Chapter 26 - Bacteria and Archaea

In a microbial mat, where are the aerobic and anaerobic layers most likely to be found?

- Aerobic layers are most likely found in the surface - Anaerobic layers are most likely found in the interior of the mat

Anammox

- Anaerobic Ammonia Oxidation - ammonium ion is oxidized to nitrogen gas, and nitrite is reduced to nitrogen gas, with water produced as a by-product - provides only a small amount of energy, but it supports many bacteria and archaeons in oxygen-depleted parts of the ocean, providing a major route by which fixed nitrogen returns to the atmosphere as N2

How is nitrogen cycled through biological systems and why is this important to living organisms?

- Fixation is a process in the nitrogen cycle where bacteria turn nitrogen into ammonium. - After fixation, bacteria uses nitrification to turn ammonium into nitrates which is usable by plants. - Once nitrogen has been fixed, plants can absorb nitrogen through their roots from the soil in a process known as assimilation. - After a plant dies, it decomposes where bacteria turn the nitrogen back into ammonium through a process called ammonification. - During denitrification, special bacteria return extra nitrogen from the soil into the air. - They breakdown and recycle complex proteins and other materials. Without it, dead things would not decay and return to the Earth

What is the significance of nitrogen fixation and where does this process occur?

- Nitrogen fixation is the process of converting N2 into a biologically useful form such as ammonia - it takes place in the root nodules

What are the roles of nitrogen fixation and denitrification in moving nitrogen between the atmospheric and biological reservoirs?

- Nitrogen fixation is when bacteria turn nitrogen into ammonium because once the nitrogen is fixed plants can absorb the nitrogen through their roots from the soil - Denitrification is when bacteria convert nitrate into nitrogen gas and return it to the atmosphere

How are archaea similar and different from bacteria?

- SIMILARITIES: cells do not contain a nucleus and other membrane-bound organelles, DNA occurs in a circular form, same ribosome size, capable of nitrogen fixation, and capable of chemoautotrophy -DIFFERENCES: Archaea - membrane lipids ether-linked; Bacteria - membranes lipids ester-linked, Bacteria - photosynthesis with chlorophyll, Bacteria cell wall contains peptidoglycan

How is sulfur cycled through biological systems and why is this important to living organisms?

- The mineralization of organic sulfur to the inorganic form, hydrogen sulfide, H2S - Oxidation of sulfide and elemental sulfur (S) and related compounds to sulfate, SO42- - Reduction of sulfate to sulfide. - Microbial immobilization of the sulfur compounds and subsequent incorporation into the organic form of sulfur -Sulfur is released from geologic sources through the weathering of rocks. Once sulfur is exposed to the air, it combines with oxygen, and becomes sulfate SO4. Plants and microbes assimilate sulfate and convert it into organic forms. As animals consume plants, the sulfur is moved through the food chain and released when organisms die and decompose.

Cyanobacteria

- all bacteria capable of oxygenic photosynthesis

Periodic selection

- episodic loss of diversity - populations subject to the same episodes of periodic selection belong to a single species

Chemoautotrophs

- gain carbon by reducing CO2 to form carbohydrates but they obtain the energy to fuel this process from chemical reactions, not sunlight - use chemical reactions to generate ATP, but use inorganic molecules present in their local environment

Bacteriochlorophyll

- light-harvesting pigment closely related to the chlorophyll found in plants, algae, and cyanobacteria - used to absorb sunlight by anoxygenic photosynthetic bacteria

Horizontal gene transfer

- major source of genetic diversity in bacteria - obtaining new genes from distance relatives

Proteobacteria

- most diverse of all bacterial groups include many of the organisms that populate our expanded carbon cycle and other biogeochemical cycles

Hyperthermophiles

- organisms (archaeons) that require high temperature - mostly anaerobic - anaerobic, hyperthermophilic organisms near the base of the archaeal tree

Coevolution

- prokaryotes have coevolved with eukaryotes - evolved because they affected each other's evolution (in relation to the other)

Fermentation

- provides an alternative to cellular respiration as a way of extracting energy from organic molecules - partial oxidation of carbon compounds to molecules that are less oxidized than CO2 - does not require an external electron acceptor such as O2

What are the extreme lifestyles of the archaea that have evolved? How could natural selection have played a role in the evolution of these extreme abiotic tolerances?

- temperature preference, salt tolerance (halophilic), acid tolerance, and production of methane within the domain (methanogenic) - they filled niches that went unused

Gram-positive bacteria

- those that retain the dye - include organisms that cause and cure disease

Photoheterotrophs

- use energy from sunlight to make ATP, but rather than reducing CO2 to make their own organic molecules, they rely on organic molecules obtained from the environment - allows organisms to use all their absorbed light energy to make ATP while directing all absorbed organic molecules toward growth and reproduction

Nitrification

Ammonia is oxidized to nitrate (NO3-)

3 major divisions of Archaea

Crenarchaeota, Euryarchaeota, and Thaumarchaeota

Conjugation

DNA (usually a plasmid) form a donor cell is transferred through a pilus into the recipient cell

Transduction

DNA is transferred from a donor to a recipient cell by a virus

Transformation

DNA released into the environment by dead cells is taken up by a recipient cell

Denitrification

Use nitrate as an electron acceptor in respiration and return nitrogen to the atmosphere as nitrogen gas

Crenarchaeota and Euryarchaeota include

acid-loving microorganisms

Euryarchaeote archaeons include

heat-loving, methane-producing, and salt-loving microorganisms

Stromatolites

layered structures that record sediment accumulation by microbial communities

What are stromatolites?

layered structures that record sediment accumulation by microbial communities

Thaumarchaeota

may be the most abundant cells in the oceans

Assimilation

plants take up sulfate ions from the soil and reduce them within their cells to hydrogen sulfide

Nitrogen fixation

process of converting N2 into a biologically useful form such as ammonia

Primary producers

reduce CO2 to form carbohydrates

Plasmids

small circles of DNA that replicate independently of the cell's circular chromosome

Structural support of bacteria

structural support is provided by a cell wall made of peptidoglycan