Lecture notes for week 4
Lecture notes for week 4 BIOL 2460-001
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This 11 page Class Notes was uploaded by Mercy on Tuesday October 6, 2015. The Class Notes belongs to BIOL 2460-001 at University of Texas at Arlington taught by Dr. Michelle Badon in Summer 2015. Since its upload, it has received 127 views. For similar materials see Nursing Microbiology in Biology at University of Texas at Arlington.
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Date Created: 10/06/15
Lecture Notes Week 4 Tuesday September 29 2015 0759 Pay attention to words in bold and italics Bacteria and Archaea Difference between B and A alike but chemical make up is different no peptidoglycan Bacteria are everywhere they are your microbiota These compatriots are vital to your health These org helps to digest food to producing vitamins and amino acids to stimulating the immune system to protecting you from harmful pathogens to even having an influence on your behavior The gut microbiota is a complex ecosystem comprised of numerous genera including Bacteroides Clostridium Streptococcus Lactobacillus Bifidobacterium and other Biofilms is a community of microbes living together associating together Bacteria does not exist in a Planktonic singlecell form History Bacteria have been for 35 38 billion years Bacteria Gracilicutes Bacteria with Gram Negative cell wall eg Ecoli Firmicutes Bacteria with Gram Positive cell wall eg Bacillus Tenericutes Bacteria without a cell wall Mendosicutes Archaebacteria have no peptidoglycan can survive in extreme environment most primitive forms of life not considered medically important but are economic important Microbial Morphology size shape and arrangement Size size affects its biological properties one of which is the rate of nutrient uptake and waste elimination transport rates is a function of the membrane surface area and cell volume surface to volume ratio a small cell has a greater surface volume ratio than a larger cell greater surface area to service a smaller volume a smaller cell has a faster metabolic rate This means that small cell can grow faster adapt to environmental changes quicker and achieve greater population densities than a larger eukaryotic cell Shapes morphology There are roughly 7 general shapes of Bacteria Coccus cocci plural Greek word for berry are spherical in shape Bacillus bacilli Latin for little staff are rod shaped Spirillum spirilli Latin for little coil are rigid curved or spiral shaped cylinder Vibrio vibrios are gently curved rods Spirochete spirochetes Greek for coil of long hair are slender flexible spirals Filamentous form long multinucleated filaments or hyphae that may branch to produce mycelium Ex Actinomycetes Pleomorphic Bacteria that are variable in shape and cannot be characterized by a single form Most pleomorphic bacteria assume a general rod shaped form different form bacillus morphology These also include bacteria that assume squares star shapes and coccobacilli Arrangement Bacteria are generally characterized by the way the cells are grouped of arranged Arrangements of cocci diplococci a pair of cocci or two cocci streptococci are chains of 3 or more cocci tetrads are four cells or cocci sheets are multiple divisions on two planes cube are packets of 8 cocci staphylococci are multiple divisions in three planes to form irregular clusters Arrangement of Bacilli Most bacilli are not found in special arrangements although a few species will form Diplobacillus Streptobacillus Palisades side by side arrangements The Prokaryotic Cell The Bacteria most have rigid cell walls Peptidoglycan contained within the cell wall of the bacteria identifying whether a bacteria is gram positive or gram negative it is not found in Archaea or the Eukarya Multiply by binary fission one cell divides into two daughter cells Move by flagella Archaea have the same shape size and appearance as the Bacteria Multiply by binary fission moves by flagella have rigid cell walls cell wall composition differs from that of the bacteria they do not have peptidoglycan as part of their cell walls they have ability to grow in extreme environment in which most organisms cannot Prokaryotes Prokaryotic Cell PC are bound by a chemically complex cell wall and separated from it by a periplasmic space lies the plasma membrane PC does not contain internal membrane bound organelles it39s interior appears morphologically simple both gram and gram cells can use flagella for locomotion many cells are surrounded by a capsule or slime layer external to the cell wall Genetic materials is located in the nucleoid and is not separated from the surrounding cytoplasm by membranes Ribosomes and larger masses called inclusion bodies are scattered about in the cytoplasmic matrix cells are much simpler than eukaryotic cells External structures Appendages structure sprout from the surface of bacteria common but are not present on all species two groups motility flagella and axial filaments and attachments or channels fimbriae and pili Flagellum flagella cannot be seen with the light microscope unless a specialize staining procedure is used is a slender rigid rod organelles of motility or self propulsion cells swim freely through an aqueous environment composed of 3 parts filament hook and basal body Filaments is a rigid helical