Eukaryotic Viruses & Microbial Pathogens PDF

Eukaryotic viruses  Microbial pathogens =microbes that cause disease 1,407 currently recognized species of pathogens affecting humans 538 bacteria 317 fungi 287 helminths (parasitic worms)...

Eukaryotic viruses  Microbial pathogens =microbes that cause disease 1,407 currently recognized species of pathogens affecting humans 538 bacteria 317 fungi 287 helminths (parasitic worms) 208 viruses 57 protists Woolhouse (2006)  Deaths due to infectious diseases in the world Disease Deaths Pathogens Acute respiratory infections 4,259,000 Bacteria, viruses, fungi AIDS 2,040,000 Virus Diarrheal diseases 2,163,000 Bacteria, viruses, protists Tuberculosis 1,464,000 Bacterium Malaria 889,000 Protist Measles 424,000 Virus Other 2,561,000 Bacteria, viruses, protists, fungi WHO (2004)  Human diseases caused by viruses Coronavirus RNA viruses make up the majority of emerging diseases Zika Hepatitis C Schaechter et al. (2006)  Recent outbreaks of infectious diseases (2008-2010) Cholera 2008 Plague 2009 H1N1 Polio Avian influenza 2009 Avian influenza Meningococcal 2009 2008 2009 disease 2009 Rift Valley fever 2007 Polio 2009 Yellow fever Ebola-like Avian virus 2009 Viral infection Yellow fever 2010 2008 influenza Ebola 2008 2009 Avian Dengue fever Cholera influenza 2008 2009 2009 Bacterial infection Yellow fever Rift Valley 2008 fever 2008 Since then: Cholera in Haiti (2010) Ebola in West Africa (2014) Zika in Brazil (2015) Coronavirus (2020)-pandemic (everywhere)  Epidemiology = study of disease in populations (i.e., occurrence, distribution and control) Endemic = disease is constantly present (usually in relatively low numbers), e.g., Malaria Epidemic = occurrence of a disease in unusually high numbers in a localized population, e.g., Cholera in Haiti (2010) or Ebola in West Africa (2014) Pandemic = a worldwide epidemic e.g., Flu pandemic (1918 or 2009), Covid-19 (2020)  Ebola epidemic (2014-2015) Ebola Electron microscope Basler (2014) Cell Host & Microbe  2009 Influenza pandemic Influenza Electron microscope Figure 33.21 Outbreaks and deaths due to infectious diseases in the USA 20th century 19th century COVID-19 deaths in the USA Smallpox hospital  The eradication of smallpox Smallpox is caused by the dsDNA virus Variola It was the most devastating of all infectious diseases Highly contagious Causes severe skin lesions Invades internal organs Science photo library Smallpox epidemics in Palestine (1922) 1st infectious disease for which a vaccine became available 1900-1979 – 300-500 million deaths Late 1940s, heat-stable, freeze-dried vaccine (developed by Collier) 1967 – 2 million dead/ WHO eradication program starts 1979 – declared eradicated by WHO Strains are still conserved in two laboratories in the USA and Russia  The discovery of viruses: TMV Tobacco Mosaic Virus (TMV) 1886 1890 1898 Adolf Mayer Dmitri Ivanovski Martinus Beijerinck (1843-1942) (1864-1920) (1851-1931) “Then I suddenly made the discovery Showed that the filtrate Coined the term “virus” that the juice from diseased plants remains infectious obtained by grinding was a certain “something infectious substance for healthy plants” Could be a toxin smaller than a bacterium”  Beijerinck’s experiment Juice of infected Healthy Infected tobacco leaves Filter Filtrate free of bacteria Disease develops. Virus reproduces and invades other cells (a toxin would be unable to reproduce)  TMV isolation (1935) Wendell Stanley (1904-1971) Nobel Prize 1946 Science 81:644-5 Ultrastructure of TMV: a nucleoprotein particle EM: Electron micrograph RNA Protein capsid (2,130 copies) Size: 18 x 250 nm  General characteristics of viruses Protein coated fragments of DNA or RNA (i.e. virion is a nucleoprotein particle) Obligate intracellular parasites (reproduce only within a host cell) Disassemble during reproductive cycle  Structure of viruses Viruses are not cells Virion = extracellular form of the virus Nucleic acid genome (DNA or RNA) Applies to all viruses Capsid (protein coat) Envelope (membrane) Not every virus Example: Ebola