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Th e Gr ow t h of Ba ct e r ia l Popu la t ion s ( pa ge 1 )
Microbiological Equipment ( This chapt er has 4 pages) Choose NuAire For All Your
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M e a su r e m e n t of Ba ct e r ia l Gr ow t h
www. NuAire.com /CellCultureEquipmentscaffolding Gr ow t h is an orderly increase in t he quant it y of cellular const it uent s . I t depends upon
t he abilit y of t he cell t o form new prot oplasm from nut rient s available in t he
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environm ent . I n m ost bact eria, grow t h involves increase in cell m ass and num ber of
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ribosom es , duplicat ion of t he bact erial chrom osom e, synt hesis of new cell wall and
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plasm a m em brane , part it ioning of t he t wo chrom osom es, sept um form at ion , and cell
www. qingdao-scaffolding. com division . This asexual process of reproduct ion is called bin a r y fission .
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www. SonyEricsson.com Web Review of Todar's Online Text book of Bact eriology. "The Good , t he Bad , and t he
Deadly" . (SCI ENCE Magazine- June 4 , 2004 - Vol 304 : p. 1421 ).
Tag w ords : bact erial growt h , growt h curve, lag phase, exponent ial growt h , generat ion t im e, viable cell count, cont inuous cult ure.
Figu r e 1 . Ba ct e r ia l gr ow t h by bin a r y fission . M ost ba ct e r ia r e pr odu ce by a r e la t ive ly sim ple a se x u a l pr oce ss ca lle d bin a r y fission: e a ch ce ll in cr e a se s in Ads by Google siz e a n d divide s in t o t w o ce lls. D u r in g t h is pr oce ss t h e r e is a n or de r ly in cr e a se Cell in ce llu la r st r u ct u r e s a n d com pon e n t s, r e plica t ion a n d se gr e ga t ion of t h e ba ct e r ia l D N A , a n d for m a t ion of a se pt u m or cr oss w a ll w h ich divide s t h e ce ll
Bacteria in t o t w o pr oge n y ce lls Th e pr oce ss is coor din a t e d by t h e ba ct e r ia l m e m br a n e
Culture Growth pe r h a ps by m e a n s of m e sosom e s . Th e D N A m ole cu le is be lie ve d t o be a t t a ch e d
t o a poin t on t h e m e m br a n e w h e r e it is r e plica t e d . Th e t w o D N A m ole cu le s r e m a in a t t a ch e d a t poin t s side- by - side on t h e m e m br a n e w h ile n e w m e m br a n e m a t e r ia l is syn t h e siz e d be t w e e n t h e t w o poin t s. Th is dr a w s t h e D N A m ole cu le s in opposit e dir e ct ion s w h ile n e w ce ll w a ll a n d m e m br a n e a r e la id dow n a s a se pt u m be t w e e n t h e t w o ch r om osom a l com pa r t m e n t s . W h e n se pt u m for m a t ion is com ple t e t h e ce ll split s in t o t w o pr oge n y ce lls. Th e t im e in t e r va l r e qu ir e d for a ba ct e r ia l ce ll t o divide or for a popu la t ion of ba ct e r ia l ce lls t o dou ble is ca lle d t h e ge n e r a t ion t im e. Ge n e r a t ion t im e s for ba ct e r ia l spe cie s gr ow in g in n a t u r e m a y be a s sh or t a s 1 5 m in u t e s or a s lon g a s se ve r a l da ys. Ele ct r on m icr ogr a ph of St r e pt ococcu s pyoge n e s by M a r ia Fa z io a n d V in ce n t A. Fisch e t t i , Ph . D . w it h pe r m ission . Th e La bor a t or y of Ba ct e r ia l Pa t h oge n e sis a n d I m m u n ology , Rock e fe lle r Un ive r sit y .For unicellular organism s such as t he bact eria, growt h can be m easured in t erm s of t wo different param et ers: changes in ce ll m a ss and changes in ce ll n u m be r s .
