Microbiology and Immunology

WORLD OF MICROBIOLOGY AND IMMUNOLOGY Petroleum microbiology

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Wilhelm-Akademie for military physicians from 1871 to

1875. He then undertook doctoral training as a subordinate
      physician at the Berlin Charité. He received his doctorate in
      medicine in 1876.
      From 1876 until 1882 Petri practiced as a military
      physician. Also, during this period, from 1877 to 1879, he was
      assigned to a research facility called the Kaiserliches
      Gesundheitsamt. There, he served as the laboratory assistant to
      Robert Koch. It was in Koch’s laboratory that Petri acquired
      his interest in bacteriology. During his stay in Koch’s labora-
      tory, under Koch’s direction, Petri devised the shallow, cylin-
      drical, covered culturedish now known as the Petri dish or
      Petri plate.
      Prior to this invention, bacteria were cultured in liquid
      broth. But Koch foresaw the benefits of a solid slab of medium
      as a means of obtaining isolated colonies on the surface. In an
      effort to devise a solid medium, Koch experimented with slabs
      of gelatin positioned on glass or inside bottles. Petri realized
      that Koch’s idea could be realized by pouring molten agarinto
      the bottom of a dish and then covering the agar with an easily
      removable lid.
      While in Koch’s laboratory, Petri also developed a tech-
      nique for cloning(or producing exact copies) of bacterial
      strains on slants of agar formed in test tubes, followed by sub-
      culturing of the growth onto the Petri dish. This technique is
      still used to this day.
      Petri’s involvement in bacteriology continued after
      leaving Koch’s laboratory. From 1882 until 1885 he ran the
      Göbersdorf sanatorium for tuberculosispatients. In 1886 he
      assumed the direction of the Museum of Hygienein Berlin,
      and in 1889 he returned to the Kaiserliches Gesundheitsamt as
      a director.
      In addition to his inventions and innovations, Petri pub-
      lished almost 150 papers on hygiene and bacteriology.
      Petri died in the German city of Zeitz.

See alsoBacterial growth and division; Growth and growth

media; Laboratory techniques in microbiology

PPetroleum microbiologyETROLEUM MICROBIOLOGY

Petroleum microbiology is a branch of microbiology that is

concerned with the activity of microorganismsin the forma-

tion, recovery, and uses of petroleum. Petroleum is broadly

considered to encompass both oil and natural gas. The

microorganisms of concern are bacteriaand fungi.

Much of the experimental underpinnings of petroleum

microbiology are a result of the pioneering work of Claude

ZoBell. Beginning in the 1930s and extending through the late

1970s, ZoBell’s research established that bacteria are impor-

tant in a number of petroleum related processes.

Bacterial degradation can consume organic compounds

in the ground, which is a prerequisite to the formation of

petroleum.

Some bacteria can be used to improve the recovery of

petroleum. For example, experiments have shown that starved

bacteria, which become very small, can be pumped down into

an oil field, and then resuscitated. The resuscitated bacteria

plug up the very porous areas of the oil field. When water is

subsequently pumped down into the field, the water will be

forced to penetrate into less porous areas, and can push oil

from those regions out into spaces where the oil can be

pumped to the surface.

Alternatively, the flow of oil can be promoted by the use

of chemicals that are known as surfactants. A variety of bacte-

ria produce surfactants, which act to reduce the surface tension

of oil-water mixtures, leading to the easier movement of the

more viscous oil portion.

In a reverse application, extra-bacterial polymers, such

as glycocalyxand xanthan gum, have been used to make water

more gel-like. When this gel is injected down into an oil for-

mation, the gel pushes the oil ahead of it.

A third area of bacterial involvement involves the mod-

ification of petroleum hydrocarbons, either before or after col-

lection of the petroleum. Finally, bacteria have proved very

Oil spill from a damaged vessel (in this case, the Japanese training

ship Ehime Maruafter it was rammed by the American military

submarine USSGreenevillenear Hawaii).

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