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Morphology and Fine Structure of Bacteria

Gross morphology of bacterial cells (great variations—100X)

            Units of measurement                um = 1/1000 mm = 1/1000000 m

                        Ocular micrometer--stage micrometer

            Size

                        Common bacteria  0.5 to 1.0 X 2.0 to 5.0 um

                                    extremes:  100 X 1.0 to 2.0 um

0.1  to 0.3 um--mycoplasmas

pleomorphic

                        Weight--1 trillion = 1 gram

                        Surface area/volume ratio

                                    increased exposure to environment

                                    increased metabolism and growth

            Shape

                        Cocci (coccus--singular)  spherical or ellipsoidal

                        Bacilli (bacillus--singular)  rod-like or cylindrical

                        Spirilla (spirillum--singular)  spiral-shaped

            Arrangement--predominant arrangements are taxonomic characteristic

                        diplococci--uniplanar--pairs

                        streptococci--uniplanar--chains

                        tetracocci--biplanar--four cells

                        staphylococci--triplanar--“bunches”

                        sarcinae--triplanar--cuboidal

                        vibrios--comma-shaped--modified spirilla

                        palisade layer

                        rosette

                        chain

Fine Structure of Bacterial Cells

            Flagella--motility

                        basal body, hook-like segment, filamentous structure

                        flagellin (protein subunit)            10 to 20 nm diameter

                        found in bacilli and spirilla

                        types of flagella

                                    monotrichous--single

                                    lophotrichous--cluster

                                    peritrichous--surrounding

            Pili (fimbriae)    common among Gram negative bacteria

                        ultramicroscopic

                        functions:

                                    F pilus (sex pilus) transfer structure-mating attachment

     

Capsules (slime layer)

                        outside of the cell wall

                        influenced by medium in which bacteria is grown

                        secreted by cell (viscous)          resists dissolution

                        functions:

                                    protective covering

                                    reservoir of stored food

                                    increase infective capacity of bacteria

                                                loss of capsule decreases virulence

            Sheaths--freshwater and marine bacteria

                        insoluble metal compounds--ferric and manganic oxides

                        precipitate around cells due to metabolic activity

            Stalks--freshwater and marine bacteria

                        semirigid adhesive appendage

            Cell Wall--rigidity

                        withstands pressure, temperature, severe conditions

                        thickness—10 to 35 nm—10 to 40% dry weight

                        essential for growth and cell division

                        chemical composition

                                    peptidoglycans--polymers

                                                building blocks

                                                            N-acetylglucosamine (AGA)

                                                            N-acetylmuramic acid (AMA)

                                                            peptide—4 to 5 amino acids

                                                                        L-alanine

                                                                        D-alanine

                                                                        D-glutamic acid

                                                                        lysine

                                                                        diaminopimelic acid

                                                other chemical constituents

                                                            teichoic acid

                                                            diaminopimelic acid

                                                            protein polysaccharides

                                                            lipoproteins

                                                            lipopolysaccharides

                                    differences in composition and structure

                                                Gram positive vs. Gram negative

 

 

 

 

 

 

 

 

 

Structures within the cell wall:

                        Cytoplasmic membrane (7.5 nm)

                                    controls passage of substances across membrane

                                                diffusion, osmosis, active transport

                        Mesosome--invagination of cytoplasmic membrane

                                    continuous with cell membrane

                                    invaginates prior to cell division

                                    functions:

                                                cell wall synthesis

                                                division of nuclear material

                        Cytoplasm--regionalized

                                    cytoplasmic area—RNA, ribosomes, protein synthesis

                                    chromatinic area—DNA, genome

                                                mesosome-cytoplasmic membrane system

                                                circular chromosome--chromatin body

                                    fluid portion—nutrients, inclusion bodies

                                                starch, glycogen, lipids, polyphosphates

 

Protoplasts and Spheroplasts

            Protoplasts--bacteria void of cell wall--flaccid

                        osmotic shock--osmotic gradient

            Spheroplasts--peptidoglycan outer layer removed

                        not completely cell-wall-free

 

Spores--metabolically dormant bodies

            Capable of producing vegetative cell under certain conditions

            Exospores--external spores--chains of spores (conidia)

            Endospores--unique to bacteria

                        endospore formation:

1)      realignment of DNA into filaments-forespore

2)      development of forespore cover

spore cortex--spore coat

3)      release of free spore (parental cell lysis)

Composition:

            dipicolinic acid—5 to 10% dry weight

            calcium

            cortical layer--resistant to temp. & moisture

                        Calcium-dipicolinic acid-peptidoglycan

Vegetative cell production from spore

1)      activate by heat or aging

2)      germination

3)      growth

Taxonomic implications

            centrally located spores

            terminally located spores

                                    subterminally located spores

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