protists (Lec 6).pdf

Amoebae • One macronucleus • Most are aerobic • Most are heterotrophic – Some mixotrophic • Asexual reproduction only – No specific fission plane • Some move, some are stationary • Most publicised protozoan Four Eukaryote Supergroups Excavata SAR Archaeplastida Unikonta Naked amoebae • Amoeb...

Amoebae • One macronucleus • Most are aerobic • Most are heterotrophic – Some mixotrophic • Asexual reproduction only – No specific fission plane • Some move, some are stationary • Most publicised protozoan Four Eukaryote Supergroups Excavata SAR Archaeplastida Unikonta Naked amoebae • Amoeba proteus • Move by cytoplasmic streaming • Produce pseudopodia on surfaces Naked amoebae • Feed by direct interception of prey • Raptorial feeding • No specific location for ingestion – can be anywhere Naked amoebae – 3 cell forms • Trophozoites - the feeding form • Cysts – all produce a resting stage • Floating form – stiffened pseudopodia for dispersal Shelled amoebae • Enclosed in a shell (‘test’) • Shell can be made of anything • Intrashellular cytoplasm within test • Project extrashellular cytoplasm to move and/or feed • Raptiorial or diffusion feeding • Can produce cysts https://youtu.be/9EutjfddS2c Testate amoebae Freshwater, Marine and Terrestrial Raptorial Foraminiferans Marine only CaCO3 tests Diffusion Diffusion feeding • Stationary predator captures prey with sticky extrashellular cytoplasm (‘axopodia’) Radiolarians Marine only Silica tests Diffusion Heliozoans Freshwater Silica tests Diffusion Summary of Protists • Single-celled eukaryotes • Ciliates, flagellates and amoebae • Move with cilia, flagellar or cytoplasmic streaming • Predominantly divide asexually • Feed by • Photoautotrophy, heterotrophy & mixotrophy • Heterotrophy via • Raptorial, filter or diffusion feeding • Some produce cysts Ecological impact Campbell p668-9 • In the environment – they are everywhere • Good = all of the protists • Microbes: base of every food chain • Keep bacterial populations healthy • Important in nutrient cycling • Bad = mainly amoebae • Allow the evolution of new bacterial pathogens • Act as a ‘reservoir’ for them too Good ecological impact “The Microbial Loop” Aerobic CO2 Photoautotrophs N&P DOC Heterotrophic Protozoa Bacteria N&P DOC: Dissolved organic carbon (sugars) N: Nitrogen P: Phosphorus Metazoa Log (Number of cells) Predation stops bacteria reaching ‘stationary phase’ Time (hours) Predation keeps bacteria in ‘log phase’: Bacteria are constantly feeding and dividing so they are constantly ‘active’. FEEDING leads to REMINERALISATION Cytoplasm Prey CO2 (respiration) Solid waste Food Vacuole (organic CNP) (Phagosome) (organic CNP) PO4 and NH4 Protists have to maintain their cellular C:N:P ratio at 50:10:1 Bad ecological impact – evolution of pathogens • Particularly evident in amoebae • Amoebae and macrophages share many similarities • Bacteria practice evading digestion in amoebae • Become pathogenic and evade our immune system Digestion in paramecium Evading digestion in amoebae Amoebae – ‘Trojan horses’ • Amoebae become a reservoir for pathogenic bacteria – e.g. Legionella, Salmonella etc Brock p1042 Steps in infectious disease Reservoir Transport to host Tissue damage Adherence & Colonisation Invasion of tissues Evasion of host defense Humans • 90% of human cells are bacterial • One protist naturally present • Amoeba • Entamoeba coli • Exists in the gut – not pathogenic • Gut is the site of most bacteria • Attractive location for parasitic protists Gut infections caused by protists • Amoebae e.g. Entamoeba histolytica • One ciliate – Balantidium coli • Flagellates e.g. Giardia lamblia • Dysentery • All produce cysts • Reservoir: Water and animals/humans • Transport: Contaminated water, Faecal-oral route • Treatable – but takes months due to intermittent cysts Steps in infectious disease BROCK p1064-1070 Reservoir Transport to host Tissue damage Adherence & Colonisation Invasion of tissues Evasion of host defense Eye infection caused by protists • Amoebae belonging to genus Acanthamoeba • Causes Keratitis • Reservoir: Water • Transport: Dirty contact lenses • Treatable (but can lead to glaucoma) H2O2 must be in contact lens cleaner Brain infection caused by protists • One amoeba – Naegleria fowleri • ‘Brain eating amoeba’ • Primary Amoebic Meningoencephalitis (PAM) • Reservoir: Warm water • Unusual flagellate stage • Transmission: Flagellate swims up nose • Fatal (in two weeks) Sexually transmitted disease (STDs) • One flagellate – Trichomonas vaginalis • Trichomoniasis • Anaerobic and no cysts • Infects urethra, vagina, prostate • Reservoir: Humans • Males are asymptomatic • Transmission: Sexual intercourse • Treatable Blood/tissue infections caused by protists • Flagellates e.g. Leishmania mexicana • Leishmaniasis • Aerobic, no cysts • Reservoir: Dogs • Transmission: Sand fly (Vector) • ‘Visceral’: attacks tissues e.g. spleen and liver • ‘Cutaneous’: Infects macrophages and divides within • Treatable BIOL123: malaria and sleeping sickness