rod that extends from the surface of the cell to the tip of the flagellum and acts like a propeller It is composed of multiple protein subunits called flagellin Hook anchored to the cell by the basal body Basal body is essentially a rod that spans the cell wall and passes through a series of rings t anchors the flagellum within the cell membrane and serves as a motor to rotate the filament Not all bacteria are motile non motile bacteria especially cocci do not possess flagella Flagella vary both in no and arrangement Polar Arrangement the flagella are attached at one or both ends of the cell 3 subtypes of polar arrangements 1 Monotrichous mono means one and trichous means hair cells with one single polar flagellum 2 Lophotrichous lopho means tuftcluster cells with a tuft or small bunches of flagella 3 Amphitrichous amphi means on both sides cells with a single flagellum at both ends of the cell Non Polar arrangement Peritrichous peri means around cells with flagella all over the surface of the cell Chemotaxis a type of behavior seen by flagellated bacteria detect and move in response to chemical signals Positive chemotaxis movement toward chemical attractants nutrient Negative chemotaxis movement away from repellents potentially harmful compound Bacteria do not always swim aimlessly but are attracted by sugars and amino acids and are repelled by harmful substances and bacteria waste products they also respond to other environmental cues such as temperature light and gravity Fimbriae are short fine hairlike structure that are thinner than flagella and not involved in motility used by bacteria to attach to surfaces smaller and more numerous than flagella and can only be seen with the electron microscope only found in the Gram Negative Bacteria A fimbria is a straight cylinder composed of protein subunits call pilin at the tip of each fimbriae is a protein called an adhesion which recognizes and binds to specific receptors on a host cell surface a the primary function is to facilitate attachment Sex Pilus the structures that mediate conjugation are called sex pili and differ from the standard fimbriae in that they are genetically encoded by sex factors or conjugative plasmids found only in Gram negative pili are also longer than fimbriae and much less abundant only one or two pili are found on the cell surface Capsule is a layer of mucoid material that surrounds the bacterial cell lying outside the cell wall when this mucoid layer is thick well organized and difficult to remove it is called a capsule Capsule is a thick structured layer that is not readily removed if it is thin diffuse and easy to wash off it is called slime layer Slime layer is a loose structure that is easily washed off difference between a capsule and a slime layer most capsules are composed of a network of polysaccharide fibers that have been secreted from the cell called the glycocalyx surface coating the amount of capsule produced by a cell depends on the culture conditions Growth in high carbon low nitrogen medium promote capsule formation General functions of a capsule or slime layer resist desiccation they contain a great deal of water protection and help the bacteria adhere to surfaces prevent or inhibit phagocytosis by host phagocyte Encapsulated bacteria have a greater pathogenicity because capsules protect against phagocytes help to prevent infection streptococcus pneumoniae cause of pneumonia an infection in the lung When it lacks a capsule it is destroyed easily and does not cause disease When capsulated quickly kills mice Haemophilus influenzae causes meningitis Bacillus anthracis cause of anthrax S Layers common in Archaea where they may be the only wall structure outside the plasma membrane are single layers of thousands of copies of a single protein linked together like tiny chain mail They are often called the armor of a bacterial cell Bacterial cells protect themselves with either an S layer or a glycocalyx or both it took scientists a long time to discover them because bacteria only produce them when they are in a hostile environment two bacteria that have the ability to produce S layer they are Clostridium difficile and Bacillus anthracis some bacteria use S layers to aid in attachment n gram negative bacteria it adheres directly to the outer membrane In gram positive bacteria it is associated with the peptidoglycan surface Functions may protect cell against ion and pH fluctuations osmotic stress enzymes or predacious bacterium serves as a permeability barrier to large molecular weight compounds may also confer some type of protection against host defense mechanisms to many pathogenic bacteria helps to maintain the shape and envelope rigidity of some bacterial cells can promote cell adhesion to surface Cell envelope lies outside the cytoplasm composed of two or three layers cell wall cell membrane outer membrane two layers in gram positive cell wall and cell membrane three layers in gram negative cell wall cell membrane and outer membrane function as a single protective unit Cell wall the cell wall is a rigid structure that surrounds the bacterial cell just outside of the plasma membrane functions gives the bacterium its shape gives strong mechanical strength to the cell and protects it from exploding or bursting due to osmotic pressure and lysis Shape and strength due to the peptidoglycan