In terms of biogeochemical cycles as well as "ecosystem services" (ecological functions of benefit to human kind; Hooper
et al. 2005), bacteria reign supreme. These primitive cells lack nuclei and other organelles such as mitochondria, yet they
display the most diverse range of enzymatic and biochemical functions on our planet. How many species there might actually
be is still a subject of much conjecture. A recent analysis suggests that world ocean may contain up to 10,000 taxa, most of
which are extremely rare ("the rare biosphere"), while core ecosystem functions are mostly performed by a small and variable
minority (Pedr ós-Ali ó, 2006). Apart from the pathogenic role of some species, their myriad of functions include recycling
nutrients, decomposing wastes, fixing and transforming nitrogen, producing and oxidizing methane, and providing a carbon
and nutrient source to other microscopic organisms (especially protists) at the bottom of the food web. Bacteria are
also the most abundant cell type on the planet. Even our own bodies contain more bacterial cells than human cells,
and an estimate of the total number of bacteria on Earth is 5 million trillion trillion (5 x 1030 cells; Whitman et al. 1998).
Little wonder that bacteria are the primary biological agents that keep the world working.
From left to right: Petri dish with colonies of pigmented bacteria (from this website);
Epifluorescence micrograph of a water sample treated with the fluorescent stain SYBR Green I and showing the large concentrations of viruses (smaller dots) and bacteria and archaea (from this website);
Scanning electron micrograph of a rod-shaped bacterium (from this website);
Structure of a bacterial cell (from this website);
It used to be thought that the Polar Regions would be a tough place for bacteria, with low temperatures causing a severe
depression of their metabolism and growth. However, many species appear to be cold tolerant (psychrotrophic) and some are
even highly adapted to the cold, and grow only at low temperatures (psychrophilic). In organic rich waters such as large
arctic rivers and their floodplain lakes, bacterial production of carbon dioxide exceeds that used by photosynthesis,
and these ecosystems are net sources of CO2 to the atmosphere. In aquatic ecosystems in general, bacteria are typically
present in concentrations around 10 million cells per litre of water. DNA analysis is providing many new insights
into the enormous diversity of bacteria in lakes and seas, and most have yet to be brought into culture.
References:
Hooper D.U. et al. (2005). Effects of biodiversity on ecosystem functioning: A consensus of current knowledge. Ecological Monographs 75: 3-35.
