Bacterial Morphology and Bacterial Morphology and Structure Structure Xiao-Kui Guo PhD http://basic. shsmu . edu . cn / passw /micro2/index.asp
Bacterial Morphology and StructureBacterial Morphology and Structure
Xiao-Kui Guo PhD
http://basic.shsmu.edu.cn/passw/micro2/index.asp
SIZE OF BACTERIASIZE OF BACTERIA Unit for measurement :
Micron or micrometer,μm: 1μm=10-3mm
Size:
Varies with kinds of bacteria, and also related to their age and external environment.
Cocci: sphere, 1μm Bacilli: rods , 0.5-1 μm in width -3 μm in length Spiral bacteria: 1~3 μm in length and 0.3-0.6 μm in width
Structure of BacteriaStructure of Bacteria
Particular structures capsule 荚膜flagella 鞭毛
pili 菌毛spore 芽胞
Essential structures Essential structures cell wall cell wall 细胞壁细胞壁
cell membrane cell membrane 细胞膜细胞膜Cytoplasm Cytoplasm 细胞质细胞质
nuclear materialnuclear material 核质核质
Gram +
Gram -
Cell wall
Cell (inner) membrane Outer membraneRibosomes
Granule
Cell wall
NucleoidCell membrane
Capsule
Flagellum
Pili
Gram, C. 1884. Ueber die isolirte Gram, C. 1884. Ueber die isolirte Farbung der Schizomyceten in Farbung der Schizomyceten in SchnittÄund Trockenpraparaten. SchnittÄund Trockenpraparaten. Fortschritte der MedicinFortschritte der Medicin, Vol. 2, pages , Vol. 2, pages 185-189.185-189.
1884: 1884: Christian GramChristian Gram: First publication for the Gram stain method) : First publication for the Gram stain method) Editor's note: I would like to testify that I have found the Gram method to be one ofEditor's note: I would like to testify that I have found the Gram method to be one ofthe best and for many cases the best method which I have ever used for stainingthe best and for many cases the best method which I have ever used for staining Schizomycetes.Schizomycetes.
Cell wallCell wall Situation:
outmost portion. 15-30nm in thickness, 10%-25% of dry weight.
Cell wallCell wall : :Common peptidoglycan Common peptidoglycan layerlayer
A backbone of N-acetyl glucosamine and N-acetylmuramic acid: Both discovered in Gram positive and Gram negative bacteria.
A set of identical tetrapeptide side chain attached to N-acetyl-muramic acid: different components and binding modes in Gram positive and Gram negative bacteria.
A set of identical peptide cross bridges: only in Gram positive bacteria
Special components of Special components of Gram positive cell wallGram positive cell wall
Teichoic acid
SPA / M POTEIN
Special components of Gram Special components of Gram
negative cell wallnegative cell wall
FunctionsFunctions of Cell Wall of Cell Wall Maintaining the cell's characteristic shape- the rigid
wall compensates for the flexibility of the phospholipid membrane and keeps the cell from assuming a spherical shape
Countering the effects of osmotic pressure Providing attachment sites for bacteriophages Providing a rigid platform for surface appendages-
flagella, fimbriae, and pili all emanate from the wall and extend beyond it
Play an essential role in cell division Be the sites of major antigenic determinants of
the cell surface 。 Resistance of Antibiotics
Wall-less forms of Wall-less forms of BacteriaBacteria..
When bacteria are treated with 1) enzymes that are lytic for the cell wall e.g. lysozyme or 2) antibiotics that interfere with biosynthesis of peptidoglycan, wall-less bacteria are often produced.
Usually these treatments generate non-viable organisms. Wall-less bacteria that can not replicate are referred to as spheroplasts (when an outer membrane is present) or protoplasts (if an outer membrane is not present).
Occasionally wall-less bacteria that can replicate are generated by these treatments (L forms).
Cell Cell membranemembrane
• Site of biosynthesis of DNA, cell wall polymers and membrane lipids. Selective permeability and transport of solutes into cells
• Electron transport and oxidative phosphorylation• Excretion of hydrolytic exoenzymes
MesosomesMesosomes
• Mesosomes are specialized structures formed by convoluted inveigh-nations of cytoplasmic membrane, and divided into septal and lateral mesosome.
CytoplasmCytoplasm Composed largely of water, together with proteins, nucleic
acid, lipids and small amount of sugars and saltsRibosomes: numerous, 15-20nm in diameter with 70S;
distributed throughout the cytoplasm; sensitive to streptomycin and erythromycin site of protein synthesis
Plasmids: extrachromosomal genetic elements
Inclusions: sources of stored energy, e,g volutin
PlasmidPlasmid Plasmids are small , circular/line , extrachromosomal, double-stranded DNA molecules 。 They are capable of self-replication and contain genes that confer some properties , such as antibiotic resistance , virulence factors 。 Plasmids are not essential for cellular survival. Inclusions of Inclusions of
BacteriaBacteria
Inclusions are aggregates of various compounds that are normally involved in storing energy reserves or building blocks for the cell. Inclusions accumilate when a cell is grown in the presence of excess nutrients and they are often observed under laboratory conditions.
granulose
NucleusNucleus
Lacking nuclear membrane, absence of nucleoli, hence known as nucleic material or nucleoid, one to several per bacterium.
Capsules and slime layersCapsules and slime layers
These are structures surrounding the outside of the cell envelope. They usually consist of polysaccharide; however, in certain bacilli they are composed of a polypeptide (polyglutamic acid). They are not essential to cell viability and some strains within a species will produce a capsule, whilst others do not. Capsules are often lost during in vitro culture.
Attachment Protection from phagocytic
engulfment. Resistance to drying. Depot for waste products. Reservoir for certain
nutrients. protection
FlagellaFlagella
Monotrichate/Amphitrichate/Lophotrichate/Peritrichate
Identification of Bacteria
Pathogenesis Motility of
bacteria
Some bacterial species are mobile and possess locomotory organelles - flagella. Flagella consist of a number of proteins including flagellinThe diameter of a flagellum is thin, 20 nm, and long with some having a length 10 times the diameter of cell. Due to their small diameter, flagella cannot be seen in the light microscope unless a special stain is applied. Bacteria can have one or more flagella arranged in clumps or spread all over the cell.
PiliPili
Pili are hair-like projections of the cell , They are known to be receptors for certain bacterial viruses. Chemical nature is pilin
Classification and Function
a. Common pili or fimbriae: fine , rigid numerous, related to bacterial adhesion
b. Sex pili: longer and coarser, only 1-4, related to bacterial conjugation
Endospores Endospores (spores)(spores)
• Dormant cell Dormant cell • Resistant to adverse Resistant to adverse
conditions conditions - high temperatures- high temperatures- organic solvents- organic solvents
• Produced when starvedProduced when starved• Contain calcium dipicolinateContain calcium dipicolinate DPA, DPA, DDipicolinic acidipicolinic acid• BacillusBacillus and and ClostridiumClostridium
Identification of Bacteria
Pathogenesis Resistance
Microscope Light Microscope Electron Microscope Darkfield Microscope Phase Contrast Microscope Fluorescence Microscope Cofocal Microscope )
Methods
Staining Methods
Simple staining; Differential staining ( Gram
stain, Acid-fast stain), Special staining( Negative stain,
Spore stain, Flagella stain)