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Transcript
28.1 The Microbial World • Bacteria were described as early as the 17th century • Louis Pasteur used microbes to discredit the theory of spontaneous generation in 1659 • Microbiology includes the study of bacteria, archaea, protists, and some fungi Pasteur’s Experiments 28.1 The Microbial World • Many microbes provide important benefits – Normal flora on our bodies – Ecosystems • Decomposers (bacteria and fungi) • Photosynthesis (cyanobacteria and some protists) – Industry • Food processing • Medicine • Biotechnology 28.2 Bacteria and Archaea 28.1 The Microbial World • Typical Bacteria Cell – Bacteria can be categorized based on their cell wall • Gram positive • Gram negative 28.2 Bacteria and Archaea • Bacterial Reproduction – Binary Fission: a bacterial cell replicates its genome and divides in half (asexual reproduction) – In harsh conditions, some bacteria can form a resistant endospore (not a reproductive strategy) – No sexual reproduction, but three mechanisms of genetic recombination • Conjugation: “male” cell passes DNA to “female” through a sex pilus • Transformation: bacterium takes up DNA from environment released by dead bacteria • Transduction: viruses carry bacterial DNA from cell to cell Binary Fission 28.2 Bacteria and Archaea • Bacterial Metabolism – Most are Heterotrophic • Some are anaerobic and cannot use oxygen as final electron acceptor – Sulfate reducers-transfer electrons to sulfate – Denitrifying bacteria use nitrate – Some are chemosynthetic • Reduce carbon dioxide to an organic compound using electrons from ammonia, hydrogen gas, hydrogen sulfide, or certain minerals such as iron – Some are photosynthetic • Cyanobacteria- have chlorophyll – Other types split hydrogen sulfide instead of water to produce sulfur as a by-product Cyanobacteria 28.2 Bacteria and Archaea • Bacterial Diseases in Humans – Most bacteria are non-pathogenic – Disease-causing bacteria have genes that code for virulence factors • These genes can be transferred between bacteria 28.2 Bacteria and Archaea • Bacterial Diseases in Humans – Streptococcus Infections • Cause more disease than any other genus • Pharyngitis: most common and mild strep disease • Streptococcus pneumoniae: important agent in bacterial pneumonia • Streptococcus mutans: contributes to dental caries • Streptococcus pyogenes: causes the most diseases of any strep – Impetigo in infants: mild skin disease – Rheumatic fever: from endotoxins – Necrotizing fasciitis: “flesh-eating” bacteria Streptococcus pyogenes 28.2 Bacteria and Archaea • Bacterial Diseases – Tuberculosis • Highest mortality worldwide of any disease • 1/3 of the world’s population is infected • Caused by Mycobacterium tuberculosis • Active lesions in lung cause tubercles from immune response – Become calcified 28.2 Bacteria and Archaea • Bacterial Diseases in Humans – Food Poisoning • Bacteria cause food poisoning by two methods – They may cause an infection while growing in the intestines » Salmonella – They may produce a toxin while growing in food » Staphylococcus » Clostridium botulinum 28.2 Bacteria and Archaea • Bacterial Diseases in Humans – Chlamydia Infections • Chlamydia trachomatis – small intracellular parasite that causes a variety of diseases » Blindness » Pelvic inflammatory disease (an STD) 28.2 Bacteria and Archaea • Bacterial Diseases in Humans – Drug Control of Bacterial Diseases • Antibiotics – Inhibit protein synthesis by bacteria » Ex: Erythromycin and tetracyclins – Inhibit cell wall biosynthesis » Penicilins and cephalosporins • Problems related to antibiotic therapy – Potentially fatal allergic reactions – Killing off of normal flora – Bacterial resistance 28.2 Bacteria and Archaea • Biology of Archaea – Archaea are more closely related to Eukarya than bacteria • Based on nucleic acid similarities – Inhabit extreme environments • Extreme thermoacidophiles: live in habitats with high temperature and low pH • Methanogens: live in anaerobic environments • Halophiles: live in salty habitats 28.2 Bacteria and Archaea • Archaeal Structure – 0.1-15 microns in size – DNA