virus RNA genome Capsid Envelope  Capsid =protein shell that encloses the viral genome Various shapes (but always symmetric) Rod-shaped=helical symmetry, e.g. TMV, influenza Spherical=icosahedral symmetry, e.g. adenovirus, HPV, T4 bacteriophage Composition Single type of protein (e.g. TMV) Several types of protein (but less complex than bacterial spore coat)  Structure of viruses Adenovirus HIV TMV Rabies Schaechter et al (2006)  Host range =number of hosts that a virus can infect Narrow (only one host): Measles (humans), HIV (humans), SIV (simians) Broad (several hosts): Influenza (birds, mammals) West Nile Virus (insects, birds, mammals) Rabies (warm-blooded animals) Coronavirus (?, other mammals)  Size range for eukaryotic viruses Smallest virion is 17 nm in diameter = Porcine circovirus (ssRNA virus) 1,768 nucleotides 2 ORFs (replicase and capsid) Largest virion is ~1 m in length = Pandoravirus (dsDNA virus) 2.5 Mb >2,500 proteins? New Scientist (2013)  Viral reproductive cycle Viral proteins are synthesized by the host cell Host enzymes, ribosomes, tRNAs, amino acids, ATP, and other molecules are co-opted Spontaneous self-assembly into new viral particles Hi-jacking of the host cell  Baltimore classification of viruses DNA viruses RNA viruses David Baltimore (1938-) Baltimore (1971) Viral reproductive cycle for dsDNA-class I virus VIRUS (e.g. Adenovirus) Entry HOST CELL Viral DNA mRNA Expression Viral DNA of viral proteins Viral DNA Capsid Replication proteins Self-assembly Exit  Viral genomes (DNA or RNA) DNA viruses RNA viruses Nonenveloped Enveloped Nonenveloped Enveloped (all are ssRNA) Partially dsDNA TMV Rabies ssDNA ssRNA Influenza dsDNA ssRNA dsDNA Adenovirus Coronavirus dsDNA HPV dsRNA dsDNA Mimivirus dsDNA dsDNA HIV dsDNA Virus mutation rates Swiss Institute for Bioinformatics First genome sequences: bacteriophages 1976 1977 Phage MS2 Phage Φ-X174 (27 nm in diameter) (31 nm in diameter) (+) ssRNA virus (class IV) (+) ssDNA virus (class II) 3,569 nucleotides 5,386 nucleotides 4 proteins 11 proteins  Genome sizes: eukaryotic viruses Smallest viral genomes contain 2-4 genes: RSV (Rous Sarcoma Virus) 4 genes Oncogenic=causes tumors Property discovered in 1911 by Peyton Rous (Nobel Prize 1966, he was 87 years old!) Largest viral genomes, about a thousand genes (larger than some bacteria): Mimivirus (mimicking microbe): ~900 genes Megavirus: 1,100 genes Pandoravirus: 2,500 genes Mimivirus is one of the largest virus Genome size: 1.2 Mb, 911 proteins Acanthamoeba polyphaga (host) Mimivirus fiber layer protein capsid 10 m Total diameter 750 nm (capsid 400 nm) Larger than Mycoplasma Electron microscope  Structure of viruses Adenovirus HIV TMV Rabies Schaechter et al (2006)  Icosahedral viruses dsDNA-class I virus DNA Capsid 5-3-2 Symmetry 5-Fold 3-Fold 2-Fold Glycoprotein Human papilloma virus (HPV) (can cause cervical cancer) Gardasil vaccine (contains the major capsid protein of HPV) 70–90 nm 50 nm (diameter) Adenovirus  Membranous envelopes Only in some viruses (e.g., Ebola, Influenza, HIV, Rabies) Surrounds the capsid derived from the host cell’s membrane (=combination of viral and host cell proteins) 1) way to remain undetected 2) facilitates fusion (advantageous for spreading) Assembly of enveloped viruses Schaechter et al (2006)  Influenza is an enveloped virus ssRNA(-) class V virus Orthomyxovirus group Membranous envelope RNA (8 segments) 11 proteins Capsid (helical) Envelope proteins All other infectious diseases Colds Influenza 100 200 300 400 0 Cases per 100 people per year 80–200 nm 50 nm (diameter) Influenza virus  The 1918 flu pandemic (Spanish flu, H1N1) 20-100 million people worldwide died of the disease (about 3% of the world's population at the time, more casualties than World War I) Fort Riley, Kansas  H and N proteins of the viral envelope There are several types of H and N proteins e.g. H1N1 subtype (Spanish flu 1918, Swine flu 2009) H2N2 (Asian flu 1957) Neuraminidase (NA) Hemagglutinin (HA) HA trimer Lipid bilayer NA tetramer CDC Figure 33.21 Segmented RNA genome of the flu