Bacterial Ecology


Bacterial ecology is concerned with the interactions between bacteria and their biological and nonbiological environments and with the role of bacteria in biogeochemical element cycling. Many fundamental properties of bacteria are consequences of their small size. Thus, they can efficiently exploit very dilute solutions of organic matter and their potential growth rates are very high. Bacteria do not have a cytoskeleton and they are covered by a rigid cells wall. Therefore they can only take up dissolved low‐molecular‐weight compounds from their surroundings; when bacteria exploit polymeric compounds these must first be undergo extracellular hydrolysis. Bacteria have a great diversity with respect to types of metabolism that far exceeds the metabolic repertoire of eukaryotic organisms. Bacteria play a fundamental role in the biosphere and certain key processes such as, for example, the production and oxidation of methane, nitrate reduction and fixation of atmospheric nitrogen are exclusively carried out by different groups of bacteria. Some bacterial species – ‘extremophiles’ – thrive in extreme environments in which no eukaryotic organisms can survive with respect to temperature, salinity or pH.

Key Concepts:

  • Fundamental properties of bacteria are related to their small size and lack of cytoskeleton.

  • Bacteria display a great diversity in types of metabolism.

  • Bacteria play a key role in the biosphere in terms of transfer of matter and energy.

  • A number of fundamental biogeochemical processes are carried exclusively by bacteria.

  • Bacteria play an important role in all types of habitats including some that cannot support eukaryotic life.

Keywords: bacteria; biogeochemical cycling; microbial ecology; microbial loop; prokaryotes; symbiosis; syntrophy

Figure 1.

A simplified presentation of the vertical zonation of microbial respiration processes in an aquatic sediment. [CH2O] represents organic matter. In the oxic surface layer degradation takes place by oxygen respiration, which prevails because it is the energetically most favourable process. Since the vertical transport of oxygen is due to molecular diffusion it is quickly depleted, sometimes less than 1–2 mm beneath the surface. Other terminal electron acceptors then take over in a succession that reflects the descending energy yield of the involved respiration processes. In marine sediments sulfate reduction predominates quantitatively due to the high concentration of SO42− in seawater; in other systems methanogenesis plays an important role.

Figure 2.

A vertically cut slice of a 7‐mm‐thick cyanobacterial mat. The green colour of the top millimetre is due to filamentous cyanobacteria (the darker green towards the bottom part of this layer reflects higher pigment contents caused by exposure to lower light intensities). White carbonate precipitations are seen beneath the green layer. The purple colour of the middle part of the mat is due to photosynthetic purple bacteria; below them a green–brown colour discloses the presence of green sulfur bacteria.

Figure 3.

Mass occurrence of purple sulfur bacteria on the top of decaying seaweeds in a shallow bay. These photosynthetic bacteria depend on light and on sulfide as a reductant.

Figure 4.

The filamentous colourless sulfur bacterium Beggiatoa on the top of a sandy sediment (individual sand grains measure about 200 μm). A few colonies of the purple sulfur bacterium Thiocapsa are also visible.

Figure 5.

The microbial loop: in most ecological systems a substantial fraction of the primary production is first degraded by bacteria. In the process bacterial biomass is generated and this enters the food chains, typically via bacterivorous protozoa although virus is also a significant mortality factor for bacteria.



Armitage JP and Lackie JM (eds) (1990) Biology of the Chemotactic Response. Cambridge: Cambridge University Press.

Chivian D, Brodie EL, Alm EJ et al. (2008) Environmental genomics reveals a single‐species ecosystem deep within Earth. Science 322: 275–278.

Conrad R (1996) Soil microorganisms as controllers of atmospheric trace gases (H2, CO2, CH4, OCS, N2O, NO). Microbiological Reviews 60: 609–640.

Dalsgaard T, Thamdrup B and Canfield DE (2005) Anaerobic ammonium oxidation (anammox) in the marine environment. Research in Microbiology 156: 457–464.

DeLong EF and Béjà O (2010) The light driven proton pump proteorhodopsin enhances bacterial survival during tough times. PLoS Biology 8(4): e1000 doi:10.1371/journal/pbio.1000359.

Falkowski P, Fenchel T and DeLong EF (2008) The microbial engines that drive Earth's biogeochemical cycles. Science 320: 1068–1071.

Fenchel T (2002) Microbial behaviour in a heterogeneous world. Science 296: 1068–1071.

Ghiorse WC (1997) Subterranean life. Science 275: 789–791.

Kirchman DL (ed.) (2008) Microbial Ecology of the Oceans, 2nd edn. Hoboken, NJ: Wiley‐Blackwell.

Kolber ZS, Gerald F, Plumley AS et al. (2001) Contribution of aerobic phototrophic bacteria to the carbon cycle in the ocean. Science 292: 2492–2495.

Schultz HN and Jørgensen BB (2001) Big bacteria. Annual Review of Microbiology 55: 105–137.

Southward EC (1987) Contribution of symbiotic chemoautotrophs to the nutrition of benthic invertebrates. In: Sleigh MA (ed.) Microbes in the Sea, pp. 83–118. New York: Wiley.

Staley JT and Gosink JJ (1999) Poles apart: biodiversity and biogeography of sea ice bacteria. Annual Review of Microbiology 53: 189–215.

Further Reading

Dworkin M, Falkow S, Rosenberg E, Schleifer H‐K and Stackebrandt E (eds) (2006) The Prokaryotes, 2nd edn, vols 1–4. New York: Springer.

Edwards C (ed.) (1990) Microbiology of Extreme Environments. New York: McGraw Hill.

Fenchel T and Finlay BJ (1995) Ecology and Evolution in Anoxic Worlds. Oxford: Oxford University Press.

Fenchel T, King GM and Blackburn TH (1998) Bacterial Biogeochemistry. The Ecophysiology of Mineral Cycling, 2nd edn. San Diego, CA: Academic Press.

Hobson PN (ed.) (1989) The Rumen Microbial Ecosystem. London: Elsevier.

Koch AL (1990) Diffusion. The crucial process in many aspects of the biology of bacteria. Advances in Microbial Ecology 11: 37–70.

Madigan MT, Martinko JM, Stahl D et al. (2011) Biology of Microorganisms, 13th edn. Upper Saddle River, NJ: Prentice Hall.

Postgate J (1982) The Fundamentals of Nitrogen Fixation. Cambridge: Cambridge University Press.

Smith DC and Douglas AE (1987) The Biology of Symbiosis. London: Edward Arnold.

Tate RL (1995) Soil Microbiology. New York: Wiley.

Contact Editor close
Submit a note to the editor about this article by filling in the form below.

* Required Field

How to Cite close
Fenchel, Tom(Sep 2011) Bacterial Ecology. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0000339.pub3]