Lecture 1 Bacterial Classification and Morphology Morphology is the study of organistic structure Physiological the study of a function of an organism Criteria for Classification Macroscopic can see w naked eye colony morphology Microscopic need microscope cell shape staining properties etc Physiological presence absence of particular enzymes Chemical Analysis not used so much Decomposes bacteria puts in blender to find what substances make it up Serological use of antibodies Genetic G C rRNA chromosome gene sequence Morphology of Bacterial Cells Most common cell shapes coccus cocci spherical perfect spheres bacillus bacilli rod perfect rods Also coccobacillus short rod vibrio short curved rod spirillium spiral rod these have morphologies shapes and look similar pleomorphic variable shape each cell look different etc Pathology Relationship to pathology ask yourself would you rather be infected with a bacterium virus with a particular characteristic or without Strictly speaking bacterial cell shape does not correlate with pathology Grouping of Bacterial Cells Bacterial cells divide by a process known as binary fission which is a more simple process than Mitosis more on this later Some bacterial cells remain loosely attached following nuclear fission cell division forming arrangements characteristic of their genus and species This occurs more often in cocci than in bacilli Prokaryotic cells bacteria reproduce primarily by binary fission Binary fission a simple process of cells splitting equally into two Some bacteria are surrounded by an extracellular layer called a sheath This sheath also holds bacterial cells together after cell division Long Chains filamentous groupings of 2 diplococci any coccus that forms big clumps is staphylococcus Grouping AND Pathology both good news and bad news An organism that forms groups Spreads more slowly good news Can hide from the Immune System longer bad news explain delays immune responses Bacterial Cell Structure Flagella allow bacteria to move from one place to another bacterial propellers Flagella Flagella provide the power of motility This allows cells to swim freely through an aqueous habitat Under a microscope they display three distinct parts the filament helical structure composed of a protein called falgellin the hook is anchored to the cell by the basal body a stack of rings firmly anchored through the cell wall to the cell membrane o monotrichous single o lophotrichous bunches tufts groups o amphitrichous both poles at either end o peritrichous all over surface Flagella vary both in number and arrangement according to 2 patterns 1 in a polar arrangement the flagella are attached at one or both ends of a cell 3 subtypes are monotrichous with a single flagellum lophotricphous with small bunches or tufts of flagella emerging from the same site amphitrichous with flagella at both poles of the cell 2 peritrichious arrangement flagella are dispersed randomly over the surface of the cell Flagella can detect and move in response to chemical signals a type of behavior called chemotaxis positive chemotaxis is movement of a cell in the direction of a favorable chemical stimulus usually a nutrient negative chemotaxis is movement awayfrom a repellent potentially harmful compound Flagella can guide bacteria in a certain direction b c the system for detecting chemicals is linked to the mechanisms that drive the flagellum Taxis the capabili to move toward or away from a stimulus Chemotaxis directional movement toward away from chemical stimuli ex toward food and oxygen and away from stimuli such as chemical toxins Magnetotaxis north and south and up and down Often live in aquatic sentiments and find that too much oxygen can be toxic Direct their rotating flagella to carry them into deeper layers of sentiments for deeper nutrients they require Located in the cell membrance are clusters of receptors that bind specific molecules coming from the immediate environment The attachement of sufficient numbers of these molecules transmits signals to the flagellum and sets it into rotary motion If several flagellum are present they become aligned and rotate as a group As a flagellum roatates counterclockwise the cell itself swims in a smooth linear direction toward the stimulus This action is call run Runs are interrupted as various intervals by tumbles caused by the flagellum reversing its direction This makes the cell stop and change its course It is believed that attractant molecules inhibit tumbles increase runs and permit progress toward stimulus Repellents cause numerous tumbles Allowing the bacterium to redirect itself away from the stimulus Some photosynthetc bacteria exhibit phototaxis a type of movement in response to light rather than chemicals Other Appendages Fimbrae and Pili both refer to bacterial surface appendages that are involved in interactions with other cells but do not provide locomotion Fimbrae small bristlelike fibers emerging from the surface of many bacterial cells Their exact composition varies but most of them contain protein Fimbrae have an inherent tendency to stick to each other and to surfaces They maybe responsible for the mutual clinging of cells that leads to biofilms and other thick aggregates of cells on the surface of liquids and for the microbial colonization of inanimate solids such as rocks and glass Some pathogens can colonize and infect host tissues because of tight adhesion between their fimbrae and epithelial cells EX gonoccus agent of gonorrhea conlonizes the genitourinary tract and E Coli colonizes the intestine by this means Pili a pilus is an elongated rigid tubular stucture made of speical protein pilin True pili have been found only on gram negative bacteria where they are utilized in mating process between cells called conjugations which involves partial transfer of DNA from one cell to another A pilus from a donor cells unites with a recipent cell thereby providing a cytoplasmic connection for making the transfer Slime layer A loose gel like layer usually composed of polysaccharide that functions to protect from water and nutrient loss and in adhesion Streptococcus mutans dental plaque also biofilms Capsule thick tightly bound coating that helps the bacterium evade phagocytosis lycocalyx develops as a coating of macromolecules to protect the cell and in some cases help it adhere to its environment Glycocalyces differ among bacteria in thickness organization and chemical composition Some Glycocalyx bacteria