M e t h ods for M e a su r e m e n t of Ce ll M a ss
Met hods for m easurem ent of t he cell m ass involve bot h direct and indirect t echniques . 1 . Direct ph ysica l m e a su r e m e n t of dry weight , wet weight , or volum e of cells aft er cent rifugat ion .
2 . Direct ch e m ica l m e a su r e m e n t of som e chem ical com ponent of t he cells such as t ot al N, t ot al prot ein , or t ot al DNA cont ent . 3 . I ndirect
m e a su r e m e n t of ch e m ica l a ct ivit y such as rat e of O2 production or consum pt ion , CO product ion or consum pt ion , et c.
2 4 . Tu r bidit y m e a su r e m e n t s em ploy a variet y of inst rum ent s t o det erm ine t he am ount of light scat t ered by a suspension of cells. Part iculat e obj ect s such as bact eria scat t er light in proport ion t o t heir num bers . The t urbidit y or opt ica l de n sit y of a suspension of cells is direct ly relat ed t o cell m ass or cell num ber, aft er const ruct ion and calibrat ion of a st andard curve . The m et hod is sim ple and nondest ruct ive , but t he sensit ivit y is lim it ed t o about 10 7 cells per m l for m ost bacteria.
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Th e Gr ow t h of Ba ct e r ia l Popu la t ion s ( pa ge 2 )
Met hod Applicat ion Com m ent s Direct m icroscopic count
Measurem ent of t ot al cell yield in cult ures probably m ore sensit ive t han t ot al N or t ot al prot ein m easurem ent s
Measurem ent of dry weight or w et w eight of cells or volum e of cells aft er cent rifugat ion
Microbiological assays Requires a fixed st andard t o relat e chem ical act ivit y t o cell m ass and/ or cell num bers
Measurem ent of Biochem ical act ivit y e. g. O2 upt ake CO2 product ion , ATP product ion , et c.
Measurem ent of t ot al cell yield from very dense cult ures only pract ical applicat ion is in t he research laborat ory
7 cells per m l Measurem ent of t ot al N or prot ein
Fast and nondest ruct ive , but cannot det ect cell densit ies less t han 10
Est im at ions of large num bers of bact eria in clear liquid m edia and brot hs
Very sensit ive if plat ing condit ions are opt im al Turbidit y m easurem ent
Viable cell count ( colony count s) Enum erat ion of bact eria in m ilk , foods , soil , wat er , laborat ory cult ures, et c.
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Ta ble 1 . Som e M e t h ods u se d t o m e a su r e ba ct e r ia l gr ow t h
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Measuring t echniques involve direct count s, visually or inst rum ent ally , and indirect viable cell count s. 1 . D ir e ct m icr oscopic cou n t s are possible using special slides known as count ing cham bers. Dead cells cannot be dist inguished from living ones. Only dense suspensions can be count ed ( > 10 7 cells per m l) , but sam ples can be concentrated by centrifugation or filt rat ion t o increase sensit ivit y. A variat ion of t he direct m icroscopic count has been used t o observe and m easure grow t h of bact eria in nat ural environm ent s. I n order t o det ect and prove t hat t herm ophilic bact eria w ere grow ing in boiling hot springs , T . D . Brock im m ersed m icroscope slides in t he springs and wit hdrew t hem periodically for m icroscopic observat ion. The bact eria in t he boiling wat er at t ached t o t he glass slides nat urally and grew as m icrocolonies on t he surface . 2 . Ele ct r on ic cou n t in g ch a m be r s count num bers and m easure size dist ribut ion of cells. For cells t he size of bact eria t he suspending m edium m ust be very clean. Such elect ronic devices are m ore oft en used t o count eucaryot ic cells such as blood cells. 3 . I n dir e ct via ble ce ll cou n t s, also called pla t e cou n t s, involve plat ing out ( spreading) a sam ple of a cult ure on a nut rient agar surface . The sam ple or cell suspension can be dilut ed in a nont oxic diluent ( e. g . wat er or saline) before plat ing. I f plat ed on a suit able m edium , each viable unit grow s and form s a colony . Each colony t hat can be count ed is called a colon y for m in g u n it ( cfu ) and t he num ber of cfu' s is relat ed t o t he viable num ber of bact eria in t he sam ple . Advant ages of t he t echnique are it s sensit ivit y ( t heoret ically , a single cell can be det ect ed ) , and it allows for inspect ion and posit ive ident ificat ion of t he organism count ed. Disadvant ages are ( 1 ) only living cells develop colonies t hat are count ed; ( 2 ) clum ps or chains of cells develop int o a single colony ; ( 3 ) colonies develop only from t hose organism s for which t he cult ural condit ions are suit able for grow t h. The lat t er m akes t he t echnique virt ually useless t o charact erize or count t he t ot a l n u m be r of ba ct e r ia in com plex m icrobial ecosyst em s such as soil or t he anim al rum en or gast roint est inal t ract . Genet ic probes can be used t o dem onst rat e t he diversit y and relat ive abundance of procaryot es in such an environm ent , but m any species ident ified by genet ic t echniques have so far proven uncult urable.
