Microbial Diversity and Diversification PDF

Microbial Diversity and Diversification As you saw in the graphic just before this page, animals make up a very small proportion of the biomass on the planet! After plants, Bacteria make up the most biomass at 70 Gt C. Archaea make up 7 Gt C and Protists make up 4 Gt C, which is still more than anim...

Microbial Diversity and Diversification As you saw in the graphic just before this page, animals make up a very small proportion of the biomass on the planet! After plants, Bacteria make up the most biomass at 70 Gt C. Archaea make up 7 Gt C and Protists make up 4 Gt C, which is still more than animals. What makes these figures even more impressing is that all three groups are microscopic single-celled organisms! Recall from the history of life on earth activity that prokaryotic cells represented the first form of biological life on the planet. Then eukaryotic cells evolved from prokaryotic cells. Take a moment and review the difference between prokaryotes and the first eukaryotes (protists). *Note: Eukaryote examples are missing all of the animals! Prokaryotes We don't have a lot of prokaryotic specimens to look at in lab; many look similiar morphologically and can only be distinguished with stains that look for certain molecules in their cell walls. In lecture, you will learn about the bacteria diversity associated with our microbiomes and soil. Prokaryotes do not have sexual reproduction, rather they multiply via fission (cell division). They are capable, however, of sharing genetic material through conjugation, transduction, and transformation. These mechanisms are known as horizontal gene transfer (as opposed to vertical gene transfer) since they occur among individuals from the same generation and not from parents to offspring. Because of horizontal gene transfer, speciation looks very different than it does in sexually reproducing species. In fact, the biological species concept doesn't apply to prokaryotes! When a prokaryote cell acquires new genes through this process, it is technically different than the cell it was derived from and it can potentially be classified as a new species. This Radio lab episode is a fun way to learn more: Radio Lab: Infective Heredity (https://www.wnycstudios.org/podcasts/radiolab/articles/infective-heredity) Eukaryotes Hopefully you remember from Bio 10A that eukaryotic cells evolved from prokaryotic cells through a process called endosymbiosis. Among other features, chloroplasts and mitochondria are organelles that distinguish eukaryotes from prokaryotes. In fact, they used to be free living prokaryotes before they evolved into organelles. This image shows this process happening several times in the evolution of photosynthetic protists (simple eukaryotes). Lynn Margulis published this theory of endosymbiosis in the paper: Sagan, L. (1967). On the origin of mitosing cells. Journal of theoretical biology, 14(3), 225-IN6. Unbeknownst to Lynn at the time, the Russian biologist Konstantin Merezhkovsky had published a similar proposal as early as 1905. However, Merezhkovsky’s ideas were largely ridiculed or forgotten, and when Margulis resurrected them, criticism was harsh. Some 15 journals rejected her first paper on endosymbiosis before it was published. Now biologists accept it as one of the great advances of the 20th century and there is overwhelming evidence to support its ability to explain the evolution and diversification of eukaryotic life. Endosymbiosis is the process by which an engulfed proteobacteria evolved into the organelle we call the mitochondrion. Mitochondria allow cells to undergo cellular respiration which increases the amount of energy available for movement and increased complexity. Check out this Radio lab episode Cellmates (https://www.wnycstudios.org/podcasts/radiolab/articles/cellmates) to learn about why prokaryotes dominated the planet for so long and the reason why endosymbiosis is so significant to the evolution of multicellular eukaryotes. Ecological diversity in protists The classification of protists has been in flux since the dismantling of Kingdom Protista. Genetic information has revealed that some protists are more closely related to multicellular groups than they are to each other. The classification is likely to continue to be in flux as new information is discovered. Nevertheless, in lab you will look at representative specimens from the 4 supergroups picture below. I've included some more commonly known examples and their ecological roles. Excavata: Giardia lamblia can be found in freshwater streams and is an intestinal parasite that causes severe diarrhea when ingested. Trypanosoma brucei develops in the gut of the tsetse fly after the fly bites an infected human or other mammalian host. The parasite then travels to the insect salivary glands to be transmitted to another human or other mammal when the infected tsetse fly consumes another blood meal. T. brucei is common in central Africa and is the causative agent of African sleeping sickness, a disease associated with severe chronic fatigue, coma, and can be fatal if left untreated. Euglena, encompasses some mixotrophic species that display a photosynthetic capability only when light is present. In the dark, the chloroplasts of Euglena shrink up and temporarily cease functioning, and the cells instead take up organic nutrients from their