Infective cycle of dairy bacteriophages

GUGLIELMOTTI, D.M.; MERCANTI, D.J.; BRIGGILER MARCÓ, M.

Bacteriophages in Dairy Processing

NOVA Publishers

Lugar: New York; Año: 2012; p. 99 - 122

Phages follow  two strategies to survive: they can either infect and lyse the host cell (virulent/lytic  phages)  or  insert  its  genome  into  the  host  chromosome  (prophages).  In either  case,  the  first  step  is  the  adsorption  of  virions  to  specific  attachment  sites (receptors)  on  the  cell wall  surface. Adsorption  velocity  and  efficiency  depend  upon  a series of external  factors, such as  the presence of divalent  ions  (Ca2+, Mg2+, Mn2+), pH, temperature, inorganic salts, and the physiological state of bacterial cells. In general, both divalent cations and physiological state of the host show little or no influence on the rate of  adsorption,  whereas maximum  adsorption  is  in  general  attained  at  the  optimal  cell growth  temperature and pH close  to neutrality. Adsorption  interference  is  regarded as a significant  mechanism  of  phage  resistance  in  lactic  acid  bacteria  (LAB),  and  thus research  on  this  topic  is  very  valuable.  These  studies  are  directed  to  characterize  the chemical  nature  of  phage  receptors  and  encompass  the  use  of  diverse  chemical compounds and enzymes. When  receptors are carbohydrate  in nature,  the use of  lectins and either simple or complex saccharides in competition and desorption assays could be very  useful.  Injection  of  phage  DNA  into  the  cytoplasm  comes  after  irreversible attachment step of adsorption. Unlike adsorption,  the DNA  injection process was  found to be highly dependent on Ca2+. Besides, temperature and physiological state of the host had an important influence as well. During the latent phase of a lytic cycle, phage DNA is replicated  and phage genes  are  transcribed  in  strict order. Proteins of  tailed phages  are assembled through separate pathways into heads, tails and fibers. Once phage virions are fully assembled, they must escape from the host cell so as to persist in nature. To do this, lytic phages must degrade or at least compromise the peptidoglycan layer of the cell wall. Likewise  the  rest of  tailed bacteriophages,  those  infecting LAB  lyse  the host using  two phage-encoded  factors:  a  small  hydrophobic  protein  that  permeabilizes  the  membrane (holin), allowing  the second one  (lysin)  to gain access  to  the cell wall. Genes encoding for either holin or lysin were found to be highly conserved among phages infecting LAB.