Culturing microorganisms on an industrial scale

Factors to take into account

  • chosen microorganism must be able to produce chosen product

  • Reasonably fast

  • Good yield

  • Uses cheap nutrients

  • Not require extreme conditions

  • Not produce contaminants

  • Not mutate into non functioning forms

Primary metabolites

  • chemicals that are made as direct result of the metabolism of the microorganism and involved in the normal growth of the organism

    • Eg. Enzymes

  • Usually formed during the growth phase

Secondary metabolites

  • chemicals made by the organism but not essential for growth or metabolic processes

    • Antibiotics in moulds

    • Defensive chemicals in plants

  • Usually formed during the stationary phase

Harvesting a primary or secondary metabolite

Types of reactor

  • Batch

    • All nutrients are added at the same time

    • All stages of microbial growth are seen

    • Used for production of secondary metabolites

  • Continuous

    • Nutrients added continually

    • Aim to maintain exponential growth used for production of primary metabolites

Batch reactor

  • Fermenters tend to be relatively large

  • Closed system

  • Less chance contamination

  • Microbes in the fermenter show lag, log, and stationary phases

  • Most suitable for the production of secondary metabolites

  • Nutrients are only added at the beginning

  • Fermenter is washed and sterilised before another batch can be set up

  • Process is stopped once product is formed

Continuous reactor

  • Fermenters tend to be smaller

  • Open system

  • More chance of contamination

  • Most suitable for the production of primary metabolites

  • Optimum or exponential is maintained in the fermenter

  • The process is not stopped for the collection of the product - removed continuously from fermenter

  • Washing and sterilisation is not needed

Control factors in a bioreactor to give max product yield

  • temperature

    • Too low

      • Growth rate too slow

    • Too high

      • Enzymes dentature

    • Temperature sensors and negative feedback heating/cooling system used to maintain optimum conditions

  • Nutrients and oxygen

    • Added as needed to maintain growth as required

    • Probes or sample testing provide information on these levels

  • Mixing things up

    • Continuous stirring ensures all microorganisms receive nutrients and oxygen

    • Also helps maintain a constant temperature

  • Asepsis

    • Contamination by other microorganisms will affect yield

    • Most reactors are sealed units to prevent this

    • Genetically engineered organisms must legally be kept contaminated

Batch reactor producing penicillin

  • Above is a batch reactor as penicillin is a secondary metabolite

  • The sparger introduces gases/oxygen continually

  • It is necessary to circulate cold water through the insulating jacket as heat from respiration could denature enzymes and cold water will maintain optimum temperature