Microbial Nutrition, Ecology, and Growth

Transcription

1 Chapter 7 Microbial Nutrition, Ecology, and Growth Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

2 7.1 Microbial Nutrition Nutrition: process by which chemical substances (nutrients) are acquired from the environment and used in cellular activities Essential nutrients: must be provided to an organism Two categories of essential nutrients: Macronutrients: required in large quantities; play principal roles in cell structure and metabolism Proteins, carbohydrates Micronutrients or trace elements: required in small amounts; involved in enzyme function and maintenance of protein structure Manganese, zinc, nickel 2

3 Figure 7.1 Environmental conditions that influence microbial adaptations Gases: the atmosphere is a reservoir for nitrogen, oxygen, and carbon dioxide essential to living processes. Sunlight supplies the basic source of energy on earth for most organisms. Photosynthesizers can use it directly to produce organic nutrients that feed other organisms. Non photosynthetic organisms extract the energy from chemical reactions to power cell processes. Courtesy: Pacific Northwest National Laboratory Plant litter Soil microbes CO2 Nutrients Organic compounds Nutrients are constantly being formed by decomposition and synthesis and released into the environment. Many inorganic nutrients originate from non-living environments such as the air, water, and bedrock. Soil community Kathy Park Talaro Complex communities of microbes exist in nearly every place on earth. Microbes residing in these communities must associate physically and share the habitat, often establishing biofilms and other inter relationships. ph Acidic [H + ] Acid Neutral [OH ] Aquatic microbes Base Basic (alkaline) The acid or base content (ph) can show extreme variations from habitat to habitat. Microbes are the most adaptable organisms with regard to ph. C K The temperature of habitats varies to a significant extent among all places on earth, and microbes exist at most points along this wide temperature scale.

4 Microbial Nutrition Organic nutrients: contain carbon and hydrogen atoms and are usually the products of living things Methane (CH 4 ), carbohydrates, lipids, proteins, and nucleic acids Inorganic nutrients: atom or molecule that contains a combination of atoms other than carbon and hydrogen Metals and their salts (magnesium sulfate, ferric nitrate, sodium phosphate), gases (oxygen, carbon dioxide) and water 4

5 Chemical Analysis of Cell Contents 70% water Proteins 96% of cell is composed of 6 elements: Carbon Hydrogen Oxygen Phosphorous Sulfur Nitrogen Done to understand the cell s nutritional makeup 5

6 Forms, Sources, and Functions of Essential Nutrients Carbon-based Nutritional Types Heterotroph: must obtain carbon in an organic form made by other living organisms such as proteins, carbohydrates, lipids, and nucleic acids Autotroph: an organism that uses CO 2, an inorganic gas as its carbon source Not nutritionally dependent on other living things 6

7 Growth Factors: Essential Organic Nutrients Organic compounds that cannot be synthesized by an organism because they lack the genetic and metabolic mechanisms to synthesize them Growth factors must be provided as a nutrient Essential amino acids, vitamins 7

8 Classification of Nutritional Types Main determinants of nutritional type are: Carbon source: heterotroph, autotroph Energy source: Chemotroph gain energy from chemical compounds Phototrophs gain energy through photosynthesis 8

9 Nutritional Categories 9

10 Autotrophs and Their Energy Sources Photoautotrophs energy source is sunlight Oxygenic photosynthesis Anoxygenic photosynthesis Chemoautotrophs (lithoautotrophs) energy source is inorganic substances, such as hydrogen sulfide Methanogens, a kind of chemoautotroph, produce methane gas under anaerobic conditions Figure 7.2 Methanococcus jannaschii 10 Kathy Park Talaro

11 Heterotrophs and Their Energy Sources Figure 7.3 Extracellular Digestion in Bacteria and Fungi Majority are chemoheterotrophs Aerobic respiration Two categories Saprobes: free-living microorganisms that feed on organic detritus from dead organisms Opportunistic pathogen Facultative parasite Parasites: derive nutrients from host Pathogens (a) (b) (c) Organic debris Walled cell is a barrier. Enzymes Enzymes are transported outside the wall. Enzymes hydrolyze the bonds on nutrients. Some are obligate parasites 11 (d) Smaller molecules are transported across the wall and cell membrane into the cytoplasm.

