2The Prokaryotic CellMembers of the prokaryotic world make up a vast heterogeneous group of very small single-celled organisms.Include bacteria and archae, although the majority are bacteriaThe thousands species of bacteria are differentiated by many factors such as:Morphology (shape), chemical composition (often detected by staining reactions), nutritional requirements, biochemical activities, and sources of energy (sunlight or chemicals)These differences can only be seen with the use of a microscope
3Size, Shape, and Arrangement Bacteria come in many sizes, and several shapes.Most range from 0.2 to 2.0 µm in diameter and 2-8 µm in lengthBasic shapes include:Cocci- round shapedBacillus- rod shapedSpirillum- spiral shaped, helical shape like corkscrew, have rigid bodies, and use flagella to moveVibrio- curvedSpirochetes- helical and flexible, move by axial filaments found within flexible external sheathSquareStar
4Cell Cluster Formation StreptobacillusBacteria are also classified according to cell cluster formation:Cluster formationDescriptionDiplococciTwo cocci cells pairedStaphylococciNumber of cells clustered together (grape-like)Streptococci & StreptobacillusNumber of cells arranged in a chainStaphylobacilli do not exist because bacilli only divide along their long axis which means they will never form clusters of rods.
5Learning Check: What Shape are these bacteria? 1.2.3.bacillusspirillumcoccus5.6.spirochetevibriobacillus
6Shape and Arrangement The shape of bacteria is determined by heredity. Most bacteria are monomorphic: maintain a single shapeEnvironmental factors can alter that shapeSome bacteria like Rhizobium and Corynebacterium are pleomorphic: can have many shapes, not just one.Source for figure:
7Basic Components of Bacteria Cell wall-this gives the cell its shape and retains the constituentsCell membrane-used for filtering in food constituents and discharging waste productsNucleoid-where the genetic material of the cell is stored;Cytoplasm- a semiliquid proteinaceous substance which contains starch, fat and enzymes.*Cell wall- Most bacteria have a cell wall but there are some that do not like Mycoplasma species
8Structures External to the Cell Wall Possible structures external to the prokaryotic cell wall are:GlycolaxFlagellaAxial filamentsFimbraeand PiliIn certain species, capsules are important in contributing to bacterial virulence (the degree to which a pathogen causes disease). Capsules often protect pathogenic bacteria from phagocytosis by the cells of the host. For example Streptococus pneumoniae which causes pneumonia only when the cells are protected by a polysaccharide capsule
9What is the Glycocalyx?Means sugar coat & is the general term used for substances that surround cellsBacterial glycocalyx is a viscous (sticky), gelatinous polymer that is external to the cell wallComposed of a polysaccharide, polypeptide, or bothTwo types:Capsule: substance is organized and is firmly attached to the cell wallSlime layer: substance is unorganized and only loosely attached to the cell wall glycocalyxFig. 1Polysaccharide: a carbohydrate (e.g., starch, cellulose, or glycogen) whose molecules consist of a number of sugar molecules bonded together.Polypeptide: a linear organic polymer consisting of a large number of amino-acid residues bonded together in a chain, forming part of (or the whole of) a protein molecule.Source for Fig. 1:
10(a) Micrograph of Streptococcus pneumoniae, the common cause of pneumonia, showing a prominent capsule. (b) Bacteroides, a common fecal bacterium, has a slime layer surrounding the cell
12Learning CheckWhat advantage does a glycocalyx provide a cell? (think about its composition)
13Glycocalyx Very important component of biofilms Biofilms are densely packed communities of microbial cells that grow on living or inert surfacesA glycocalyx that helps cells in a biofilm attach to their target environment and to each other is called an extracellular polymeric substance (EPS)EPS protects the cells within itFacilitates communication among themand enables the cells to survive by attaching to various surfaces in their natural environmentFig. 2Through attachment, bacteria can grow on diverse surfaces such as rocks in fast-moving streams, plant roots, human teeth. Streptococcus mutans, an important cause of dental cavities, attaches itself to the surface of teeth by a glycocalyx. Vibrio cholerae, the cause of cholera produces a glycocalyx that helps it attach to the cells of the small intestine.Source for Fig. 2
14FlagellaSome prokaryotes have flagella which are long filamentous appendages that propel bacteriaPeritrichous: flagella distributed over the entire cellPolar: at one or both poles or ends of the cellMonotrichous: A single flagellum at one poleLopothrichous: a tuft of flagella coming from one poleAmphitrichous: flagella at both poles of the cellBacteria that lack flagella re referred to as atrichous (without projections)Motility enables a bacterium to move toward a favorable environment or away from an adverse on. This is called taxis. Motile bacteria contain receptors in various locations which pick up chemical stimuli, such as oxygen, ribose.
15Flagellar MovementThe ﬂow of hydrogen ions (H ) or of sodium ions (Na ) through the cytoplasmic membrane near the basal body powers the rotation, propelling the bacterium through the environment at about 60 cell lengths per second—equivalent to a car traveling at 670 miles per hourFigure 3.9 Motion of a peritrichous bacterium. In peritrichous bacteria, runs occur when all of the ﬂagella rotate counterclockwise and become bundled. Tumbles occur when the ﬂagella rotate clockwise, become unbundled, and the cell spins randomly. In positive chemotaxis (shown), runs last longer than tumbles, resulting in motion toward the chemical attractant.
16Axial Filaments Spirochetes have unique structure and motility Move my means of axial filamentsBundles of fibrils that arise at the ends of the cell beneath an outer sheath and spiral around the cellThe rotation of the filaments produces a movement of the outer sheath that propels the spirochetes in a spiral motion
17Fimbriae and PiliMany gram-negative bacteria contain hair-like appendages that are shorter, straighter, and thinner than flagellaare used for attachment and transfer of DNA rather than for motilityFimbrae can occur at the poles of the bacterial cell or entire surface of cellHave a tendency to adhere to each other and to surfacesPili are usually longer than fimbrae but shorter than flagella and are found as one or two per cellInvolved in motility and DNA transfer
19Learning Check Several Escherichia coli cells are connected by conjugation pili. How are pili different from bacterial ﬂagella?Bacterial ﬂagella are ﬂexible structures that rotate to propel the cell; pili are hollow tubes that mediate transfer of DNA from one cell to another