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Web Review of Todar' s Online Text book of Bact eriology. "The Good, t he Bad, and t he
Deadly" . (SCI ENCE Magazine - June 4 , 2004 - Vol 304 : p. 1421 ).
Tag w ords: bact erial grow t h , grow t h curve, lag phase , exponent ial growt h , generat ion t im e, viable cell count, cont inuous cult ure.
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M e t h ods for M e a su r e m e n t of Ce ll N u m be r s
En doLI SA® En dot ox in Te st
Enum erat ion of bact eria in m ilk or cellular vaccines Cannot dist inguish living from nonliving cells
Figu r e 2 . Ba ct e r ia l colon ie s gr ow in g on a pla t e of n u t r ie n t a ga r. H a n s Kn oll I n st it u t e. Je n a , Ge r m a n y . Sk ill D e ve lopm e n t Cou r se s
Develop Leadership Skills For Great er Success. Find Out More ! w ww . ccl . org chapt er cont inued Previous Page © Kennet h Todar, Ph . D . All right s reserved . - w w w . t ext bookofbact eriology. net
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Th e Gr ow t h of Ba ct e r ia l Popu la t ion s ( pa ge 3 )
( This chapt er has 4 pages) © 2011 Kennet h Todar, PhD Th e Ba ct e r ia l Gr ow t h Cu r ve
I n t he laborat ory, under favorable condit ions, a grow ing bact erial populat ion doubles at
1
2 regular int ervals. Growt h is by geom et ric progression: 1 , 2 , 4 , 8 , et c. or 2 , 2 , 2 ,
Feat ured Microbe 2 3 .. ..... ..2 n ( where n = the num ber of generations) . This is called exponential grow th.
I n realit y, exponent ial growt h is only part of t he bact erial life cycle, and not
Microbiological Equipment represent at ive of t he norm al pat t ern of grow t h of bact eria in Nat ure.
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When a fresh m edium is inoculat ed wit h a given num ber of cells, and t he populat ion
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grow t h is m onit ored over a period of t im e, plot t ing t he dat a w ill yield a t ypica l ba ct e r ia l
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Web Review of Todar' s Online Text book of Bact eriology. "The Good, t he Bad, and t he
Deadly" . (SCI ENCE Magazine - June 4 , 2004 - Vol 304 : p. 1421 ).
