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Chapter 5 The Microbial World

Viruses Non-cellular infectious agents that have two basic characteristics: Not capable of reproduction without a host cell Structure: Nucleic acid core- can be DNA or RNA Capsid (Protein coat)- consists of numerous protein subunits organized into rod-like or many sided shape. Protein coat also contains specific proteins that bind with receptors on host cells (great at mimicry!!) Many glycoprotein spikes extend from coat-these spikes mutate so frequently that our immune system cannot keep up.

Viruses Notable Types of Viruses: Retroviruses- store genetic information in the form of nucleic acid known as RNA Lysogenic viruses – reproduce by inserting their DNA into the DNA of the host cell Bacteriophages – viruses that infect bacteria

Viruses Viruses in the Marine Community: They are common in marine waters They can infect bacteria, plankton, fish, sea turtles and marine mammals Lysis (bursting) of viral infected cells spills contents and releases large amounts of organic matter that can be utilized by other organisms (dissolved organic matter or DOM)

Prokaryotes Archaea and Bacteria Characteristics of Archaean and Bacterial Cells: Prokaryotic- no nucleus Single chromosome (normally circular)- some also with plasmids Most with cell wall Great metabolic diversity

Prokaryotes Archaea – “Ancient organisms” – fossils found that date back “3.8 billion years” Some live in very extreme environments Variety of metabolic types Widely distributed in the marine community They can tolerate wide ranges in temperature, salinity and even desiccation (drying out) Can be found in many areas including near hydrothermal vents and salt flats (two very extreme environments)

Prokaryotes Special Features of Bacteria: A variety of shapes including spirals, spheres, rods and rings Cell wall structure is semi-rigid, but permeable; most with cell wall Size is normally microscopic, but a few are large Wide variety of metabolic types Very abundant worldwide

Prokaryotes Special Features of Bacteria: One of the most important jobs of bacteria in the marine community is to break down dead organic matter – this forms detritus, which are minute particles of organic matter now available as nutrition for other organisms Cyanobacteria are a group of photosynthetic bacteria Stromalites, massive calcareous mounds formed by cyanobacteria, have been found that are billion years old

Prokaryotes Metabolic diversity: Photosynthesis – derive energy from light Chemosynthetic – derive energy from chemical compounds Heterotrophs – derive energy from organic matter by respiration

Diatoms Diatoms: Photosynthetic Yellow-brown color in life is a result of photosynthetic pigments, chlorophyll A and C and carotenoids Shell of silica called a frustule Most important primary producer on Earth Mostly solitary and unicellular Some can form colonies

Diatoms Diatoms Around half of the 12, 000 known species are marine Most are planktonic Store excess energy as an oil which also aids in buoyancy Tiny pores in shell used for gas/nutrient exchange Some produce a toxin, known as domoic acid, that can accumulate in the tissues or organisms that eat diatoms such as shellfish and small fish Larger organisms that eat these shellfish or small fish can become ill or die from this accumulated toxin

Diatoms Diatoms Mainly reproduce by cellular division (a form of asexual reproduction) In this type of reproduction, the cell divides and each result cell gets one-half of the frustule. This cell now must secrete the other half of the frustule (smaller piece) Due to this, diatoms get smaller each time they reproduce To restore normal size, they must either sexual reproduce or cast off the frustule and secrete an entire new frustule

Dinoflagellates Dinoflagellates Most species live in marine environment Mostly photosynthetic, some can ingest particles Each species has unique shape reinforced by plates of cellulose Two flagella in grooves on body that produce motion Also reproduce by cellular division Some are bioluminescent (read “Bay of Fire” on pg. 96)

Dinoflagellates Dinoflagellates Zooxanthellae are important dinoflagellates that live in a symbiotic relationship with corals, sea anemones and other organisms (many of these host organisms have little or no growth without their symbiotic partner)

Algal Blooms Diatoms and dinoflagellates can go through periods of rapid growth known as “blooms” This is a result of high levels of nutrients in the water These blooms can be harmful to marine organisms and even people at times

Protists Dinoflagellates A few species lack chloroplasts and live as parasites in marine organisms Some species can reproduce in larger numbers and produce “Red Tide” (read “Red Tides and Harmful Algal Blooms, pg. 338) Pfiesteria is a dinoflagellate that produces very serious toxins that can cause massive fish kills, harm shellfish and impair the nervous system in humans. Pfiesteria was discovered near the Outer Banks in North Carolina

Protists A few more species of phytosynthetic plankton: Silicoflagellates Star-shaped internal skeleton of silica Two flagella of varying lengths Coccolithophores Ornate shells of calcium carbonate

Protozoa Foraminiferans (forams) Exclusively found in marine community Found on sandy or rocky bottoms Shells of calcium carbonate Can be important contributors of calcareous material on coral reefs or sandy beaches Pseudopods (false feet) extend through pores in the shell where they are used to capture minute food particles such as phytoplankton

Protozoa Radiolarians Planktonic, mostly microscopic, although a few can reach large sizes Shell of silica Like forams, they use pseudopods that extend through pores in the shell where they are used to capture minute food particles such as phytoplankton

Protozoa Ciliates Cilia present for locomotion Most live as solitary cells Some build shells made of organic debris May live on hard substrate Some are planktonic

Fungi Eukaryotic and mostly multicellular Heterotrophic Most of the 1500 species of marine fungi are microscopic

Fungi Like bacteria, many fungus break down dead organic matter into detritus Some fungus live in symbiosis with cyanobacteria, these are known as lichens Marine lichens often live in wave-splashed areas of rocky shorelines and other hard substrate

Most Important Characteristics of Marine Microbes