Presentation 1 - Ex 5

EXERCISE 5 • To set-up conditions to test the influence on microbes of some factors like pH, light, temperature, radiation, salts • To describe effects of these factors on the growth of microbes and explain the physiology involved

ENVIRONMENTAL FACTORS AFFECTING GROWTH

EFFECT OF pH • ACIDITY • ALKALINITY • MICROBIAL GROUPS – ACIDOPHILES • FUNGI, Thiobacillus – ALKALIPHILES • BACILLUS SPECIES • MAY ALSO BE HALOPHILIC – NEUTROPHILES • OPTIMAL BETWEEN pH 6-8

EFFECT OF TEMPERATURE • ONE OF THE MOST IMPROTANT ENVIRONMENTAL FACTORS • MAY GROW FASTER OR CELL COMPONENTS DAMAGED • RANGES OR CARDINAL TEMPERATURES – MINIMUM – MAXIMUM – OPTIMUM

CLASSES OF ORGANISMS BASED ON TEMPERATURE • PSYCHROTOLERANT – WIDE DISTRIBUTION

• PSYCHROPHILES – Flavobacterium species

• MESOPHILES – E. coli

• THERMOPHILES – Bacillus strearothermophilus

• HYPERTHERMOPHILES – Thermococcus celer

PHYSIOLOGY • PSYCHROPHILY – HIGH CONTENT OF UNSATURATED FATTY ACIDS – HELP MAINTAIN A SEMI-FLUID MEMBRANE STATE AT LOW TEMPERATURE

• THERMOPHILY – PROTEINS OR ENZYMES = INCREASED NUMBER OF SALT BRIDGES (RESIST UNFOLDING IN THE AQUEOUS MILIEU) – MEMBRANES = RICH IN SATURATED FATTY ACIDS (STABLE AT HIGH TEMPERATURES)

WATER AVAILABILITY • WATER = SOLVENT OF LIFE • WATER AVAILABILITY = IMPORTANT FACTOR AFFECTING GROWTH • WATER ACTIVITY AND OSMOSIS

WATER ACTIVITY AND OSMOSIS •

MICROBIAL GROUPS BASED ON WATER ACTIVITY/OSMOTIC EFFECTS – HALOPHILES • SPECIFIC REQUIREMENT FOR SODIUM ION (1-6%) • Vibrio fischeri

– HALOTOLERANT • CAN TOLERATE REDUCTION IN WATER ACTIVITY • BUT GENERALLY GROW BEST IN THE ABSENCE OF THE ADDED SOLUTE • Staphylococcus aureus

– EXTREME HALOPHILES • GROWTH IN VERY SALTY ENVIRONMENTS (15-20% NaCl) • Halococcus, Halobacterium

– OSMOPHILES • GROWTH IN ENVIRONMENTS OF HIGH SUGAR • Gram positive cocci

– XEROPHILES • GROW IN VERY DRY ENVIRONMENTS • Xeromyces bisporus

EFFECT OF OXYGEN • MICROBIAL GROUPS BASED ON OXYGEN REQUIREMENTS • PHYSIOLOGY OF OXYGEN TOLERANCE • TOXIC FORMS AND ENZYMES THAT DESTROY TOXIC OXYGEN – TRIPLET (Normal ground state) TO SINGLET (major form of toxif oxygen) OXYGEN – Carotenoids = convert singlet oxygen to non-toxic forms – Catalase = for toc oxygen derivatives such as hydrogen peroxide

EFFECT OF ALCOHOL • DISINFECTANTS – DECONTAMINATE OR STERILIZE INANIMATE OBJECTS

• ANTISEPTICS – DECONTAMINATE LIVING TISSUES

• WHY 70% ALCOHOL?

EFFECT OF RADIATION • IONIZING – TARGETS DNA MOLECULES – CHEMICAL CHANGES IN ORGANELLE – GAMMA RAYS, X-RAYS, CATHODE RAYS

• NON-IONIZING – EXCITES ATOM BY RAISING THEM TO A HIGHER ENERGY STATE – DOES NOT IONIZE – LEADS TO ABNORMAL LINKAGES WITHIN DNA MOLECULES – MUTATION – UV LIGHT

CELLULAR EFFECTS OF RADIATION • IONIZING – CAN PENETRATE A SOLID BARRIER, BOMBARD A CELL, ENTER IT AND DISLODGE ELECTRONS FROM MOLECULES – BEAKAGE OF DNA CREATES MASSIVE MUTATION

• NON-IONIZING – ENTERS A CELL, STRIKES OLECULES AND EXCITES THEM – MUTATION ON DNA BY FORMATION OF ABNORMAL BONDS – A SOLID BARRIER CANNOT BE PENETRATED BY A NON-IONIZING RADIATION