virus (class V) Influenza outbreaks occur annually due to genome plasticity 8 RNA segments Two factors Mutation=antigenic drift caused by replication errors Reassortment=antigenic shift Shuffling of RNA segments Eisfeld et al (2015)  Example of reassortment Bird Reassortant Human virus virus virus Infection with Infection human virus with bird virus Infection with Reassortment reassortant of human and virus bird virus © 2012 Pearson Education, Inc. Figure 33.22  Vaccines vs. drugs vs. antibiotics Antiviral drugs treat viral infections Antibiotics are natural compounds that only work against bacteria (not against viruses) Vaccines can prevent certain viral and bacterial infections Vaccines are harmless derivatives of pathogens that stimulate the immune system  Edward Jenner and the smallpox vaccine Vaccination: from the Latin Vacca=cow Noted that milkmaids usually do not get smallpox They are immune to the disease because they previously contracted cowpox (a similar but less severe infection) 1796, inoculates material recovered from cowpox blisters to a young boy Later injected fully virulent variolous material, but no infection developed The modern vaccine used a different virus, vaccinia Edward Jenner (1749-1823)  Louis Pasteur (1822-1895) 1849 Chirality (basis of stereochemistry) 1857 Alcoholic fermentation 1861 Disproving spontaneous generation 1864 Pasteurization 1875-1885 Immunization method 1881 Anthrax vaccine (on sheep) 1885 First patient cured of rabies by vaccination 1888 Inauguration of the Pasteur Institute Portrait by Albert Edelfelt (1886), Musée d’Orsay Rabies virus is a rhabdovirus (ssRNA (-), class V) Infects central nervous system of warm-blooded animals Proliferates in the brain and leads to fever, excitation, dilation of the pupils, excessive salivation, anxiety, and fear of swallowing Electron micrograph of rabies virus Bullet shape (-) ssRNA CDC Reservoirs in the U.S. are raccoons, skunks, coyotes, foxes, and bats Enters the body through a wound or bite Leads to death if not treated Preparation of the vaccine: attenuation The inoculation in the rabbit (…) of spinal cord of a dog suffering from common street rabies, always elicits rabies in these animals. If taking the greatest care possible to maintain purity one removes from these cords sections a few centimeters in length, and then suspends them in dry air, virulence slowly disappears. In a series of flasks in which air is maintained in a dry state (…), each day one suspends a thickness of fresh rabid spinal tissue taken from a rabbit dead of rabies. Each day as well, one inoculates under the skin of a dog (…) a small fragment of one of these desiccated spinal pieces, beginning with a piece most distant in time from when it was worked upon, in order to be quite certain that it isn’t at all virulent. By the application of this method, I had made fifty dogs of all ages and breeds refractory to rabies without a single failure. Louis Pasteur (1885); Report to the French Academy of Sciences  The story of Joseph Meister “Joseph Meister, 9 years old, also bitten on 4 July at 8 in the morning by the same dog. This child knocked to the ground by the dog carried numerous bites on the hand, legs, thighs, some rather deep that made his walking difficult… As the death of this child appeared inevitable, I Science photo library decided, not without deep and severe unease, as one can well imagine, to try on Joseph Meister the procedure which had consistently worked in dogs… Joseph Meister has thus escaped, not only from rabies that his bites would have produced, but also from that which I had inoculated him with in order to check his immunity produced by the treatment” Louis Pasteur (1885); Report to the French Academy of Sciences Nature Poliovirus is a picornavirus (ssRNA (+), class IV) (+) ssRNA virus pico- means small, 30 nm in diameter 7,500 nucleotides Synthesis of (+) strand Synthesis of (-) strand Poliovirus RNA genome VPg Translation Viral RNA is translated directly, Polyprotein polyprotein undergoes self-cleavage to generate smaller