genome is a single, closed circular molecule – Gram-positive archaea have thick polysaccharide cell wall – Gram-negative archaea have a protein surface layer – Cell membranes-single lipid layer which may be highly branched – Chemical characteristics make them acid and heat tolerant – Reproduce by binary fission 28.2 Bacteria and Archaea • Archaeal Metabolism – Some are heterotrophs, some are autotrophs – Halophiles have a unique photopigment resembling a pigment in human retina – Many are obligate anaerobes • Methanogens reduce carbon dioxide to methane – Found in swamps, lake sediments, hot springs, and digestive tracts of animals (especially cows) – Methane is a greenhouse gas Extreme Habitats 28.3 Protists • Domain Eukarya, Kingdom Protista – Generally microscopic and unicellular – Most reproduce asexually, but may reproduce sexually under adverse environmental conditions • Form spores or cysts to survive unfavorable conditions – Protists may be grouped according to mode of nutrition • Algae: Photosynthetic • Protozoans: Heterotrophic by ingestion • Water molds: Heterotrophic by absorption 28.3 Protists • Biology and Diversity of Algae – Can be unicellular, colonial, or filamentous – Size ranges from unicellular types about the size of bacteria to multicellular forms 100 feet long (“seaweeds”) – Algae carry out photosynthesis – Algae generally have a rigid cell wall 28.3 Protists • Green Algae – Closely related to plants as they have some similar characteristics • Cell walls contain cellulose • Have chlorophyll a and b • Store food as starch – Representatives of different types of Green Algae • • • • Chlamydomonas: unicellular green algae with two flagella Volvox: a colonial green algae Spirogyra: a filamentous green algae Ulva: a multicellular green algae Representative Green Algae 28.3 Protists • Diatoms – Most numerous unicellular algae in the oceans – Utilize a brown pigment in addition to chlorophyll • Base of many marine food chains – Component of phytoplankton – Intricate shells of silica 28.3 Protists • Dinoflagellates – Have cellulose plates and two flagella – Component of phytoplankton • Can produce neurotoxin• Responsible for “red tides” – Generally photosynthetic – Some have bioluminescence 28.3 Protists • Red Algae – Mainly multicellular seaweeds – Contain red and blue pigments as well as chlorophyll – Produce useful gelling agents • Agar • Carageenan 28.3 Protists • Brown Algae – Multicellular seaweeds, kelps – Has accessory pigments ranging in color from brown to black – Sargasso Sea-has large floating mats of brown algae – Harvested for food in some parts of the world • Also as a source of algingelatinous product used in foods 28.3 Protists • Euglenoids – Freshwater unicellular organisms – Most have chloroplasts but some do not – Have two flagella – Have a photoreceptor called an eyespot – Plasma membrane is surrounded by a flexible pellicle • Allows movement Euglena 28.3 Protists • Biology and Diversity of Protozoans – Usually motile eukaryotic unicellular heterotrophic protists – Commonly divided and classified by mechanism of locomotion – Wide distribution • Aquatic habitats (zooplankton) – Many are parasitic – Variable cell structure • Some have more than one nucleus • Contractile vacuoles- regulate water balance • Some produce cysts for survival in adverse conditions 28.3 Protists • The Ciliates – Largest group of protozoans – Move by means of cilia – Cilia aid in prey capture and feeding – Examples: Paramecium and Stentor • Amoeboids – Move by pseudopodia – Aquatic, freshwater and saltwater forms – Component of zooplankton – Feed by phagocytosis – Some cause disease Ciliates Amoeboids 28.3 Protists • Zooflagellates – Move by flagella – Most are symbiotic, many parasitic • Trypanosoma brucei– Causes African sleeping sickness – Tsetse fly is vector – Lives in bloodstream of host • Giardia lamblia– Causes giardiasis » Severe diarrhea 28.3 Protists • Sporozoans – Generally nonmotile with complex life cycles – Intercellular or intracellular parasites – Produce resistant spores – Malaria • Most widespread and dangerous sporozoan disease • Caused by Plasmodium