Microbiology: Blue-Green Algae, Cyanobacteria, and Protists Lecture 3 PDF

# Microbiology: Blue-Green Algae, Cyanobacteria, and Protists ## Lecture 3 - General Microbiology ### Blue Green Algae (Cyanophyta) - Cyanophyta includes a large number of algae that are characterized by a particular organization. - They lack a well-defined nucleus, which is present in other algae...

# Microbiology: Blue-Green Algae, Cyanobacteria, and Protists ## Lecture 3 - General Microbiology ### Blue Green Algae (Cyanophyta) - Cyanophyta includes a large number of algae that are characterized by a particular organization. - They lack a well-defined nucleus, which is present in other algae. - Cyanophyta are characterized by a blue-green coloration of their cells. - The chief pigments are: Chlorophyll, Carotenes, Xanthophyll, C-Phycoerythrin. - The product of photosynthesis is glycogen. - Cyanophyta can withstand unfavorable conditions. - Some Cyanophyta members lead a symbiotic life with fungi, forming lichens. - There is a relationship between blue-green algae and bacteria. - Some authors suggest that both bacteria and blue-green algae may be regarded as two classes of the Phylum Schizophyta. - Cyanophyta lack nuclei, sexual reproduction, and plastids. ### Cell Structure - The cell wall consists of two layers: a thin inner layer and a thick outer, gelatinous layer known as the cell sheath. - The protoplast is differentiated into two parts: 1. A peripheral pigmented region (chromatoplasm). 2. A central colorless region (centroplasm or central body). - This region contains: - Plasma membrane - Protein granules - Nucleoid (circular DNA) - Ribosomes - Gelatinous coat - Photosynthetic lamellae - Phycobilisomes (cyanosomes) - Lipid droplets ### Reproduction - Hormogonia are usually short lengths of trichome with rounded ends and without differentiation of the cells. - Resting spores, or a kinete, are formed. There is an obvious relation between the position of heterocysts and the place of a kinete formation. ### Economic Importance of Cyanobacteria - Blue-green algae like Nostoc, Oscillatoria, Scytonema, and Spirulina are used to fertilize the soil. - Heterocyst-forming Cyanobacteria are specialized for nitrogen fixation and can fix nitrogen gas into ammonia, nitrite, or nitrate, which can be absorbed by plants and converted into protein and nucleic acids. - Cyanobacteria secrete toxic substances into water that lead to water pollution. ### The Eukaryotic Cell (Protists) - Protists are microscopic, unicellular organisms that don’t fit into other kingdoms. - Some members of the kingdom Protista are unicellular, others are colonial, and yet others are multicellular. - Protists are all eukaryotes (they have a true nucleus). - Protists are grouped into three major, unofficial categories based on means by which they obtain nutrition: - Protozoa - Algae - Fungus-like protists ### Animal-like Protists (Protozoa) - Single-celled organisms regarded as having animal-like characteristics. - Commensal: Lives in or on another organism, deriving some benefit from the association but not harming the other part. - Most Protozoans are found in fresh water or marine habitats, where they form a significant component of plankton. - Protozoans ingest their food through phagocytosis. Some have mouth-like structures into which the prey is put, while others use pseudopodia to move and engulf prey. ### Plant-like Protists (The Algae) - Algae are photosynthetic. Their nutrition is plant-like. - Almost all algae have chlorophyll A, most have chlorophyll C, and a few have chlorophyll B. - Algae derive energy from the sun through oxygenic photosynthesis. - Algae fix carbon from dissolved bicarbonate. - All algal types are eukaryotic and therefore contain internal organelles: nuclei, mitochondria, endoplasmic reticulum, ribosomes, Golgi body, and chloroplasts (in most cases). - All algae, with the exception of the Euglenophyta group, have cellulose cell walls which are frequently modified with other polysaccharides, including pectin and alginic acids. - Algae include different groups (phyla or divisions): Euglenophyta, Bacillariophyta, Chlorophyta, Phaeophyta, and Rhodophyta. #### Phylum: Euglenophyta - Euglena are semi-rigid structures composed of protein strips found surrounding the cell of many unicellular Protozoans and algae. - Individuals range in size from 10-500µm. - Euglenophytes are commonly found in freshwater, particularly that with a high organic content and to a lesser extent in soil, brackish water, and salt water. - The storage product of photosynthesis is a β-1,3-linked glucan called paramylon. - Euglenophytes reproduce through fission and cyst formation. #### Division: Bacillariophyta (Diatoms) - Diatoms are commonly known as diatoms. The majority are single-celled, but in some cases, the cells are united into colonies. - Diatoms are found in both fresh and salt water. - Characteristic features of diatoms include: - They possess a diploid thallus. - They have a silicified cell wall consisting of overlapping halves bearing characteristic secondary structures. - They store food reserves as oil and chrysolaminarin, or a protein-like food material called volutin. - They have a motile stage (sperms) with a single flagellum, sometimes two. - They produce a unique type of spore called an autospore. - They contain chlorophyll a and c, along with fucoxanthin, as photosynthetic pigments. ##### Cell Structure - **Valve view:** The valve side is uppermost. The diatom cell is seen from the top or bottom. This is also called the top view. - **Girdle view:** The overlapping bands or girdle is uppermost. This is also called the side view. ##### Cell Division of Diatoms - Cell division occurs as follows: 1. An increase in volume of the frustule occurs, leading to a slight separation of the valve. 2. Mitotic division of the nucleus occurs, with the spindle parallel to the short axis of the cell. 3. Longitudinal division of the protoplast occurs, resulting in the formation of two daughter protoplasts. 4. Each daughter protoplast has half of the old cell wall on one side and the protoplasmic membrane on the other side. 5. The new half wall fits inside the original old half wall in the two newly formed cells. 6. The old wall of the two newly formed cells forms the epitheca, and the new wall always forms the hypotheca. 7. Of the two cells, one (with the old epitheca) will have the same size as that of the parental cell, while the other (with the old hypotheca) will be slightly smaller. 8. Over time, repeated cell division results in a decrease of the size of diatom cells.