Chapter 27: Prokaryotes

Cutting Board (Eubacteria)

What are Prokaryotes?

Morphological Diversity See text for a better look at these, but no need to memorize these or associated information

Common Bacterial Shapes

Spirochete

Cyanobacteria (blue-green algae) Cyanobacteria are oxygen-liberating photosynthetic bacteria

A Prokaryotic Cell

Bacterial Cell Walls Thicker peptydoglycan layer but no outer membrane Thinner peptydoglycan layer and outer membrane Peptidoglycan is material making up bacterial cell wall

Bacterial Cell Walls “One of the most important features of nearly all prokaryotic cells is their cell wall which maintains cell shape, provides physical protection, and prevents the cell from bursting in a hypotonic environment.” p. 534, Campbell & Reece (2005) “In a hypertonic environment, most prokaryotes lose water and shrink away form their cell walls (plasmolyze), like other walled cells. Severe water loss inhibits the reproduction of prokaryotes, which explains why salt can be used to preserve certain foods, such as pork and fish.” pp , Campbell & Reece (2005)

Gram Stain Purple are Gram positive Pink are Gram negative

Bacterial Capsule Capsules provide desiccation resistance, attachment to surfaces, and resistance to phagocytosis

Bacterial Fimbriae Fibriae are involve in bacterial attachment to surfaces and resistance to phagocytosis

Conjugation Sex pili effect the transfer of conjugative plasmids

Bacterial Flagella Flagella effect motility Movement can be down or up concentration gradients, e.g., toward food

Flagella

Invaginated Plasma membranes Some prokaryotes display invaginated plasma membranes This increases membrane area, just as seen, e.g., in mitochondria

Endospores Some bacteria can form endospores, which are non- replicative cell forms that are highly resistant to environmental insult

Endospores

Biofilms Surface coating colonies of bacteria (often of more than one type) are called biofilms

Bacterial O 2 Requirements  Obligate aerobes require a functioning electron transport chain to grow, with O 2 as a typical final electron acceptor Key is their obligate use of an ETS to make ATP Also key is their ability grow in the presence of oxygen (O 2 )  Facultative anaerobes can use O 2 as a final electron acceptor for their electron transport chain (i.e., as aerobes), if available, but can grow using only fermentation (no ETS) if O 2 is not available.  Obligate anaerobes cannot grow in the presence of O 2 because they are poisoned by its presence Some obligate anaerobes are obligate fermenters Other obligate anaerobes are users of electron transport chains

Oxygen Requirements

Bacterial Nutrional Modes Know that outside parentheses

Nitrogen Metabolism  Together, bacterial species are very adept at metabolizing different forms of nitrogen, far more adept than are the sum of the eukaryotes  Nitrogen fixing is the conversion of atmospheric N (N 2 ) into bioavailable N (e.g., NH 3, ammonia)  Denitrification is the conversion of non- atmospheric N (nitrate and nitrite, NO 3 - and NO 2 - ) to N 2 (thus making the nitrogen no longer bioavailable except to nitrogen fixers)  The process by which denitrification occurs is known as anaerobic respiration, cellular respiration in which something other than O 2 is reduced as the final electron acceptor  "In terms of nutrition, nitrogen-fixing cyanobacteria are the most self-sufficient of all organisms. They require only light, CO 2, N 2, water, and some minerals to grow.” p. 539, Campbell & Reece (2005)

Specialized N 2 -Fixing Cells Nitrogen-fixing cyanobacteria

Archaea  Archaea are unusual in terms of the environments in which they live, the substrates they consume, and the products they release  Included among Archaea are various extremophiles: Extreme halophiles, organisms which live in extremely salty environments such as inland seas Extreme thermophiles, organisms which live in hot springs and deep-sea hydrothermal vents Mathanogens, which live in anaerobic environments, release methane as a metabolic waste product, thus producing marsh gas and flatulence from cellulose consuming herbivores (e.g., cattle, termites)  Archaea are also found in less extreme environments but those species of Archaea have not been studied as extensively as Archaea that live in extreme environments

Comparisons…

Symbiosies  Symbioses are intimate, relatively long-term interaction between organisms  Typically at least one of the organisms (the symbiont) benefits from the relationship  We can classify symbioses in terms of the degree to which the other organism (e.g., the host) benefits or is harmed: Commensalism: one organisms benefits while the other neither benefits nor is harmed Mutualism: both organisms benefit Parasitism: one organism is harmed by the symbiont (the parasite)  A number of bacterial species can enter into either Commensal, Mutual, or Parasitic relationships with eukaryotic organisms, such as animals

Example: Mutualism It is mutualistic bacteria that produce the glow in these fish

Toxins  Bacterial parasites typically have some means by which they can harm the host organism, such as by producing toxins  Toxins are chemical (often protein) agents that damage host tissue  Endotoxin is the Lipid A portion of LPS (not a protein) which causes host overreaction Endotoxin is produced by Gram-negative bacteria  Exotoxins are protein toxins, typically produced by Gram-positives as exoenzymes or equivalents But also many Gram-negatives Examples include Neurotoxins and Enterotoxins

Bacterial Diseases

The End