PROKARYOTES (Domains: Bacteria and Archaea)

Prokaryotes  They are not Plants, included because: Tradition Comparative studies: e.g. photosynthesis Cause diseases to plants Provide insecticides (G.E.), antibiotics Present everywhere therefore influence plants (ecology)

Characteristics of Prokaryotes  The first organisms to inhabit earth (3.5 BYA)  Have nucleoid with a single circular DNA**  May have plasmid (accessory rings of DNA)  No histones (DNA is naked)

Structure of the Prokaryotic cell  Unicellular  Small cell µm  Some lack cell wall (pleomorphic) Cell wall gives bacteria its shape**  Lack cell organelles  Many bacteria (no cyanobacteria) have flagella

Prokaryotes: Reproduction  Asexual reproduction by binary fission (no mitosis)  Sexual reproduction does not occur but genetic material can be exchanged by:  Conjugation: transfer of genes between compatible individuals**  Transformation: incorporation and replication of DNA pieces from dead or alive prokaryotes  Transduction: incorporation of DNA pieces by means of bacteriophage  Prokaryotes mutate faster than eukaryotes. Why?

Conjugation in Bacteria dahlem.mpg.de/~ag_lanka/Bacterial_Conjugation.html

Prokaryotes: Nutrition Autotrophic prokaryotes  Produce their own food  1- Photoautrophs: use sun E. to reduce CO 2 into sugar Green sulfur bacteria: CO 2 + 2H 2 S  sugar + 2S Cyanobacteria: CO 2 + H 2 O  sugar + O 2 Important as primary producers

 2- Chemoautotrophs: aerobic, oxidize inorganic compounds e.g., NH 4 to obtain energy : Nitrifying bacteria: NH 4  NO 2  NO 3 The first step carried by Nitrosococcus & Nitrosomonas The second step by Nitrobacter important in N 2 cycle Prokaryotes: Nutrition Autotrophic prokaryotes

 Cannot make their food Chemoheterotrophs: aerobic, decomposers Symbiotic chemoheterotrophs: live in association with other living organisms as in Rhizobium/legume’s root association Rhizobium: fix atmospheric nitrogen into ammonia** Roots provide carbohydrates to Rhizobium Prokaryotes: Nutrition Heterotrophic prokaryotes

Rhizobium possesses the enzyme nitrogenase that breaks down atmospheric (N 2 ) into a form usable by plants (NH 4 )

The Need for O 2  Anaerobes: Obligate anaerobes: cannot grow in the presence of O 2 Facultative anaerobes: grow in the presence or absence of O 2 (most bacteria)  Aerobes: require oxygen

Classification of Prokaryotes  Bacteria have very little anatomy and virtually no morphology  Traditional classified on Metabolism (nutrition) Wall chemistry Ability to carry photosynthesis Sensitivity to O2 Presence of endospores  For many years Prokaryotes are classified as one Kingdom, Monera, with 2 divisions: Bacteria and Cyanobacteria

Recent Classifications  Recent classifications based on Ribosomal RNA  This type of classification reflects phylogenetic relationships  rRNA is chosen because of its involvement in protein synthesis and  Changes in rRNA sequence occur slowly over time

Recent Classifications

Domain Bacteria  Bacteria: the most common type of Prokaryotes

Cyanobacteria  Photosynthetic Cyanobacteria :  Cyanobacteria have phycobilin & Chl(a), lack chl(b)  Have photosystem I & II, liberate oxygen**  Live in a variety of habitats including Antarctica  Very old, enrich environment with O 2 (Stromatolites)**  Marine Cyanobacteria form Planktons

Examples of Cyanobacteria Cyanobacteria: primary producers in freshwater, soil, & moist habitats Early organisms that introduced O 2 into our atmosphere

Stromatolites Stromatolites (2.7BYA) Cyanobacteria’s mucus bind sand & CaCo 3

Nitrogen Fixing Cyanobacteria  Nitrogen fixation occurs within the heterocyst**  The heterocyst contains nitrogenase enzyme that breaks N 3 into ammonia

Heterocyst Cyanobacteria such as Nostoc & Anabaena possess a heterocyst where nitrogen fixation takes place

Purple & Green Bacteria  These are Photosynthetic, anaerobic Do not have Chlorophyll have baceriochlorophyll, carotenoid PS1 present, PSII lacking Electron flow is cyclic, (no O2, no ADPH+H) Use S (instead of water) to reduce CO2 CO2 + 2H2S (Light) = (CH2O)n + H2O + 2S

Prochlorophytes  Possess Chl a, b, & carotenoid, lack phycobilin  When Prochloron was discovered, it arose tremendous interest because:  Resembles chloroplasts  Exist as obligate symbiont inside marine invertebrates

Other Important Bacteria  Nitrogen fixing bacteria Free-living bacteria (Azotobacter, Derxia) Nitrifying bacteria Denitrifying bacteria Symbiotic ( Rhizobium, Agrobacteria)

Domain Archaea  Differ from bacteria in  Their base sequences of mRNA  Cell wall lack muramic acid  Their membranes have unusual lipid, not affected by drugs that inhibit ribosomes and protein synthesis  Their metabolism is exotic, thrive in unusual habitats  Evolutionary origin?  Evolved from bacteria (their unusual habitat acts as a selective pressure)  Their origin is ancient (began when earth is quite different: reduced atmosphere, acid pools, hot volcanic habitats)

Archaea & Eukarya  Archaea and Eukarya share: The same ribosomal proteins have histone proteins associated with their DNA as we do Initiate transcription in the same manner Have similar types of tRNA Therefore Eukarya are more closely related to Archaea than Bacteria

Types of Archaea  Most Archaea are chemoautotrophs.  Highly adapted to live in unusual habitats  Methanogens: Live in anaerobic habitats: swamps & marches -The only organisms capable of metabolizing CH 4 from H 2 & CO 2.  Halophiles: Require high salt for growth. –Common in areas such as the great salt lake and dead sea.  Thermoacidophiles: Live in acidic hot environment e.g., hot springs & around volcanoes. –Their plasma membrane contain unusual lipid that allow them to function at high temperature –They reduce sulfide into acidic sulfate