proteins Proteases Structural coat cleave polyprotein proteins Replicase (RNA-dependent RNA pol) Proteases Poliomyelitis is caused by poliovirus Enterovirus = acquired via fecal-oral route Destruction of motor neurons causing paralysis 1 in 200 infections leads to irreversible paralysis (WHO) 37 reported cases in 2016 (WHO)  Polio vaccines Two types: IPV (inactivated poliovirus)-injection-Salk (1952) OPV (attenuated poliovirus)-oral-Sabin (1957) Jonas Salk Albert Sabin (1914-1995) (1906-1993) Both trained at NYU Medical School Neither patented their vaccine  Strategies to develop a vaccine-summary Method#1: Identify a closely related virus (with similar antigens) that causes a mild disease (or no disease) (e.g., vaccinia vs. smallpox) Method#2: Attenuate or inactivate the virus to ensure that it will no longer cause the disease but antigens are not affected (e.g., rabies or polio or yellow fever vaccine) Method#3: Recombinant vaccine. Engineer microbes to express surface proteins from the virus. Purify these proteins (antigens) and use as vaccine. (e.g., Gardasil)  Retroviruses (ssRNA (+), class VI) =a class of RNA viruses that use reverse transcription to copy their RNA genome into DNA Howard David Nobel Prize in Physiology or Medicine Temin Baltimore 1975 (1934-1994) (1938-) Central dogma of molecular biology Gene expression DNA RNA Protein Reverse transcription Francis Crick  Human Immunodeficiency Virus (HIV) HIV is the retrovirus that causes AIDS (acquired immunodeficiency syndrome) Electron micrograph of HIV AIDS was recognized as a disease in 1981  HIV structure Viral envelope Viral enzymes: (lipid membrane bilayer) reverse transcriptase Glycoprotein integrase protease RNA (two identical strands) Capsid  Typical organization of a retrovirus genome (class VI) Cap gag pol env Processing GAG of GAG GAG - POL Processing of GAG-POL POL Capsid proteins Protease Reverse Integrase transcriptase Cap env Deleted ENV region Envelope proteins Figure 21.20 EP1 EP2  HIV entry HIV infects cells that contain the CD4 cell surface protein (T-helper cells) HIV gp120 binds CD4 and CCR5 Fusion of the HIV envelope with the host cell gp120 gp 120 CD4 CD4 CCR5 CCR5 T-helper Target cellcell © 2012 Pearson Education, Inc. HIV reproductive cycle Reverse HIV transcriptase Viral RNA Reverse RNA-DNA hybrid transcription DNA Provirus (integrated viral DNA) HOST CELL NUCLEUS  Progress of untreated HIV infection Symptom- Swollen lymph glands Subclinical immune Oppor- Systemic free dysfunction tunistic immune 1000 infections deficiency HIV 900 106 RNA copies Normal 800 per range ml for T cells 700 CD4 T cells 600 104 per 500 mm3 of Significantly blood 400 depressed T cells 300 Death 102 200 Severe T cell 100 depletion 0 0 6 12 18 24 30 36 42 48 54 60 66 72 78 84 Time (months) after HIV exposure © 2012 Pearson Education, Inc. AIDS statistics (USA and industrialized nations) There is not an effective vaccine for HIV Fauci et al (2005)  HAART: Highly Active AntiRetroviral Therapy Four classes of drugs delay the symptoms of AIDS and prolong the life of those infected with HIV Nucleoside reverse transcriptase inhibitors Thymine (e.g., AZT) Azidothymidine (AZT) Nonnucleoside reverse transcriptase inhibitors (e.g., Nevirapine) Nevirapine Peptide bonds Protease inhibitors (e.g., saquinavir) Saquinavir Fusion inhibitors (e.g., CCR5 antagonists) Combination of drugs to avoid evolution of resistance  AZT is a nucleoside analog AZT Thymidine (azidothymidine) azido group  Mode of action of AZT Termination of RNA dependent DNA polymerization Article#5: Bacteriophages and CRISPR Phage ΦKZ resists CRISPR–Cas and Restriction/Modification systems  Article#5: Bacteriophages and CRISPR Builds a proteinaceous nucleus-like compartment Replication of phage DNA takes place in compartment Protein barrier occludes immune enzymes A phage-encoded homologue of tubulin, PhuZ, centers the compartment within the host cell Chaikeeratisak et al (2017)  Article#5: Bacteriophages and CRISPR EcoRI and Cas9 cleave the phage DNA in vitro Fused EcoRI to phage-encoded protein