environment. SAR clade: The genus Plasmodium, causes causes malaria in humans. It has an apical complex that is specialized for entry and infection of host cells. Indeed, all apicomplexans are parasitic. Apicomplexan life cycles are complex, involving multiple hosts and stages of sexual and asexual reproduction. Dinoflagellates exhibit extensive morphological diversity and can be photosynthetic, heterotrophic, or mixotrophic. Many are encased in cellulose armor and have two flagella that fit in grooves between the plates. These protists exist in freshwater and marine habitats, and are a component of plankton. Some dinoflagellates generate light, called bioluminescence, when they are jarred or stressed. Large numbers of marine dinoflagellates (billions or trillions of cells per wave) can emit light and cause an entire breaking wave to twinkle or take on a brilliant blue color. For approximately 20 species of marine dinoflagellates, population explosions (also called blooms) during the summer months can tint the ocean with a muddy red color. This phenomenon is called a red tide, and it results from the abundant red pigments present in dinoflagellate plastids. In large quantities, these dinoflagellate species secrete an asphyxiating toxin that can kill fish, birds, and marine mammals. The ciliates, which include Paramecium and Tetrahymena, are a group of protists 10 to 3,000 micrometers in length that are covered in rows, tufts, or spirals of tiny cilia. By beating their cilia synchronously or in waves, ciliates can coordinate directed movements and ingest food particles. The diatoms are unicellular photosynthetic protists that encase themselves in intricately patterned, glassy cell walls composed of silicon dioxide in a matrix of organic particles. These protists are a component of freshwater and marine plankton. During periods of nutrient availability, diatom populations bloom to numbers greater than can be consumed by aquatic organisms. The excess diatoms die and sink to the sea floor where they are not easily reached by saprobes that feed on dead organisms. As a result, the carbon dioxide that the diatoms had consumed and incorporated into their cells during photosynthesis is not returned to the atmosphere. The brown algae are primarily marine, multicellular organisms that are known colloquially as seaweeds. Giant kelps are a type of brown algae. Some brown algae have evolved specialized tissues that resemble terrestrial plants, with root-like holdfasts, stem-like stipes, and leaf-like blades that are capable of photosynthesis. Foraminiferans, or forams, are unicellular heterotrophic protists, ranging from approximately 20 micrometers to several centimeters in length, and occasionally resembling tiny snails. As a group, the forams exhibit porous shells, called tests that are built from various organic materials and typically hardened with calcium carbonate. The tests may house photosynthetic algae, which the forams can harvest for nutrition. Foram pseudopodia extend through the pores and allow the forams to move, feed, and gather additional building materials. Typically, forams are associated with sand or other particles in marine or freshwater habitats. Foraminiferans are also useful as indicators of pollution and changes in global weather patterns. A second subtype of Rhizaria, the radiolarians, exhibit intricate exteriors of glassy silica with radial or bilateral symmetry. Needle-like pseudopods supported by microtubules radiate outward from the cell bodies of these protists and function to catch food particles. The shells of dead radiolarians sink to the ocean floor, where they may accumulate in 100 meter-thick depths. Preserved, sedimented radiolarians are very common in the fossil record. Archaeplastida: Red algae, or rhodophytes, are primarily multicellular, lack flagella, and range in size from microscopic, unicellular protists to large, multicellular forms grouped into the informal seaweed category. Green algae (chlorophytes and charophytes) exhibit great diversity of form and function. Chlorophytes primarily inhabit freshwater and damp soil, and are a common component of plankton. Chlamydomonas is a simple, unicellular chlorophyte with a pear-shaped morphology and two opposing, anterior flagella that guide this protist toward light sensed by its eyespot. The chlorophyte Volvox is one of only a few examples of a colonial organism, which behaves in some ways like a collection of individual cells, but in other ways like the specialized cells of a multicellular organism. Unikonta: The amoebozoans characteristically exhibit pseudopodia that extend like tubes or flat lobes, rather than the hair-like pseudopodia of rhizarian amoeba. The Amoebozoa include several groups of unicellular amoeba-like organisms that are freeliving or parasites. Choanoflagellates include unicellular and colonial forms, and number about 244 described species. These organisms exhibit a single, apical flagellum that is surrounded by a contractile collar composed of microvilli. Early evolution in the tree of life does not show a dichotomous branching pattern rather it was dominated by horizontal gene transfer as well as serial endosymbiosis, which is represented by the crisscrossing branches. Brunk, C. F., & Martin, W. F. (2019). Archaeal histone contributions to the origin of eukaryotes. Trends in Microbiology, 27(8), 703-714.