many bacteria have cell walls that contain compounds that contribute to the virulence of that organism the bacterial cell wall is also the site of action of several antibiotics most notably the betalactamase family which includes penicillin Penicillin prevent cell wall synthesis Penicillin and other drugs are effective because they target and break the tetrapeptide crosslinks in the peptidoglycan bridge extending from the NAM Nacetyl muramic acid residues More effective against gram positive than gram negative the outer membrane prevents the medication from reaching its site of action the peptidoglycan layer The substrate for enzymes such as lysozyme provide a natural defense against certain bacteria Lysozyme degrades the cell wall by breaking the beta 14 bonds that connect the NAM and NAG Nacetyl glucosamine subunits These compounds attack the cell wall and cause bacteria to lyse Penicillin and its relatives named for the parent compound is large diverse group of compounds most of which end in the suffix cuin penicillin could be completely synthesized in the laboratory from simple raw materials it is more practical and economical to obtain natural penicillin through microbial fermentation o the natural product can be used either in unmodified form or to make semisynthetic derivatives Penicillium chrysogenum is the major source of the drug Penicillin G and V are the most important natural forms is considered the drug of choice for infections by known sensitive grampositive cocci most streptococci and some gram negative bacteria meningococci and the syphilis spirochete Penicillinaseresistant penicillins such as methicillin nafcillin and xacillin are used in treating infections caused by some penicillinaseproducing bacteria Cell wall composition the cell wall of a eubacteria is composed of a unique polymer called peptidoglycan that is not found in the archaebacteria nor the eukaryotes Peptidoglycan or murein is a linear polymer of alternating subunits of Nacetyl glucosamine NAG and N acetyl muramic acid NAMbackbone know the difference between these two and what they are A side chain of four amino acids is attached to each NAM subunit the side chains of linked peptidoglycan units are joined together through a peptide interbridge that forms covalent bonds between the tetrapeptide side chains provides much of the strength and rigidity possessed by bacterial cell walls most gram negative do not utilize a peptide interbridge they will simply form covalent bonds between specific residues of adjacent tetrapeptide side chains Drugs that affect the bacterial cell wall The cell walls of most bacteria contain a rigid peptidoglycan which protects the cell against rupture from hypo environments Active cells must constantly synthesize peptidoglycan and transport it to its proper place in the cell envelope drugs such as penicillins and cephalosporins react with one or more of the enzymes required to complete this process causing the cell to develop weak points at growth sites and to become osmotically fragile Bactericidal antibiotics that produces this effect because the weakened cell is subject to lysis it is essential to note that most of these antibiotics are active only in young growing cells because old inactive or dormant cells do not synthesize peptidoglycan Differences between a gram positive and gram negative bacteria G has a thick peptidoglycan and cell wall while 6 has a thin peptidoglycan outer membrane and plasma membrane Gram positive cell wall is a single layer that is 2080 nm thick and makes up 5090 of the dry weight of the cell primarily composed of peptidoglycan containing a peptide interbridge it does not possess an outer membrane it usually contains large amounts of negatively charged teichoic acids which helps to give the bacteria its negative charge and may be important in maintaining the strength of the wall Teichoic acids are polymers of glycerol or ribitol joined by phosphate group embedded in the peptidoglycan They are not found in the gram negative bacteria They are connected to either the peptidoglycan itself or to plasma membrane lipids lipoteichoic acids Teichoic acids give the cell its negatively polarity Gram negative cell wall more complex than the gram positive cell wall has a single peptidoglycan layer that is about 13 nm thick thin compared to 6 and makes up 520 of the dry weight of the cell there is an outer membrane that lies outside of the thin peptidoglycan layer embedded with proteins called Braun39s Lipoprotein Braun39s Lipoprotein most abundant membrane protein It is covalentlyjoined to the peptidoglycan and embedded in the outer membrane The peptidoglycan and the outer membrane are firmly linked by this protein Adhesion site strengthens the wall and holds the outer membrane in place It is proposed that substances can move into the cell through these adhesion sites rather than through the periplasm Regions of direct contact or possibly true membrane fusions Peptidoglycan layer is covered by an outer membrane that contains various proteins as well as lipopolysaccharides LPS Lipopolysaccharides LPS is a large complex molecule containing both lipids and carbohydrates It consists of 3 parts Lipid A consist of 2 glucosamine sugar derivatives each attached to 3 fatty acids and phosphate The lipid A residue is buried within the outer membrane and the