BlackChapter6Growtha
dCulturi
gofBacteria
GROWTHANDCELLDIVISIONMicrobialGrowthDefi
edMicrobialgrowthca
bedefi
edastheorderlyi
creasei
qua
tityofacellcompo
e
tsa
di
the
umberofcellsofa
orga
ismCellDivisio
Mostcelldivisio
i
bacteriaoccurbybi
aryfissio
i
whichthe
uclearbodydividesa
dthecellformsatra
sverseseptumthatseparatestheorigi
alcelli
totwocellsDoubli
gtimeistheperiodrequiredforcellsi
amicrobialpopulatio
togrowdividea
dproducetwo
ewcellsforeacho
ethatexistedbeforeGrowthrateisusuallymeasuredasdoubli
gtimesperhourThetotal
umberofbacteriais2
ishowma
ytimesthebacteriahasdoubledI
completeseparatio
ofthecellsproducesli
earchai
sli
kedbacillitetradsfourcoccisarci
aegroupsofeighti
acubicalpacketorgrapelikeclustersstaphylococciYeatscellsa
dsomebacteriadividebybuddi
gi
whichasmall
ewcelldevelopsfromthesurfaceofa
existi
gcellPhasesofGrowthI
a
utrie
trichmediumamixtureofsubsta
ceso
ori
whichmicroorga
ismsgrowbacteriadividerapidlyThele
gthoftimerequiredforo
edivisio
iscalledthege
eratio
timeSuchgrowthissaidtooccurata
expo
e
tialorlogarithmicrateBacteriai
troducedi
toafresh
utrie
trichmediumdisplayfourmajorphasesofgrowth1I
thelagphasetheorga
ismsaremetabolicallyactivegrowi
ga
dsy
thesizi
gvarioussubsta
cesbut
oti
creasi
gi
umber2I
thelogphaseorga
ismsdivideata
expo
e
tialorlogarithmicratea
dwithaco
sta
tge
eratio
timeUsuallyis20mi
uteswith120ofthecellsdividi
geachmi
ute
o
sy
chro
ousgrowthTheformulaisN2
whereNisthe
umberofcellsi
thecultureafter
doubli
gtimeshavepassedThesepropertiesofgrowthi
thelogphaseca
beusedtocalculateboththe
umberofge
eratio
sa
dthege
eratio
timeCulturesca
bemai
tai
edbytheuseofachemostatwhichallowsco
ti
uousadditio
offreshmedium3I
thestatio
aryphasethe
umberof
ewcellsproducedequalsthe
umberofcelldyi
gThemediumco
tai
slimitedamou
tsof
utrie
tsa
dmayco
tai
toxicqua
tiesofwastematerials4I
thedecli
ephaseordeathphasema
ycellslosetheirabilitytodividea
deve
tuallydieAlogarithmicdecreasei
the
umberofcellsresults
fGrowthi
colo
iesparallelsthati
liquidmediumexceptthatmostgrowthoccursattheedgeofthecolo
ya
dallphasesofgrowthoccursimulta
eouslysomewherei
thecolo
yDeathusuallyoccursbecauseacellhasdepleteditsi
tracellularreserveofATPMeasuri
gBacterialGrowthSomemethodsmeasurecellmassOthersmeasurecell
umbersDetermi
i
gdryweightdepe
dso
separati
gcellsfromtheirmediumdryi
gthema
dweighi
gthem1Growthca
bemeasuredbyserialdilutio
i
whichsuccessive110dilutio
sofaliquidcultureofbacteriar