Chapter 6 : Microbial growth

The requirement for growth ( micro bacterial)

Physical requirements

• temperature pH

• osmotic pressure

Chemical requirements

• carbon

• nitrogen, sulfur, and phosphorous

• trace elements

• oxygen

• organic growth factors

Psychrophiles

loves cold temperatures

optimal temp : 15c or lower

Psychrotrophs

Tolerate

11-12 c

Mesophile

moderate heat ( body temp, tend to be pathogens )

optimal temp : 37C

Thermophiles

heat loving

optimal temp : 62 C

Hyperthermophiles

extreme heat loving

optimal temp : 95C and above

Neutophiles

most bacteria - grow best between pH 6.5 and 7.5

molds and yeast grow

between pH 5 and 6

Acidophiles

grow in acidic environment ( because they like acid they will fight to maintain that pH by creating their own )

Alkaliphiles

grow best in alkaline soils and water

( similar to acidophiles create their own base to maintain their environment )

plasmolysis

causes by hypertonic environments

Obligate halophiles

require high salt concentration

Facultative Halophiles

tolerate high sat concentrations ( but don’t require it )

Carbon

structural backbone of organic molecules

Chemoheterotrophs use organic molecules as both carbon and energy sources

Nitrogen

component of proteins, DNA, and ATP

most bacteria decompose protein-containing material for the nitrogen source )

obligate aerobes

require oxygen

Facultative anaerobes

able to grow with or with oxygen ; grow via fermentation or anaerobic respiration when oxygen is not available ( but do prefer oxygen because it makes more energy )

anaerobes

unable to use oxygen and most are harmed by it ( oxygen can be toxic to microbes that don’t have defense for it )

Aerotolerant anaerobes

tolerate but cannot use oxygen

Microgerophiles

require oxygen concentration lower than air ( will die in the atmosphere)

obligate Aerobes

effect: only aerobic growth; oxygen required

explanation : Presence of enzymes catalase and superoxide dismutase ( SOD) allows toxic forms of oxygen to be neutralized; can use oxygen

Facultative Anaerobes

Effects: both aerobic and anaerobic growth ; greater growth in presence of oxygen

explanation : presence of enzymes catalase and SOD allows toxic forms of oxygen to be neutralized ; can use oxygen

obligate anaerobes

effects : only anaerobic growth ; growth ceases in presence of oxygen

explanation : lacks enzymes to neutralize harmful forms of oxygen ; cannot tolerate oxygen

aerotolerant Anaerobes

effects: only anaerobic growth; but growth continues in the presence of oxygen

explanation : presence of one enzyme, SOD, allows harmful forms of oxygen to be partially neutralized ; tolerates oxygen

Microaerophiles

effects : only aerobic growth ; oxygen required in low concentration

Explanation : Produce lethal amounts of toxic forms of oxygen if exposed to normal atmospheric oxygen

superoxide radicals

( O₂ ^- ) - highlt reactive ( toxic oxygen )

Superoxide dismutase ( SOD)

0_{2 +} O₂ + 2 H⁺ ——> H₂O₂ + O_{2 ( toxic oxygen )}

Peroxide anion

(O₂ ^2- ) - the active component of hydrogen peroxide and benzoyl peroxide

Catalase

H₂ O₂ ——> 2H₂O + O₂

Biofilms

microbial communities ; encased in extreacellular polysaccharides matrix ( EPS )

• form slime or hydrogels that adheare to surfaces

• communicate via quorum sensing

• Share nutrients

• shelter bacteria from harmful environmental factors environmental

• where conjugation & transformation happens

Quorum sensing

bacterial communication to control gene expression based on the number of individuals in a population

autoinducer

used in quorum sensing

secreted chemical molecule used to communicate

• produced constitutively

• Accumulated at high concentration when cell density high

• diffuses into and out of cell

• turn on / off gene expression when concentration high

Binary fission

main mode of how bacteria divides

growth in bacteria is represented in number rather than size the

cell elongates and DNA is replicated

Binary fission step 1

Plasma membrane begins to constrict and new wall is made

binary fission ( step 2 )

cross-wall forms, completely separating the two DNA copies

Binary fission ( step 3 )

cell separate

Binary fission ( step 4 )

time required for a cell to divide

20 min to 24 hours

total number of cells =

2^{the number of generations}

lag Phase

intense activity preparing for population growth, but no increase in population

Log phase

Logarithmic, or exponential, increase in population

Stationary phase

period of equilibrium; microbial deaths balance production of new cells

death phase

population is decreasing at a logarithmic rate