remaining components are projected from the cell surface Core polysaccharide consists of 10 sugar residues most of which have an unusual structure and are attached to the lipid A moiety Oside chain LPS structure ends with a terminal 0 side chain The 0 antigen is a short polysaccharide chain that varies in composition and generally contains a number of unusual sugar residues LPS importance is negatively charged an contributes to the overall negative charge of the cell like the teichoic acids of 6 cells the lipid A molecule is toxic and serves as a superantigen to induce an inflammatory immune response endotoxin Endotoxin stimulates fever and shock reactions in G infections such as meningitis and typhoid fever Teichoic acids are the major antigens of 6 cells LPS are the major antigen of 6 cells Outer membrane function functions as a permeability barrier that protects the cell from a number of toxic agents including some dyes and several antibiotics more permeable than plasma membrane and permits the passage of small molecules like glucose due to porins contains a number of protein channels called porins that make the lipid bilayer relatively permeable to small molecules 3 porins molecules band together to form narrow channels through which smaller molecules can pass Blocking the entrance of harmful chemicals and certain antibiotics Non typical cell walls several bacterial groups lack the cell wall stucture of gram negative or positive bacteria and some have no cell wall at all Mycobacterium and Nocardia contain peptidoglycan and stain grampositive but the bulk of their cell wall is composed of unique types of lipids One of these is a verylongchain fatty acid called mycolic acid or cord factor that contributes to the pathogenicity The Archaea the other prokaryotes single celled and a simple organisms more closely related to Domain Eukarya than bacteria For example archaea and eukaryotes share a number of ribosomal RNA sequences that are not found in bacteria and their protein synthesis and ribosomal subunit structures are similar exhibit unusual and chemically distinct cell walls in some the walls are composed almost entirely of polysaccharides and in others the walls are pure protein but as a group they all lack the true peptidoglycan structure Live in the most extreme habitats in nature For this reason they are often called extremophiles meaning that they quotlovequot extreme conditions in the environment Metabolically the archaea exhibit incredible adaptations to what would be deadly conditions for other organisms They have adapted to multiple combinations of heat salt acid pH pressure and atmosphere Included in this group are methane producers hyperthermophiles extreme halophiles and sulfur reducers Mycoplasmas and other cellwalldeficient bacteria are bacteria that naturally lack cell wall the mycoplasma cell membrane is stabilized by sterols and is resistant to lysis these extremely tiny pleomorphic cells are very small bacteria ranging from 01 to 05 tim in size The most important medical species is Mycoplasma pneumoniae which adheres to the epithelial cells in the lung and causes an atypical form of pneumonia in humans Cell membrane or plasma membrane or cytoplasmic membrane it is a thin structure 510 nm thick that completely surrounds the cell and can only be seen with an Electron Microscope selectively permeable barrier that prevents cytoplasmic contents from leaking out of the cell nutrient uptake waste transport and protein mechanical boundary of the cell retains the cytoplasm secretion or discharge of metabolic products into the external environment movement of substances across the membrane detection of environmental cues for chemotaxis location of many metabolic processes such as respiration photosynthesis and the synthesis of lipids and cell wall constituents enzymes it is composed of 2 layers of phospholipid molecules that is commonly called lipid bilayer Phospholipid Lipids containing a substituted at least one phosphate group often a nitrogenous constituent and two fatty acid chains on a glycerol backbone The third glycerol hydroxyl is joined with a phosphate group and ethanolamine is attached at the phosphate making up 30 40 of membrane mass Phosphatidyl ethanolamine is an important phospholipid frequently present in bacterial membrane Lipid waterinsoluble organic molecules important in the structure of the cytoplasmic membrane and in the cell wall the polar head of each phospholipid molecule is hydrophilic water loving the nonpolar tails fatty acids of the phospholipids are hydrophobic water fearing The membrane is additionally stabilized by divalent cations such as Mg2 and Ca2 which interact ionically with the negatively charged phospholipids It is important to emphasize that the cytoplasmic membrane is not a rigid structure but is very dynamic and fluid like One of the major differences between prokaryotic and eukaryotic membranes is that prokaryotic membranes do not contains sterols such as Cholesterol Sterols are rigid planar molecules that generally make up 525 of an eukaryotic membrane Sterols strengthen the membrane and make it less flexible this is needed because most Eukaryotic cells do not have a rigid cell wall Some bacterial membranes contain a sterol like compound called hopanoids that serve a similar function stabilize the membrane Fluid