Geoscience Reference
In-Depth Information
received little or no attention. Naturally, it is understandable that serious diseases
of man, plants and animals should have been the main focus of investigations, and
that, inevitably, microbes in general became regarded as harmful. Nevertheless, there
are also beneficial microorganisms and many of these occur in soil. During the last
quarter of the nineteenth and early years of the present century, perhaps the most out-
standing scientists who studied soil microorganisms were Sergei Winogradsky who
was active first in Zürich, then in St. Petersburg and later in Paris, and Martinus W.
Beijerinck who worked in Delft in Holland. These two scientists and their co-work-
ers made many important contributions to soil microbiology. Among other problems,
Beijerinck investigated the kinds of bacteria that can fix the inert nitrogen gas of the
atmosphere, converting it into compounds of nitrogen which in turn become plant
nutrients. Winogradsky made many important studies including investigation of the
special bacteria that mediate the oxidation of ammonia to nitrates, that is to say, the
nitrification process.
Table 7
gives a historical summary of discoveries in soil micro-
biology.
T
ABLE 7
Historical perspective of soil microbiology.
1676
Leeuwenhoek first discovered and described bacteria.
Spallanzani made experiments disproving theories of spontaneous gen-
eration.
1769
Schwann and others discovered yeasts and their budding processes: mi-
croorganisms were recognized as the causes of putrefaction and fer-
mentations.
1835-37
Boussingault showed that the nitrogen content of the soil increased on
growing clovers. This did not happen in sterile sand cultures.
1838
De Bary demonstrated the fungal nature of the cereal diseases, rust and
blight.
1853
1857
Pasteur recognized the causative organism of lactic fermentation.
1861
Pasteur distinguished between aerobic and anaerobic organisms.
1872
Cohn devised a classification of bacteria.
1876
Koch identified the germ of anthrax.