Tag w ords: bact erial grow t h , grow t h Figu r e 3 . Th e t ypica l ba ct e r ia l gr ow t h cu r ve . W h e n ba ct e r ia a r e gr ow n in a curve, lag phase , exponent ial growt h , close d syst e m ( a lso ca lle d a ba t ch cu lt u r e ) , lik e a t e st t u be, t h e popu la t ion of generat ion t im e, viable cell count, cont inuous cult ure. ce lls a lm ost a lw a ys e x h ibit s t h e se gr ow t h dyn a m ics : ce lls in it ia lly a dj u st t o t h e n e w m e diu m ( la g ph a se ) u n t il t h e y ca n st a r t dividin g r e gu la r ly by t h e pr oce ss of bin a r y fission ( e x pon e n t ia l ph a se ) . W h e n t h e ir gr ow t h be com e s lim it e d, t h e ce lls st op dividin g ( st a t ion a r y ph a se ) , u n t il e ve n t u a lly t h e y sh ow loss of via bilit y Ads by Google ( de a t h ph a se ) . N ot e t h e pa r a m e t e r s of t h e x a n d y a x e s . Gr ow t h is e x pr e sse d
Cell Culture a s ch a n ge in t h e n u m be r via ble ce lls vs t im e. Ge n e r a t ion t im e s a r e ca lcu la t e d du r in g t h e e x pon e n t ia l ph a se of gr ow t h. Tim e m e a su r e m e n t s a r e in h ou r s for
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ba ct e r ia w it h sh or t ge n e r a t ion t im e s .
Culture Growth Four charact erist ic phases of t he grow t h cycle are recognized
1 . La g Ph a se . I m m ediat ely aft er inoculat ion of t he cells int o fresh m edium , t he populat ion rem ains t em porarily unchanged. Alt hough t here is no apparent cell division occurring , t he cells m ay be grow ing in volum e or m ass, synt hesizing enzym es, prot eins, RNA , et c. , and increasing in m et abolic act ivit y.
The lengt h of t he lag phase is apparent ly dependent on a wide variet y of fact ors including t he size of t he inoculum; t im e necessary t o recover from physical dam age or shock in t he t ransfer ; t im e required for synt hesis of essent ial coenzym es or division fact ors ; and t im e required for synt hesis of new ( inducible) enzym es t hat are necessary t o m et abolize t he subst rat es present in t he m edium . 2 . Ex pon e n t ia l ( log ) Ph a se . The exponent ial phase of growt h is a pat t ern of balanced grow t h w herein all t he cells are dividing regularly by binary fission, and are grow ing by geom et ric progression. The cells divide at a const ant rat e depending upon t he com posit ion of t he grow t h m edium and t he condit ions of incubat ion . The rat e of exponent ial grow t h of a bact erial cult ure is expressed as ge n e r a t ion t im e, also t he dou blin g t im e of t he bact erial populat ion. Generat ion t im e ( G ) is defined as t he t im e ( t ) per generat ion ( n = num ber of generat ions) . Hence , G = t / n is t he equat ion from which calculat ions of generat ion t im e ( below) derive .
3 . St a t ion a r y Ph a se . Exponent ial growt h cannot be cont inued forever in a ba t ch
cu lt u r e ( e . g . a closed syst em such as a t est t ube or flask ) . Populat ion growt h is lim it ed
by one of t hree fact ors : 1 . exhaust ion of available nut rient s; 2 . accum ulat ion of inhibit ory m et abolit es or end product s; 3 . exhaust ion of space, in t his case called a lack of
During t he st at ionary phase, if viable cells are being count ed, it cannot be det erm ined w het her som e cells are dying and an equal num ber of cells are dividing , or t he populat ion of cells has sim ply st opped grow ing and dividing. The st at ionary phase, like t he lag phase, is not necessarily a period of quiescence. Bact eria t hat produce se con da r y m e t a bolit e s, such as ant ibiot ics , do so during t he st at ionary phase of t he grow t h cycle ( Secondary m et abolit es are defined as m et abolit es produced aft er t he act ive st age of grow t h) . I t is during t he st at ionary phase t hat spore- form ing bact eria have t o induce or unm ask t he act ivit y of dozens of genes t hat m ay be involved in sporulat ion process.
4 . D e a t h Ph a se . I f incubat ion cont inues aft er t he populat ion reaches st at ionary phase, a deat h phase follow s, in which t he viable cell populat ion declines. ( Not e, if count ing by t urbidim et ric m easurem ent s or m icroscopic count s, t he deat h phase cannot be observed . ) . During t he deat h phase, t he num ber of viable cells decreases geom et rically ( exponent ially ) , essent ially t he reverse of grow t h during t he log phase.
