The Microbial WorldChapter 5

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

• Two Domains: 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

–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)

Methanocaldococcus

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

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

Cyanobacteria

Stromalites

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

• 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

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

“Red tide”

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” –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