internalized within the shell. EcoRI (E111G) is inactive Protists  What are protists? A diverse group of eukaryotic microbes Little in common Several are parasites and responsible for serious human diseases Schaechter et al. (2006)  Parasites Parasite = organism in a symbiotic association that benefits at the expense of the host Reduction of host fitness: modification of behavior, lower fecundity Parasitology = study of parasites, commonly applies to parasitic eukaryotes (even though many bacteria and every virus are also parasites)  Symbiosis =Greek for “living (bio-) together (syn-)” Ecological relationship between organisms of different species Host larger organism Symbiont smaller organism Endosymbiont=cell that lives within a host cell Mutualism both benefit Commensalism one organism benefits, the other is unaffected Parasitism Parasite (smaller organism) benefits at the expense of the host  Ernst Haeckel (1834-1919) Introduced the terms protist and phylogeny Protists represent the “kingdom of primitive forms” Kunstformen der Natur (1899) Art Forms in Nature  Haeckel’s tree of life Plants Protists Animals Generelle Morphologie der Organismen (1866) General Morphology of Organisms  What are protists? Eukaryotes that are neither fungi, plants nor animals Mostly unicellular (except some colonial and multicellular species) Mostly microscopic (except several types of algae, e.g., seaweed) Aquatic (freshwater, marine, bloodstream) Stentor (ciliate) D. sanguinea (red alga) unicellular multicellular Nutritionally diverse microscopic macroscopic (photosynthetic, heterotrophs, mixotrophs) freshwater marine chemoheterotroph photoautotroph  Nutritional diversity Algae photosynthetic = plant-like protists, photoautotrophs Protozoa ingestive = animal-like protists, chemoheterotrophs Mixotrophs organisms that are photoautotrophs and chemoheterotrophs (most are facultative mixotrophs, i.e., one mode is usually favored)  Phylogeny of Eukaryotes Diplomonads Excavata Parabasalids Euglenozoans Stramenopiles Alveolates Rhizarians Diatoms Protists are spread throughout Golden algae Brown algae the eukaryotic tree of life “SAR” clade Dinoflagellates Apicomplexans Ciliates Forams Four supergroups: Cercozoans Excavates Radiolarians SAR clade Archaeplastida Archaeplastida Red algae Chlorophytes Green Unikonta algae Charophytes Land plants Amoebozoans Opisthokonts Slime molds Tubulinids Unikonta Entamoebas Nucleariids Fungi Choanoflagellates Animals  Protist genomes sequencing projects Size Year 104 Mb 2006 72 Mb 2006 23 Mb 2002 120 Mb 2007 11.7 Mb 2007 160 Mb 2007 35 Mb 2005 Eisen et al. 2006  Genome sequences of parasites Trypanosoma brucei, T. cruzi, T. vivax, Leishmania, Crithidia fasciculata Giardia lamblia Trichomonas vaginalis Plasmodium, Cryptosporidium, Toxoplasma gondii, Babesia, Theileria, Eimeria tenella, Neospora caninum  Genomes sequences of vectors Aedes aegypti, Anopheles gambiae, Culex pipiens, Ixodes, tsetse, body louse, kissing bug Vector=an organism (usually an arthropod) that transmits the parasite to the host Diseases caused by Excavates Giardiasis Excavata Diplomonads Parabasalids Trichomoniasis Euglenozoans Trypanosomiasis Giardiasis  Giardia, a diplomonad Giardia intestinalis Giardiasis results from drinking water contaminated with Giardia cysts No mitochondria, but possible vestigial mitochondrion= mitosome Two transcriptionally active diploid nuclei 5 µm  Giardia lamblia genome 12 Mb; 5 chromosomes; 6,500 genes Simplified forms of many cellular processes Favors model of early divergence from other eukaryotes, rather than genome reduction Morrison et al. (2007) Trichomoniasis Trichomonas vaginalis, a parabasalid Flagella Undulating membrane 5 µm Trichomoniasis is a sexually transmitted human infection ~170 million cases annually  Annual incidence of STI in the USA HIV 40,000 Syphilis 70,000 Hepatitis B 77,000 Gonorrhea 650,000 Genital herpes 1 million Chlamydia 3 million Trichomoniasis Trichomoniasis 5 million HPV 5.5 million Total annual incidence 15 million Kaiser Family Foundation and American