Gr ow t h Ra t e a n d Ge n e r a t ion Tim e
As m ent ioned above, bact erial grow t h rat es during t he phase of exponent ial grow t h, under st andard nut rit ional condit ions ( cult ure m edium , t em perat ure , pH, et c. ) , define t he bact erium 's generat ion t im e. Generat ion t im es for bact eria vary from about 12 m inut es t o 24 hours or m ore . The generat ion t im e for E. coli in t he laborat ory is 15 - 20 m inut es, but in t he int est inal t ract , t he coliform ' s generat ion t im e is est im at ed t o be 12- 24 hours. For m ost known bact eria t hat can be cult ured , generat ion t im es range from about 15 m inut es t o 1 hour . Sym biont s such as Rhizobium t end t o have longer generat ion t im es . Many lit hot rophs, such as t he nit rifying bact eria, also have long generat ion t im es. Som e bact eria t hat are pat hogens , such as Mycobact erium t uberculosis and Treponem a
pallidum , have especially long generat ion t im es, and t his is t hought t o be an advant age in
t heir virulence. Generat ion t im es for a few bact eria are are shown in Table 2.
Ta ble 2 . Ge n e r a t ion t im e s for som e com m on ba ct e r ia u n de r opt im a l con dit ion s
of gr ow t h.
Ba ct e r iu m M e diu m Ge n e r a t ion Tim e ( m in u t e s)
Escherichia coli Glucose - salt s17 Bacillus m egat erium Sucrose- salt s
25 St rept ococcus lact is Milk
26 St rept ococcus lact is Lact ose brot h
48 St aphylococcus aureus Heart infusion brot h 27- 30
Lact obacillus acidophilus Milk 66- 87 Rhizobium j aponicum Mannit ol- salt s - yeast ext ract 344- 461
Mycobact erium t uberculosis Synt het ic 792- 932 Rabbit t est es 1980
Treponem a pallidum Ca lcu la t ion of Ge n e r a t ion Tim e
When grow ing exponent ially by binary fission, t he increase in a bact erial populat ion is by geom et ric progression. I f w e st art wit h one cell , when it divides, t here are 2 cells in t he first generat ion, 4 cells in t he second generat ion, 8 cells in t he t hird generat ion, and so on. The ge n e r a t ion t im e is t he t im e int erval required for t he cells ( or populat ion) t o divide. G ( generat ion t im e) = ( t im e, in m inut es or hours) / n( num ber of generat ions) G = t / n t = t im e int erval in hours or m inut es B = num ber of bact eria at t he beginning of a t im e int erval b = num ber of bact eria at t he end of t he t im e int erval n = num ber of generat ions ( num ber of t im es t he cell populat ion doubles during t he t im e int erval) b = B x 2 n ( This equation is an expression of growth by binary fission ) Solve for n : logb = logB + nlog 2 n = logb - logB log2 n = logb - logB . 301 n = 3 . 3 logb/ B G = t / n Solve for G G = t 3 . 3 log b / B
Ex a m ple: W h a t is t h e ge n e r a t ion t im e of a ba ct e r ia l popu la t ion t h a t in cr e a se s fr om 1 0 , 0 0 0 ce lls t o 1 0 , 0 0 0 , 0 0 0 ce lls in fou r h ou r s of gr ow t h?