vivax• Spread by mosquitoes 28.3 Protists 28.3 Protists • Toxoplasma gondii – – – – Causes Toxoplasmosis Oocysts commonly transmitted by infected cats For most people, it produces only mild flu-like symptoms In pregnant women it can infect the fetus and cause neurological damage • Cryptosporidium – Causes mild gastroenteritis in most, but can be fatal in people who are immunosuppressed – Passed in feces of infected animals – Can pass through water filtration processes and is unaffected by chlorination 28.3 Protists • Molds as Protists – Water Molds • Saprophytic, live off dead matter • Have a filamentous body with cell walls of cellulose • Produce flagellated spores during asexual reproduction • During sexual reproduction, produce eggs and sperm • Molds as Protists – Cellular Slime Molds • Exist as individual amoeboid cells • Common soil decomposers • When food is scarce, they aggregate together to form a pseudoplasmodium – This gives rise to sporangia which produces spores – Spores germinate releasing haploid amoeboid cells 28.3 Protists 28.4 Fungi • General Characteristics – True multicellularity (different types of cells) – Strict heterotrophs – Release enzymes into environment- digestion is extracellular – Most are saprophytic – Along with bacteria, fungi are important as decomposers 28.4 Fungi • Biology of Fungi – Body of fungus is a mass of filaments called a mycelium • Each filament is a hypha – Some have crosswalls between cells called septa » Septa have pores that allow fungal cells to exchange components of the cytoplasm – Nonseptate fungi lack crosswalls between cells-multinucleate – Fungal Cell Structure • Cell walls contain chitin instead of cellulose • Energy reserve is glycogen like in animal cells • Fungi are nonmotile • Move toward food source by growing toward it 28.4 Fungi • Biology of Fungi – Fungal Reproduction • Adapted to dry land • Produce wind-blown spores – Haploid reproductive cell germinates and develops into new mycelium (asexual) – Sexual reproduction occurs by the conjugation of two different mating types » Designated as + and – » After fusion of nuclei a zygote forms » The zygote undergoes meiosis » Produces haploid spores and cycle begins again 28.4 Fungi • Zygospore fungi (phylum Zygomycota) – Saprotrophs and parasites – Rhizopus stolonifer –black bread mold is a familiar zygospore fungus 28.4 Fungi • Sac Fungi (phylum Ascomycota) – Sexual reproductive structure called an ascocarp – Many sac fungi reproduce by producing chains of spores called conidia – Disease-causing sac fungi • Chestnut blight, Dutch elm disease, Ergot – Some sac fungi are useful to humans • Original source of penicillin • Used to produce blue cheese • Yeasts are used in the food industry Reproduction in Sac Fungi Sexual Asexual 28.4 Fungi • Club Fungi – Phylum Basidiomycota – Characteristic sexual reproductive structure is called a basidium • Contained within a basidiocarp – Edible part of a mushroom is the basidiocarp – Forms after fusion of + and – hyphae – Sexual reproduction is most prominent in this group • Asexual reproduction can occur by asexual spores Sexual Reproduction in Club Fungi 28.4 Fungi • Environmental Aspects of Fungi – Fungi and Photosynthesizers • Lichens – – – – – Associations between fungi and cyanobacteria or green algae Efficient at acquiring nutrients and moisture Can colonize poor soil, rocky surfaces Produce organic matter and create new soil Three characteristic forms- crustose (compact), foliose (shrublike), fruticose (leaflike) – Body of lichen has three layers-fungi form top and bottom layers and protect middle layer of photosynthetic cells » Fungi portion offers protection and delivers water » Photosynthesis gives the fungus nutrients Lichen Morphology 28.4 Fungi • Environmental Aspects of Fungi – Mycorrhizal Fungi • Mutualistic relationships with plant roots – Helps plants to grow more successfully in poor soils • Fungi can live on the outside surface of roots, or it can penetrate the root tissues – Plant provides organic nutrients to the fungus – Fungus brings water and minerals to the plant » Hyphae provide lots of surface area for water