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Chapter 26 Environmental Microbiology 26.1 Water Pollution • Unpolluted and Polluted Water Contain Different Microbial Populations • Unpolluted water contains low organic nutrients, thus low numbers of microbes • Water can be polluted with • sewage • agricultural runoff • industrial pollutants • Polluted water is high in • organic matter • coliform and noncoliform bacteria • Accumulated phosphates cause algal blooms • The blooms supply nutrients to other microbes, which use up oxygen • Aquatic animals and plants die • They accumulate on the bottom where anaerobic bacteria thrive • Halophiles, psychrophiles, and barophiles thrive in the ocean • Diatoms and dinoflagellates are integral parts of food chains in the ocean • Most marine microorganisms live in the littoral zone • Some can live in the deep benthic and abyssal zones • There Are Three Types of Water Pollution • Physical pollution occurs when sand and soil or cyanobacterial blooms cloud the water • Chemical pollution occurs when inorganic and organic waste enter the water • Biological pollution occurs when microorganisms enter the water from anthropogenic sources • The biological oxygen demand (BOD) of water is the amount of water microbes need to decompose organic matter • Diseases Can Be Transmitted by Water • Diseases spread by contaminated water consumption include • typhoid fever • cholera • shigellosis • Legionnaires’ disease • • • • Erysipeloid is an infection caused by the marine pathogen Erysipelothrix rhusiopathiae Mycobacterium marinum can cause a lesion (granuloma) at the site of a wound Vibrio vulnificus can cause • intestinal illness if consumed • wound infections involving gangrene and necrotizing fasciitis Water can also transmit • Viruses such as • hepatitis A • rotavirus • gastroenteritis • polio virus • Eukaryotic microorganisms like • Entamoeba histolytica • Giardia lamblia • Crytosporidium • Toxin-producing dinoflagellates, which cause ciguatera poisoning in humans • For example, Gambierdiscus toxicus 26.2 The Treatment of Water and Sewage • Water Purification Is a Three-Step Process • Sedimentation removes large objects and particles through flocculation • Filtration removes microorganisms by passing water through a layer of • sand • gravel • accumulated microbe biofilm • Chlorination involves adding chlorine gas to kill remaining organisms • Sewage Treatment Can Be a Multistep Process • Domestic human waste usually empties into a cesspool or septic tank • Sewage (and livestock waste) can be collected in oxidation lagoons • Natural digestion occurs • Sewage treatment plants can treat large amounts of domestic wastewater • Biofilms Are Prevalent in the Environment • A biofilm is an immobilized population of microbes tangled together in fibers adhering to a surface • Microbes in a biofilm work together for • nutrient storage production • predator protection • Biofilms are used in bioremediation to degrade toxic wastes • Biofilms can form in the human body and on medical instruments • The Bacteriological Analysis of Water Tests for Indicator Organisms • Presence of indicator organisms shows that water has been contaminated by feces • Coliform bacteria live in mammalian intestines but can survive in water • The membrane filter technique and standard plate count are used to determine numbers of bacteria in a water sample • The most probable number test determines number of bacteria by observing carbon dioxide gas production 26.3 The Cycles of Elements in the Environment • The Carbon Cycle Is Influenced by Microorganisms • The Sulfur Cycle Recycles Sulfate Molecules • Microbes break down proteins and amino acids to yield compounds like hydrogen sulfide • • • Several bacterial genera transform hydrogen sulfide to sulfate • Plants use the sulfate in amino acids The Nitrogen Cycle Is Dependent on Microorganisms Nitrogen-fixing microbes live symbiotically with legume roots • They provide the plant and surrounding soil with usable nitrogen