G = t _____ 3 . 3 log b / B G = 240 m inut es 3 . 3 log 10
7 / 10 4 G = 240 m inut es 3 . 3 x 3 G = 24 m inut es
Gr ow 3 d ce ll cu lt u r e s
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Th e Gr ow t h of Ba ct e r ia l Popu la t ion s ( pa ge 4 )
( This chapt er has 4 pages) © 2011 Kennet h Todar, PhD Con t in u ou s Cu lt u r e of Ba ct e r ia
The cult ures so far discussed for grow t h of bact erial populat ions are called ba t ch
cu lt u r e s. Since t he nut rient s are not renewed, exponent ial growt h is lim it ed t o a few Feat ured Microbe
generat ions. Bact erial cult ures can be m aint ained in a st at e of exponent ial grow t h over long periods of t im e using a syst em of con t in u ou s cu lt u r e ( Figure 4 ) , designed t o relieve t he condit ions t hat st op exponent ial grow t h in bat ch cult ures. Cont inuous cult ure,
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in a device called a ch e m ost a t , can be used t o m aint ain a bact erial populat ion at a
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const ant densit y , a sit uat ion t hat is, in m any ways, m ore sim ilar t o bact erial grow t h in
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I n a chem ost at , t he grow t h cham ber is connect ed t o a reservoir of st erile m edium . Once grow t h is init iat ed, fresh m edium is cont inuously supplied from t he reservoir . The volum e
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grow t h of t he bact eria. The bact eria grow ( cells are form ed ) at t he sam e rat e t hat
from matrix effects
bact erial cells ( and spent m edium ) are rem oved by t he overflow. The rat e of addit ion of
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t he fresh m edium det erm ines t he rat e of grow t h because t he fresh m edium always cont ains a lim it ing am ount of an essent ial nut rient . Thus, t he chem ost at relieves t he insufficiency of nut rient s, t he accum ulat ion of t oxic subst ances, and t he accum ulat ion of
Web Review of Todar' s Online Text book of excess cells in t he cult ure, which are t he param et ers t hat init iat e t he st at ionary phase of Bact eriology. "The Good, t he Bad, and t he
Deadly" . (SCI ENCE Magazine - June 4 ,
t he growt h cycle. The bact erial cult ure can be grown and m aint ained at relat ively 2004 - Vol 304 : p. 1421 ). const ant condit ions , depending on t he flow rat e of t he nut rient s.
Tag w ords: bact erial grow t h , grow t h curve, lag phase , exponent ial growt h , generat ion t im e, viable cell count, cont inuous cult ure.
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Figu r e 4 . Sch e m a t ic dia gr a m of a ch e m ost a t , a de vice for t h e con t in u ou s cu lt u r e of ba ct e r ia . Th e ch e m ost a t r e lie ve s t h e e n vir on m e n t a l con dit ion s t h a t r e st r ict gr ow t h by con t in u ou sly su pplyin g n u t r ie n t s t o ce lls a n d r e m ovin g w a st e su bst a n ce s a n d spe n t ce lls fr om t h e cu lt u r e m e diu m . Syn ch r on ou s Gr ow t h of Ba ct e r ia
St udying t he grow t h of bact erial populat ions in bat ch or cont inuous cult ures does not perm it any conclusions about t he grow t h behavior of individual cells, because t he dist ribut ion of cell size ( and hence cell age) am ong t he m em bers of t he populat ion is com plet ely random . I nform at ion about t he growt h behavior of individual bact eria can, how ever, be obt ained by t he st udy of syn ch r on ou s cu lt u r e s. Synchronized cult ures m ust be com posed of cells which are all at t he sam e st age of t he ba ct e r ia l ce ll cycle . Measurem ent s m ade on synchronized cult ures are equivalent t o m easurem ent s m ade on individual cells.
A num ber of clever t echniques have been devised t o obt ain bact erial populat ions at t he sam e st age in t he cell cycle. Som e t echniques involve m anipulat ion of environm ent al param et ers which induces t he populat ion t o st art or st op grow t h at t he sam e point in t he cell cycle, while ot hers are physical m et hods for select ion of cells t hat have j ust com plet ed t he process of binary fission. Theoret ically, t he sm allest cells in a bact erial rapidly lose synchrony because not all cells in t he populat ion divide at exact ly t he sam e size, age or t im e .
Figu r e 5 . Th e syn ch r on ou s gr ow t h of a ba ct e r ia l popu la t ion . By ca r e fu l se le ct ion of ce lls t h a t h a ve j u st divide d , a ba ct e r ia l popu la t ion ca n be syn ch r on iz e d in t h e ba ct e r ia l ce ll division cycle . Syn ch r on y ca n be m a in t a in e d for on ly a fe w ge n e r a t ion s. Sk ill D e ve lopm e n t Cou r se s
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