11 Fisiologi Bakteri.pdf

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FISIOLOGI BAKTERI

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Microbial Life in the Cold • The organisms that live in these environments are therefore called Psychrophilic, ex: Polaromonas (have very low growth temperature optima and maxima  4oC and 12oC • A species of the sea ice bacterium Psychromonas grows at 12oC • Adaptation  Produce enzymes that function optimally in the cold and that may be denaturated or otherwise inactivated at even very moderate temperatures  Protein structure

Microbial Life in the Cold • The cytoplasmic membrane of Psycrophiles are structurally modified in such a way that low temperatures do not inhibit membrane functions • Cytoplasmic membranes from psychrophiles tend to have a higher content of unsaturated and shorter-chain fatty acids • Ex: Psychroflexus contains fatty acids with up to five double bonds

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Microbial Life in the Cold • Other adaptations  cold-shock proteins  helping the cell maintain other proteins in an active from under cold conditions or binding to specific mRNAs and facilitating their translation • Cryoprotectants  these agent help prevent the formation of ice crystal that can puncture (kebocoran) the cytoplasmic membrane • Cryoprotectants include dedicated antifreeze proteins or specific solutes, such as glycerol or certain sugars that are produced in large amounts at cold temperature

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Microbial Life at High Temperatures • Organisms whose growth temperature optimum exceeds 45oC are called thermophiles and those whose optimum exceeds 80oC are called hyperthermophiles • Their enzymes and othe proteins are much more heat stable than are those of mesphiles and actually function optimally at high temperatures • Studies of several heat stable enzymes have shown that they often differ very little in amino acid sequence from heat sensitive forms of the enzymes that catalyze the same reaction in mesophiles

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Acidity & Alkalinity • A critical factor governing acidophily is the stability of the cytoplasmic membrane  when the pH is raised to neutrality, the cytoplasmic membranes of strongly acidophilic bacteria are destroyed and the cell lyse Ex: Picrophilus oshimae (grows optimally at pH 0.7 and 60oC, above pH 4, cells spontaneously lyse • Alkaliphiles  Bacillus such as Bacillus firmus (pH range from 7,5 – 11)  proton motive force • Alkaliphiles have industrial uses because they produce hydrolityc enzymes such as protease & Lipases

Osmotic Effects • When an organism grows in a medium with a low water activity, it can obtain water from its environment only by increasing its internal solute concentration and driving water by osmosis • The internal solute concentration can be raised by either pumping solutes into the cell from the environment or by synthesizing a solute • Staphylococcus  halotolerant (7,5 – 10% NaCl)  use prolin (Amino acid) as a compatible solute

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Oxygen • Oxygen is a powerful oxidant and the best electron acceptor for respiration, but O2 can also be a poison to obligate anaerobes. • One major form of toxic oxygen is singlet oxygen (1O2), a higher-energy form of oxygen in which outer shell electrons surrounding the nucleus become highly reactive and can carry out spontaneous and undesirable oxidations within the cell. • Singlet oxygen is produced both photochemically and biochemically, the latter through the activity of various peroxidase enzymes.

Biofilm

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Biofilm

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TERIMAKASIH

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