absorption 28.4 Fungi • Fungal Diseases of Plants – Many enter through the stomata of the leaves or through a wound – Smuts and rusts: sac fungi that parasitize cereal crops 28.4 Fungi • Fungal Disease of Humans (mycoses) – Tineas • Caused by moldlike fungi – Ex: Athlete’s foot • Ringworm – Redness and inflammation due to enzymes released by the fungus; extends outward in a ring-shape – Histoplasmosis (Histoplasmosis capsulatum) • Can be transmitted by bird droppings – May be asymptomatic of mild, flu-like symptoms – In more serious cases, lesions may form in the lungs which later become calcified – Candidiasis (Candida albicans) • Yeast infections resulting from imbalance of normal flora 28.5 Viruses, Viroids, and Prions 28.4 Fungi • Control of Fungi – Fungi more closely resemble animal cells than bacteria – Makes it harder to develop antibiotics that will kill fungi and not the host – Fungi synthesize steroids differently• Fungicides are directed at steroid biosynthesis 28.5 Viruses, Viroids, and Prions • Biology of Viruses – Viral Structure • Smaller than bacteria – Viruses are usually smaller than 0.2 microns – Bacteria are usually longer than 1 micron • Two main components to all viruses – Capsid (outer portion comprised of proteins) » May be surrounded by a lipid envelope » Spikes may be present for attachment to a host cell – Nucleic acid core (DNA or RNA) » Both DNA and RNA may be single or doublestranded, depending on the virus Viruses 28.5 Viruses, Viroids, and Prions • Viral Replication – Viruses are specific to a particular host • Spikes on a virus configure exactly to receptor molecules on the membrane of a potential host cell Life Cycle of an Animal Virus (RNA) 28.5 Viruses, Viroids, and Prions • Viral Replication – Latency • Viral genome of some viruses can lie dormant within host cell genome – Called a provirus – Viral DNA is replicated along with the host genome – Stress may stimulate provirus to enter biosynthesis stage • Retroviruses – Genome is in RNA – Enzyme reverse transcriptase transcribes RNA into DNA » This DNA is called cDNA (copy DNA) – cDNA can incorporate into host cell genome – Example: Human Immunodeficiency Virus (HIV) 28.5 Viruses, Viroids, and Prions • Viral Diseases in Humans – The Common Cold and Influenza • Colds are caused mainly by rhinoviruses – Runny nose, mild fever (possible), fatigue – Lasts around a week • Flu is caused by influenza viruses – High fever, chills, body aches, severe fatigue – Can be fatal – May last several weeks • Antigens on cold and flu viruses can change – Antigenic drift – Antigenic shift Antigenic Drift and Antigenic Shift 28.5 Viruses, Viroids, and Prions • Viral Diseases in Humans – Measles • Very contagious human disease • Spread by respiratory route • 7-12 day incubation period before flu-like symptoms and rash appear • Major killer worldwide in non-vaccinated populations • MMR vaccine protects against measles 28.5 Viruses, Viroids, and Prions • Viral Diseases in Humans – Herpesviruses • Remain latent much of the time • Four types of herpesviruses that cause disease in humans – Herpes simplex type 1: cold sores and fever blisters – Herpes simplex type 2: genital herpes – Herpes zoster: chickenpox and shingles – Epstein-Barr virus: infectious mononucleosis 28.5 Viruses, Viroids, and Prions • Viral Diseases in Humans – Antiviral Drugs • Antibiotics are most effective against viruses • Some antiviral drugs interfere with viral replication • Other antiviral drugs may affect virus attachment • Many times, no drugs are available for viral infections. 28.5 Viruses, Viroids, and Prions • Viroids and Prions – Acellular pathogens • Viroids are naked RNA molecules which do not code for proteins – Infect plant cells and cause disease • Prions are proteinaceous infectious particles – Normal protein change their shape, this causes other normal proteins to change their shape – Causes degenerative diseases of the nervous system – Prions are passed through ingestion of infected tissues » Scrapie in sheep » Mad cow disease in cattle » Creutzfeld-Jakob disease in humans » Kuru: human to human transmission through cannibalism