Why count Bacteria: quickly, easily and accurately?

Kunnen, T.H., Moodley, G.K. Robertson-Andersson, D.V

University of KwaZulu-Natal

Abstract

The microbial loop conceptualizes the pathways of nutrients and energy flow between the microscopic organisms within aquatic ecosystems and primarily revolves around the recycling of organic nutrients into inorganic nutrients by the heterotrophic bacteria. This cycling of nutrients enables ecosystems to function at a relatively stable rate in the absence of allochthonous sources of nutrients, which although essential, are heavily dependent on rain and wind driven modes of transport. The food web is reliant on the lower trophic level to sustain the next higher level for growth and reproduction. Although phytoplankton have received attention as the primary producers of aquatic environments, considerably less attention has focussed on the essential link between the primary producers and the primary recyclers within the global food web. Heterotrophic bacteria are the means by which used nutrients (waste products, sloppy feeding, etc) are recycled into a usable form which can then be re–introduced into the ecosystem for use by both phytoplankton and other biota instead of being lost from the system. The need to rapidly and accurately count and size bacteria within an aquatic ecosystem is key to understanding the direct links between the primary recyclers and producers as well as other biota within the food web and ecosystem carbon linkages. Bacterial numbers, biomass and productivity illustrates; the general health of the ecosystem; nutrient status, predator prey interactions and carbon input of the system. Traditional enumeration of bacteria is tedious and time consuming. We present here the use of image analysis macros to count and measure the length and width of each bacterial cell. This method resulted in a time saving of 7 – 11 months. The macros will be described and its applications discussed.

Keywords: microbial loop, bacteria, counting, food web, ecosystem