2.6 Environmental control of metabolism in microorganisms

Question 1

What do microorganisms include?

Answer 1

archaea, bacteria and some species of eukaryote such as yeast and protozoans

Question 2

What kind of species do microorganisms include?

Answer 2

includes species that use a wide range of substrates for metabolism and produce a wide range of products from their metabolic pathway.

Question 3

Benefit of microorganisms?

Answer 3

microorganisms are very adaptable and so can be found in a wide range of ecological niches

Question 4

What are microorganisms used for?

Answer 4

a variety of research and industrial applications cause they reproduce and grow quickly

Question 5

What is the growth of microorganisms influenced by?

Answer 5

the composition of their growth medium and the environmental conditions in which they are being cultured

Question 6

Growth of microorganisms in a lab requires what?

Answer 6

culture (growth) medium

a suitable environment

Question 7

What must microorganisms be provided with?

Answer 7

respiratory substrate in the growth medium (if they cannot use light for photosynthesis) together with ‘building blocks’ for the biosynthesis of proteins and nucleic acids ( a supply of amino acids and nucleotides)

Question 8

What additional compounds must be added to a growth medium?

Answer 8

fatty acids and specific vitamins must be added to the growth medium of certain complex microorganisms in order to culture them in laboratory successfully

Question 9

why is it important to maintain optimum environmental conditions?

Answer 9

produce maximum yield of product

Question 10

Why do culture conditions include sterility?

Answer 10

to eliminate any effects of contaminating microorganisms and the control of temperature (thermostat) oxygen levels (aeration) and pH (buffers or the addition of acid/alkalis)

Question 11

STOP

Answer 11

sterility
temperature
oxygen
pH

Question 12

TOP TIP

Answer 12

bacteria cultured on agar plates require oxygen so the plates must not be sealed completely

Question 13

What are industrial fermenters?

Answer 13

or bioreactors which are used to culture microorganisms on a huge scale, are controlled automatically by computers

Question 14

What do sensors do?

Answer 14

monitor the culture conditions and maintain the factors affecting growth at their optimum level

Question 15

TOP TIP

Answer 15

Microorganisms can be cultured to produce useful secondary metabolites such as penicillin, alcohol and some medicines

Question 16

Define growth?

Answer 16

growth can be defined as the irreversible increase in dry biomass of an organism

growth of unicellular organisms such as bacteria and yeast is recorded by measuring the increase in cell number in a given period of time

Question 17

TOP TIP

Answer 17

the dry mass is more reliable measurement of growth than fresh mass because fresh mass includes water content in the cells of the organisms which can vary independently of growth

Question 18

What are the four phases?

Answer 18

lag phase
log or exponential growth phase
stationary phase
death or logarithmic decline phase

Question 19

Explain Lag phase?

Answer 19

cell numbers, increase very slowly, if at all, during this phase
the cells are preparing for division by synthesising nucleic acids and enzymes
they use the nutrients in the new culture medium in which they have been placed
the length of the lag phase depends on the level of damage or ‘shock’ that cells most recover from and the time required to synthesise new materials

Question 20

Explain Log phase?

Answer 20

exponential growth takes place due to high availability of food and conditions which are optimal
the cells double in number at regular intervals
this constant growth rate is called the generation time (doubling time) and is dependent on both environmental conditions and the species of microbe

Question 21

Explain Stationary phase?

Answer 21

as the cells are no longer in a period of active growth, they start to produce secondary metabolites - molecules not required for cell growth but which may give the cell an ecological advantage
antibiotics such as penicillin are produce as secondary metabolites, inhibiting the growth of other microbes and therefore reducing competition for nutrients
Antibiotics and other secondary metabolites that are of use to humans are produced on an industrial scale using fermenters

Question 22

Explain death phase?

Answer 22

lack of food/ and or oxygen and the build up of toxic metabolites causes an increase in the death rate over the rate of cell production
autolysis of dead cells may release nutrients required for further cell growth

Question 23

What is the total cell count?

Answer 23

the number of cells visible in the field of view

Question 24

What is the viable cell count?

Answer 24

the number of those cells that are actively dividing

Question 25

Drawing graphs of growth rate?

Answer 25

under ideal conditions, cell number and the death rate of population increase doubles at each cell division (exponential growth)
plotting population size against time on a normal graph paper soon becomes unmanageable as cell numbers increase rapidly
an alternative method is to use semi logarithmic graph paper
time is plotted on the x axis with a linear scale as usual
the y axis scale however is not linear
instead the scale is divided into repeating series (cycles) of intervals
in each cycle the cell numbers being plotted are 10 time bigger than in previous cycle
so first cycle is 1-10, second is 10-100, third is 100-1000 and so on

Question 26

DONT FORGET

Answer 26

exponential growth plotted on semi-logarithmic paper takes the form of a straight line

Question 27

How can the metabolism of prokaryotic cells grown in culture be controlled by?

Answer 27

the addition of metabolic precursors, inducers or inhibitors to produce the desired end product

Question 28

FLOW DIAGRAM

control of metabolism

Answer 28

metabolite P —> precursor required so that enzyme 1 can produce metabolite Q
| enzyme 1
metabolite Q —> Induced required to bring about production of enzyme 2
| \ enzyme 2
metabolite R —> desired product
| enzyme 3
metabolite S

Question 29

What is primary metabolism?

Answer 29

refers to the metabolism of a microorganism that occurs during the lag and log phases of growth
this is when it breaks down the available substrate to obtain energy and produce primary metabolites that can be used for the biosynthesis of substances such as proteins and nucleic acids

Question 30

what is secondary metabolism?

Answer 30

occurs at the end of a log phase and during the stationary phase of growth
secondary metabolism produces substances that are not associated with growth but which may confer an ecological advantage
examples - antibiotics which inhibit growth of bacteria