12 7.3 Environmental Factors That Influence Microbes Niche: totality of adaptations organisms make to their habitat Environmental factors affect the function of metabolic enzymes Factors include: Temperature Oxygen requirements ph Osmotic pressure Barometric pressure 12

13 Adaptations to Temperature Three cardinal temperatures: Minimum temperature lowest temperature that permits a microbe s growth and metabolism Maximum temperature highest temperature that permits a microbe s growth and metabolism Optimum temperature promotes the fastest rate of growth and metabolism 13

14 Three Temperature Adaptation Groups Psychrophiles optimum temperature below 15 o C; capable of growth at 0 o C Mesophiles optimum temperature 20 o -40 o C; most human pathogens Thermophiles optimum temperature greater than 45 o C Figure 7.9 Ecological groups by temperature of adaptation Optimum Psychrophile Mesophile Thermophile Minimum Maximum Temperature C 14

15 Gas Requirements Oxygen As oxygen is utilized it is transformed into several toxic products: Singlet oxygen ( 1 O 2 ), superoxide ion (O 2 - ), peroxide (H 2 O 2 ), and hydroxyl radicals (OH - ) Most cells have developed enzymes that neutralize these chemicals: Superoxide dismutase, catalase If a microbe is not capable of dealing with toxic oxygen, it is forced to live in oxygen free habitats 15

16 Categories of Oxygen Requirement Aerobe utilizes oxygen and can detoxify it Obligate aerobe cannot grow without oxygen Facultative anaerobe utilizes oxygen but can also grow in its absence Microaerophilic requires only a small amount of oxygen Anaerobe does not utilize oxygen Obligate anaerobe lacks the enzymes to detoxify oxygen so cannot survive in an oxygen environment Aerotolerant anaerobes do not utilize oxygen but can survive and grow in its presence 16

17 Culturing by Oxygen Requirement Figure 7.12 Growth medium to determine oxygen requirements. +O2 -O2 usage by bacteria Figure 7.11 Culturing anaerobic bacteria Photo by Keith Weller, USDA/ARS Terese M. Barta, Ph.D.

18 Carbon Dioxide Requirement All microbes require some carbon dioxide in their metabolism Capnophile grows best at higher CO 2 tensions than normally present in the atmosphere Figure 7.11b. a CO2 incubator 18 Courtesy and Becton, Dickinson and Company

19 Effects of ph Majority of microorganisms grow at a ph between 6 and 8 (neutrophiles) Acidophiles grow at extreme acid ph Alkalinophiles grow at extreme alkaline ph 19

20 Osmotic Pressure Most microbes exist under hypotonic or isotonic conditions Halophiles require a high concentration of salt Osmotolerant do not require high concentration of solute but can tolerate it when it occurs 20

21 Miscellaneous Environmental Factors Barophiles can survive under extreme pressure and will rupture if exposed to normal atmospheric pressure 21

22 7.4 Ecological Associations Among Microorganisms Microbial Associations Symbiotic Organisms live in close nutritional relationships; required by one or both members. Nonsymbiotic Organisms are free-living; relationships not required for survival. Mutualism Obligatory, dependent; both members benefit. Commensalism The commensal benefits; other member not harmed. Parasitism Parasite is dependent and benefits; host harmed. Synergism Members cooperate and share nutrients. Antagonism Some members are inhibited or destroyed by others. 22

23 Ecological Associations Symbiotic two organisms live together in a close partnership Mutualism: obligatory, dependent; both members benefit Commensalism: commensal member benefits, other member neither harmed nor benefited Parasitism: parasite is dependent and benefits; host is harmed Figure 7.13 Satellitism, a type of commensalism Staphylococcus aureus growth Science VU/Fred Marsik/Visuals Unlimited Courtesy Arthur Hauck (Germany) Haemophilus satellite colonies 23

24 Interrelationships Between Microbes and Humans Human body is a rich habitat for symbiotic bacteria, fungi, and a few protozoa - normal microbial flora Types of relationships: commensal, parasitic, and synergistic relationships 24

25 Microbial Biofilms A Meeting Ground Biofilms result when organisms attach to a substrate by some form of extracellular matrix that binds them together in complex organized layers Dominate the structure of most natural environments on earth Communicate and cooperate in the formation and function of biofilms quorum sensing 25

