heterotrophic behaviour. The higher on the evolutionary ladder, the more
complex metabolic pathways are found including new enzymes, cycles, etc.
The view that is prevailing in our day is that the first live organisms on
Earth were the methane-producing anaerobic bacteria also called archaic.
Some of the characteristics give grounds for that: a) typical autotrophs
which satisfy their needs from water, inorganic sources and CO₂ from the
atmosphere; b) they do not possess any biological means for protection
from atmospheric oxygen (O₂); c) they grow in a wide range of extreme
conditions such as temperatures over 90°C; d) they differ from the other
bacteria in the strongly “conservative” 16S ribosomal RNA (rRNA), which
shows that their evolution has followed a path of their own differing from
that of the others (Woese, Fox, 1977); e) they convert organic matter into
CH₄ and CO₂ (Abbanat et al., 1989).
At this early stage of cell evolution have also emerged cyanobacteria
known as blue-green algae (Chyanophyta). These organisms have the
capacity to fix CO₂ and N₂ from the atmosphere thus synthesizing more
complex compounds. Since the CO₂ and N₂ molecules are very stable and
a great amount of energy is needed for their conversion into a useful
metabolite form, chemical reactions have been greatly elaborated with the
inclusion of new enzymes, pigments and phases of the processes.
Nitrogen fixation capacity preserved in some bacteria and blue-green
algae is an interesting biological phenomenon which if implemented in
genetic engineering for eventual changes in the genome of higher
organisms could lead to a rise in yields from important crops. Besides the
classical type of nitrogen fixation characterized with tuber-formation,
associative nitrogen fixation also provokes great interest. In it the effect is
generated by the interaction of the nitrogen fixing microorganisms living in
the soil with the root rhisosphere of plants.
Accepting the anaerobic methanogenic bacteria as the first “inhabitants”
of the Earth renders an answer to two essential questions having a direct
relevance to the origin of life: 1) the atmosphere of the Earth in the early times
has been devoid of oxygen or its content has only been limited to insignificant
quantities; 2) the first organisms have been developing in the absence of
oxygen utilizing inorganic substances from the environment and CO₂ from the
atmosphere reduced by hydrogen for the synthesis of the organic substances
needed. That is why glycolysis in anaerobic conditions which is a chain of
chemical reactions effectuating carbohydrate degradation in the absence of
oxygen can be regarded as the most ancient metabolic pathway.
It must be noted that even in our day glycolysis is taking place in all
living cells, but the mechanisms have become two. The already mentioned
anaerobic one results in fermentation products (methane, alcohols or lactic
acid) and the other one — aerobic (with the participation of oxygen) where
carbohydrates (sugars) are degraded to CO₂ and H2O (Fig. 1–8).