Mosaic Model By 5 Jonathan Singer and Garth Nicholson This model distinguishes between two different types of proteins Various proteins are inserted into the phospholipid bilayer Peripheral protein loosely connected to the membrane and can be easily removed soluble in aqueous solutions make up 2030 of total protein do not span both layers Integral proteins span the bilayer and are arrayed on both the internal and external surface not easily extracted from membranes and are insoluble in aqueous solutions when freed of lipids are typically amphipathic structurally asymmetric with polar and nonpolar ends The integral protein has a variety of functions Many serve to transport nutrients into the cell or toxic products out of the cell Many of these proteins are biosynthetic enzymes that are required for synthesis of the cell wall Some of the proteins are components of the cells energy generating machinery such as the electron transport chain c The plasma membrane is essential to the survival of microorganisms Antimicrobial Drugs That Disrupt Cell Membrane Function A cell with a damaged membrane invariably dies from disruption in metabolism or lysis and does not even have to be actively dividing to be destroyed The antibiotic classes that damage cell membranes have specificity for particular microbial groups based on differences in the types of lipids in their cell membranes Polymyxins interact with membrane phospholipids distort the cell surface and cause leakage of proteins and nitrogen bases particularly in gramnegative bacteria The polyene antifungal antibiotics amphotericin B and nystatin form complexes with the sterols on fungal membranes these complexes cause abnormal openings and seepage of small ions The universal presence of membranes in microbial and animal cells alike means that most of these antibiotics can be quite toxic to humans Transport systems simple diffusion process by which some molecules move freely into and out of the cell ex water small hydrophobic molecules gases Facilitated diffusion moves impermeable compounds from one side of the membrane to the other over a concentration gradient Molecules are transported until the concentration is the same on both sides of the membranes It is also known as Passive transport Active transport can accumulate compounds against a concentration gradient It requires an expenditure of energy Group Translocation transport process that chemically alters a molecule during its passage through the cytoplasmic membrane Internal structures Cytoplasm cytoplasmic matrix is a single compartment that does not contain mitochondria chloroplasts Endoplasmic reticulum cytoplasmic streaming microfilaments or microtubules unlike the eukaryotic cell the PC cytoplasm does not contain membrane bound organelles the cytoplasm is a viscous liquid that is enclosed by the cell membrane it lies between the plasma membrane and the nucleoid Most of the biological functional that are necessary to sustain life occur in the cytoplasm Composed of approximately 70 80 water the remaining 20 includes the nucleoid DNA ribosomes for protein synthesis more than 1500 catabolic and anabolic enzymes carbohydrates lipids amino acids and inorganic ions Mesosomes internal membrane system are invaginations of the plasma membrane in the shape of vesicles seen in both 6 and G mostly in G may be involved in cell wall formation during division or play a role in chromosome replication and distribution to daughter cells Nucleoid irregular shaped region of genetic material DNA other names nuclear body chromatin body and nuclear region common single circle of double stranded deoxyribonucleic acid DNA some have linear DNA chromosomes DNA is looped and coiled extensively Drugs that affect Nucleic acid synthesis Antimicrobial drugs interfere with nucleic acid synthesis by blocking synthesis of nucleotides inhibiting replication or stopping transcription Because functioning DNA and RNA are required for proper translation as well the effects on protein metabolism can be farreaching Other antimicrobials that inhibit DNA synthesis are Chloroquine an antimalarial drug binds and crosslinks the double helix The newer broadspectrum quinolones inhibit DNA unwinding enzymes or helicases thereby stopping DNA transcription Antiviral drugs that are analogs of purines and pyrimidines including azidothymidine AZT and acyclovir insert in the viral nucleic acid and block further replication Plasmids double stranded DNA molecules can exist and replicate independently of the chromosomes or may be integrated with it present in many bacteria alone with chromosomes inherited or passed on to the progeny not required for host growth and reproduction can render bacteria drug resistant and give them new metabolic abilities make them pathogenic often move between bacteria and can confer properties throughout an entire population they are not usually attached to the plasma membrane Ribosomes site of protein synthesis found in the cytoplasm loosely attached to the plasma membrane made of protein and RNA ribonucleic acid make proteins for transport outside the cell ribosomes synthesize to remain within the cell Antimicrobial Drugs That Block Protein Synthesis Most are inhibitors of translation or protein synthesis react with the ribosomemRNA complex The ribosomes of eukaryotes are different in size and structure