	Horizontal Gene Transmission Genes are transmitted from parent to offspring. The continuity over generations is called vertical transmission. Genes that are common in one lineage (insects) sometimes are found in other lineages (cat). The reasonable interpretation is that the piece of DNA moved between lineages. Such a movement is call horizontal transfer. After a horizontal transfer event the gene is transmitted in the usual (=vertical) way.
7	Gene Transfer between species Genetic engineering is based on moving genes from one species into another. We should not be surprised that the process has worked in evolution. When the phylogeny of gene A does not match the phylogeny of most other genes in the species, one may suspect that gene A entered from another lineage.
8	DIRECT SEQUENCING DNA sequences can be amplified from a sample without first culturing the organisms. Many ‘species’ have been discovered that have never been cultured. Archaea, originally thought to be limited to extreme environments, have proved to be common in soil, but remain difficult to culture.
9	Culturing microorganisms Before sequencing we had to be able to grow (culture) the microorganism in the laboratory. One of the common ways to grow bacteria is on a nutrient gel in a petri dish. The ‘daughters’ of the original cell do not move much and the population (colony) becomes visible as a dot (spot) on the gel.
10	Reproduction in Bacteria is normally by binary cell division A cell dividing into two cells after a period of growth (increase in mass) is the most common form of reproduction, getting more individuals in the population. When a cell divides into two approximately equal sized daughters it is called binary cell division.
11	Cell Division Increases Cell Number
12	Doubling time The interval between cell divisions is called the doubling time as well as the length of the cell cycle. Smaller cells generally have shorter doubling times. Escherichia coli, a common bacteria, has a doubling time as short as 20 minutes.
13	Population Growth A constant doubling time leads to a pattern of exponential growth. Exponential growth and geometric growth are two expressions of the same pattern. Exponential growth assumes time is continuous. Geometric models assumes an integer number of time intervals, e.g. hours, days, years.
14	Models of Population Growth Discrete or Geometric N_t+1 = l• N_t Continuous or Exponential N_t = N₀•e^r•t
15	More on population growth N_{in future} = N_initial•2^{time elapsed/doubling time} is another formula for population growth. A single E. coli cell could have 2^{24hr•3doublings per hour} =2⁷² = 4.72•10²¹ descents in 24 hours and 9•10⁴² in 48 hrs. The very large population sizes are not possible, because each cells requires a minimal amount of limited resources.
16	Microbial Growth in Batch Cultures The “batch” is an unexploited resource. Cell(s) arrive in an environment with resources. After a lag during which they ‘crank up’ the enzymes needed for growth, they grow at their maximum rate until they exhaust the resources necessary for growth (energy & materials). Cells go into shutdown mode and eventually die (except those that are able to get to a new “batch”).
17	The Cultural Growth Cycle Lag Exponential Stationary Decline Death
18	Graphing Population Growth If a population is growing exponentially, graphing the log (or ln) of N (y axis) versus time (x axis) will be a straight line. ‘Straightness’ is an attribute effectively evaluated by ‘eye’ and also by mathematical procedures. Many graphs of population growth present the log of N rather than N.
19	METABOLIC DIVERSITY of Bacteria and Archaea SOURCES OF ENERGY Light Reduced organic molecules Reduced inorganic molecules SOURCES OF CARBON Inorganic =CO₂ & CO₃^-& CH₄ (Autotrophs) Reduced organic compounds (Heterotrophs)
20	SYMBIOSIS Many protists, plants and animals have bacteria (and Archaea?) that live inside of them that do much of the metabolic work. Rhizobium, a bacterial symbiont of legumes (Bean family) is able to ‘fix’ nitrogen (take N from atmosphere and reduce it to a form plants can use).
21	Problem Using the log scale for population size on the Y axis and years on the X axis, graph the following values of population size on consecutive years; 1, 3, 8, 25, 81, 250, 700, 800, 900, 1000 What would you say about your graph?
22	Vocabulary Archaea Batch culture Cultural growth cycle Direct sequencing Doubling time Geometric growth Horizontal transfer Log growth Nitrogen fixation Rhizobium Symbiosis Lineage