Social Health Association (1998)  Parasite structure Anterior flagella (4) Recurrent flagellum /undulating membrane Hydrogenosomes carbohydrate metabolism Axostyle Parabasal body (microtubules) /Golgi complex supportive structure or participates in cell division  Hydrogenosomes Anaerobic, No citric acid cycle Double membrane Common origin with mitochondria? Trichomonas vaginalis genome ~160 Mb, ~60,000 genes Much larger than expected! G+C content (33%) Trypanosomiasis Excavates Excavata Diplomonads Parabasalids Euglenozoans Trypanosoma  Euglenozoans Excavata Euglenozoans Flagella of euglenozoa contain a crystalline rod alongside a microtubules ring Flagella 0.2 µm Crystalline rod Ring of microtubules Electron microscope  Differences between eukaryotic and prokaryotic flagella Eukaryotic Prokaryotic Propeller Ring of microtubules (made of tubulin) Whip Flagellin 9 + 2 microtubule axoneme Diseases caused by kinetoplastids Trypanosoma brucei causes sleeping sickness (aka HAT: Human African Trypanosomiasis) Trypanosoma cruzi causes Chagas disease (aka American Trypanosomiasis) Leishmania major causes leishmaniasis  Kinetoplastids are Euglenozoans Light microscope + DAPI stain Kinetoplast=large mitochondrion that contains an organized mass of DNA Flagellum Kinetoplast (K) Nucleus (N) Electron microscope microtubules & crystalline rod  Human African Trypanosomiasis 70 million people are estimated to be at risk in Africa (2000-2009) 3,500 deaths in 2015 (used to be 10x more in 1990) Trypanosoma brucei T. b. gambiense Tsetse fly (Glossina) Simmaro et al (2012)  Discovery of the infectious agent (1894): Trypanosoma nagana disease in cattle, Ubombo village in Natal, South Africa (1894) Sketches of hematozoa in the blood of a dog These hematozoa are the cause of nagana and tsetse fly disease Renamed Trypanosoma brucei in 1899 David Bruce (1855-1931) Baker (1995)  American Trypanosomiasis = Chagas disease Endemic to Latin America Trypanosoma cruzi Carlos Chagas (1879-1934) Perez et al (2015) Triatoma infestans = kissing bug  Two-host life cycle of Trypanosoma brucei Host#1: Tsetse fly (Glossina) = vector (midgut and salivary glands) Host#2: Human or another mammal (bloodstream) Pays et al. Nature Reviews Microbiology 4, 477–486 (June 2006) | doi:10.1038/nrmicro1428  T. brucei surface coat Monolayer of ~107 molecules of a single glycoprotein (VSG) >1,000 VSG sequences only one VSG variant is produced at any one time VSG contain a variable region Gull Lab, Sir William Dunn School of Pathology  Periodicity of the symptoms At regular intervals, T.brucei switches to a new surface protein  Antigenic variation =a mechanism to escape the host immune response Kelly and Carrington (2018)  Phylogeny of Eukaryotes Diplomonads Excavata Parabasalids Euglenozoans Stramenopiles Alveolates Rhizarians Diatoms Protists are spread throughout Golden algae Brown algae the eukaryotic tree of life “SAR” clade Dinoflagellates Apicomplexans Ciliates Forams Four supergroups: Cercozoans Excavates Radiolarians SAR clade Archaeplastida Archaeplastida Red algae Chlorophytes Green Unikonta algae Charophytes Land plants Amoebozoans Opisthokonts Slime molds Tubulinids Unikonta Entamoebas Nucleariids Fungi Choanoflagellates Animals Archaeplastida Red algae Archaeplastida algae Green Land plants  Primary endosymbiosis: red and green algae cyanobacterium Primary Different pigments Endosymbiosis Red algae Archaeplastida algae Green Acquisition of photosynthesis genes (from cyanobacteria) Land plants Calvin cycle enzymes (e.g., RuBisCo) are identical in all photosynthetic organisms (including red algae, green algae and plants) Pigments may differ Primary endosymbiosis: red and green algae Red alga Red pigment (phycoerythrin) Photosynthetic & chlorophyll a+d eukaryote Cyanobacterium chlorophyll a & phycocyanin Primary Endosymbiosis Heterotrophic eukaryote (with mitochondria) One of these membranes was lost in descendants Green alga Green pigment (chlorophyll a+b)  Red algae Phycoerythrin (absorbs blue light, reflects red light) Can live at great depths (