28.1 The Microbial World

1. 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

2. Pasteur’s Experiments

3. 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

4. 28.2 Bacteria and Archaea

5. 28.1 The Microbial World • Typical Bacteria Cell • Bacteria can be categorized based on their cell wall • Gram positive • Gram negative

6. 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

7. Binary Fission

8. 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

9. Cyanobacteria

10. 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

11. 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

12. Streptococcus pyogenes

13. 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

14. 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

15. 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)

16. 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

17. 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

19. 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

20. 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

21. Extreme Habitats

22. 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

23. 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

24. 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

25. Representative Green Algae

26. 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

27. 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. 28.3 Protists • Red Algae • Mainly multicellular seaweeds • Contain red and blue pigments as well as chlorophyll • Produce useful gelling agents • Agar • Carageenan

29. 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 algin-gelatinous product used in foods

30. 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

31. Euglena

32. 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

33. 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 28.3 Protists

34. Ciliates

35. Amoeboids

36. 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

37. 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

38. 28.3 Protists

39. 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

40. 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

41. 28.3 Protists

42. 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

43. 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

44. 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

45. 28.4 Fungi • Zygospore fungi (phylum Zygomycota) • Saprotrophs and parasites • Rhizopus stolonifer –black bread mold is a familiar zygospore fungus

46. 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

47. Reproduction in Sac Fungi Sexual Asexual

48. 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

49. Sexual Reproduction in Club Fungi

50. 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