from those of prokaryotes so antimicrobials usually have a selective action against bacteria One potential consequence of such drugs is the damage they can do to eukaryotic mitochondria which contain a prokaryotic type of ribosome Aminoglycosides streptomycin gentamicin for example insert on sites on the 305 subunit and cause the misreading of the mRNA leading to abnormal proteins Tetracyclines block the attachment of tRNA on the A acceptor site and effectively stop further synthesis Other antibiotics chloramphenicol attach to sites on the SOS subunit in a way that prevents the formation of peptide bonds or some erythromycin inhibits translocation of the subunit during translation Prokaryotic Ribosomes Involved in protein synthesis and they are the structures that are intimate in the joining of Amino Acids Cytoplasmic inclusion bodies used for storage It stores nutrients intracellularly when nutrients are abundant and is used when nutrient become depleted Granules of materials starch glycogen polyhydroxybutyrate PH B sulfur and polyphosphate cellular C S and O reserve materials are present in the cytoplasm Periplasmic Space PS The periplasmic space refers to a gap that exists between the cell membrane and the outer membrane that is clearly visible in electron micrographs of gram negative cells It is rarely seen in GM positive cells and the gap is smaller The periplasm is a gel like substance that fills the periplasmic space in G bacteria and is contained in the cell wall layer of 6 bacteria G cells may have periplasm even if it lacks an obvious PS The periplasm contains numerous digestive enzymes transport proteins osmoprotectants etc The Cytoskeleton Until very recently scientists thought that the shape of all bacteria was completely determined by the peptidoglycan layer cell wall Although this is true of many bacteria particularly the cocci other bacteria produce long polymers of proteins that are very similar to eukaryotic actin Cytoskeleton in bacteria are arranged in helical ribbons around the cell just under the cell membrane Fibers contribute to cell shape perhaps by influencing the way peptidoglycan is manufactured and also function in cell division The fibers have been found in rodshaped and spiral bacteria They are composed in part of proteins unique to bacterial cells making them a potentially powerful target for future antibiotic development Endospore spore know for the exam a special resistant dormant structure formed by both gram positive and gram negative bacteria that can survive and withstand hostile conditions those formed by gram positive are of medical importance Medical significance of Bacterial spores Although the majority of endosporeforming bacteria are relatively harmless several bacterial pathogens are endospore formers Bacillus anthracis is the agent of anthrax its persistence in endospore form makes it an ideal candidate for bioterrorism The genus Clostridium includes even more pathogens C tetani the cause of tetanus lockjaw C difficile the cause of pseudomembranous colitis C perfringens the cause of gas gangrene When the endospores of these species are embedded in a wound that contains dead tissue they can germinate grow and release potent toxins another toxinforming species C botulinum is the agent of botulism a deadly form of food poisoning because they inhabit the soil and dust endospores are constant intruders where sterility and cleanliness are important they resist ordinary cleaning methods that use boiling water soaps and disinfectants and they frequently contaminate cultures and media several endosporeforming species cause food spoilage or poisoning Ordinary boiling 100 C will usually not destroy such endospores so canning is carried out in pressurized steam at 120 C for 20 to 30 minutes Such rigorous conditions ensure that the food is sterile and free from viable bacteria spore has 2 phase life cycle vegetative and endospore The vegetative cell c is a metabolically active and growing entity that can be induced by environmental conditions to undergo spore formation or sporulation the depletion of nutrients especially an adequate carbon or nitrogen source is the stimulus for a vegetative cell to begin endospore formation Bacterial endospores are the hardiest of all life forms their survival under such harsh conditions is due to several factors extraordinarily resistant to environmental stresses heat ultraviolet radiation gamma radiation desiccation freezing chemical disinfectants The heat resistance of spores has been linked to their high content of calcium and dipicolinic acid although the exact role of these chemicals is not yet clear The autoclave is important in microbiology because endospores often survive boiling for an hour or more CSI BACTERIA Crime scene investigators looked for patterns of specific bacteria left behind by suspects instead of fingerprints Noah Fierer at the University of Colorado Boulder studied the variability in bacterial communities on human fingertips and found that this scenario isn t as unlikely as you may think Fierer and his colleagues took samples from computer keyboards and computer mice analyzed the bacterial DNA from the samples and came up with a bacterial fingerprint that could be matched to the individual that had used the keyboard or mouse
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