26 Figure 7.14 Biofilm Formation and Quorum Sensing Chromosome Quorum-dependent proteins 1 Inducer molecule Matrix Free-swimming cells settle on a surface and remain there. Cells synthesize a sticky matrix that holds them tightly to the substrate. When biofilm grows to a certain density (quorum), the cells release inducer molecules that can coordinate a response. Enlargement of one cell to show genetic induction. Inducer molecule stimulates expression of a particular gene and synthesis of a protein product, such as an enzyme. Cells secrete their enzymes in unison to digest food particles. 26

27 7.5 The Study of Microbial Growth Microbial growth occurs at two levels: growth at a cellular level with increase in size, and increase in population Division of bacterial cells occurs mainly through binary fission (transverse) Parent cell enlarges, duplicates its chromosome, and forms a central transverse septum dividing the cell into two daughter cells 27

28 The Basis of Population Growth: Binary Fission Figure A young cell at early phase of cycle 2 A parent cell prepares for division by enlarging its cell wall, cell membrane, and overall volume. Midway in the cell, the wall develops notches that will eventually form the transverse septum, and the duplicated chromosome becomes affixed to a special membrane site. 3 The septum wall grows inward, and the chromosomes are pulled toward opposite cell ends as the membrane enlarges. Other cytoplasmic components are distributed (randomly) to the two developing cells. 4 The septum is synthesized completely through the cell center, and the cell membrane patches itself so that there are two separate cell chambers. 5 At this point, the daughter cells are divided. Some species will separate completely as shown here, while others will remain attached, forming chains or doublets, for example. Cell wall Cell membrane Chromosome 1 Chromosome 2 Ribsomes 28

29 The Rate of Population Growth Time required for a complete fission cycle is called the generation, or doubling time Each new fission cycle increases the population by a factor of 2 exponential growth Generation times vary from minutes to days Figure 7.16 Number of cells Number of generations Exponential value (a) (2 1) (2 2) (2 2 2) ( ) ( ) 5 Log of 3000 ( ) number Number 2500 ( ) of cells of cells using the power 1500 of (b) * Time *

30 Determinants of Population Growth The Viable Plate Count: Batch Culture Method Flask inoculated Samples taken at equally spaced intervals (0.1 ml) 500 ml 60 min 0.1 ml 120 min 180 min 240 min 300 min 360 min 420 min 480 min 540 min 600 min Sample is diluted in liquid agar medium and poured or spread over surface of solidified medium Plates are incubated, colonies are counted Number of colonies (CFU) per 0.1 ml Total estimated cell population in flask None <1* <10, , , , , , , , , ,150,000 *Only means that too few cells are present to be assayed.

31 Logrithm (10 n ) of Viable Cells Figure 7.18 The Population Growth Curve In laboratory studies, populations typically display a predictable pattern over time growth curve Stages in the normal growth curve: 1. Lag phase flat period of adjustment, enlargement; little growth Stationary phase The final outcome varies with the culture Hours T otal cells in population, live and dead, at each phase Few cells Live cells Dead cells (not part of count) 31

32 Logrithm (10 n ) of Viable Cells The Population Growth Curve Stages in the normal growth curve: 1. Lag phase 2. Exponential growth phase a period of maximum growth will continue as long as cells have adequate nutrients and a favorable environment Stationary phase The final outcome varies with the culture Hours T otal cells in population, live and dead, at each phase Few cells Live cells Dead cells (not part of count) 32

33 Logrithm (10 n ) of Viable Cells The Population Growth Curve Stages in the normal growth curve: 1. Lag phase 2. Exponential growth phase 3. Stationary phase rate of cell growth equals rate of cell death caused by depleted nutrients and O 2, excretion of organic acids and pollutants Stationary phase The final outcome varies with the culture Hours T otal cells in population, live and dead, at each phase Few cells Live cells Dead cells (not part of count) 33

34 Logrithm (10 n ) of Viable Cells The Population Growth Curve Stages in the normal growth curve: 1. Lag phase 2. Exponential growth phase 3. Stationary phase 4. Death phase as limiting factors intensify, cells die exponentially Stationary phase The final outcome varies with the culture Hours T otal cells in population, live and dead, at each phase Few cells Live cells Dead cells (not part of count) 34

35 Other Methods of Analyzing Population Growth Turbidometry most simple, use a spectrophotometer Degree of cloudiness, turbidity, reflects the relative population size Figure 7.19 Percent of light transmitted (1) Kathy Park Talaro/Visuals Unlimited (a) (b) (2) T ~ A or T ~ A 35