Morphology of bacteria

    Size:

• Bacteria are invisible to human eyes and are measured in micro meters
• Size varies depending upon the species, but most are approximately 0.5-1.0 micro meter in diameter. e.g. streptococci are spherical bacteria with diameters ranging from 0.75-1.25 micro meters.
• Cells of some species are 0.5-2.0 micro meter in diameter but but more than 100 micro meter in length a meters ranging from 0.75-1.25 micro meters.
• Calculations show that approximately 1 trillion (1,000,000,000,000) bacterial cells weigh a mere 1 gram.  They usually viewed at a magnification of 1000 times.
  The ratio of surface area to volume for bacteria is high compared with that of larger organisms of similar shape.
  
  
  
  
  
  

  Shape:

  
  Individual bacterial cells have one of the three basic shapes. They are:
       
   Cocci: they are spherical in shape.they are usually round or can be ovoid to flattened on one side when they are adhering to one another.  e.g. Staphylococcus aureus, Streptococcus spp
  
  
       Bacilli:cylindrical or rod like cells are called bacilli. There are considerable differences in the length and width of different species of bacilli. The ends of some are rounded and others may be pointed. Bacillus subtilis
  
  
      Spirilla: they look like cork screw and are spiral or helical. For example: Aquaspirillum itersonii
  
  
  
  
  
  

  Bacterial reproduction

  Prokaryotes mainly reproduce in two ways:
    
          1. Asexual reproduction:
                              a) binary fission
                              b) budding
                              c) fragmentation
                              d) by formation of exospore
  
  
         2. Sexual Reproduction:
                               a) Conjugation
                               b) Transformation
                               c) Transduction
  
  
  
  

  
  

  Bacterial multiplication by transverse binary fission: Asexual reproduction

  
  
  Most bacteria multiply by the process of asexual reproduction. Thus new cells arise from just one parent cell.
  
  
  Process of Binary fission:  In most unicellular prokaryotes the mode of asexual reproduction is ‘Transverse binary fission’ in which each cell divides into two identical daughter cells.
  Prior to cell division the cell contents roughly double in amount and the nucleoid is replicated.
  As the parent cell enlarges, the cytoplasmic membrane extends and the nuclear material becomes separated.
  Cell division occurs in the zone between the two nucleoid, as the membrane near the centre of the enlarged cell pinches outward
  At the same time , new cell wall material grows inward to form a cross wall between the two daughter cells. Daughter cells may separate completely, but in some species they remain attached to form characteristic pairs, clusters, or chains.

  Other asexual mode of reproduction:

  Budding: Some bacteria reproduce by budding, a process in which a small protuberance grows out at one end of the cell. This bud enlarges, eventually becoming a new cell with all cellular constituents and then separating from the parent. 
  Fragmentation: Bacteria that produce filament, reproduce by fragmentation of filaments into small rod shaped or coccoid cells, each of which give rise to new growth.
  Reproduction by exospore formation: Species like Actinomycetes produce chains of exospores called conidia, by developing cross walls at the hyphal tips. Each conidium can develop into a new organism
  

  Conjugation:

  In conjugation one bacterium transfers its genetic material to another bacterium with the help of F pilus and plasmids.
  Plasmids are circular, self-replicating DNAs that are stably maintained in a bacterial cell.
  Donor strains contain an additional genetic element, called the fertility factor or (F). F carried on a plasmid that encodes the transfer machinery. F+ strain mate with F- strains . DNA transfer occurs unidirectionally with the help of F pilus from F+ to the F- (also only a partial transfer).
  After conjugation then each later divides by binary fission.