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Word Wednesday: Bacteria and Prokaryotes

Wednesday, March 9th, 2016

Bacteria, microbes, prokaryotes – no matter what you call them, we can’t live without them…

Have you thanked a bacterium today? Without bacteria, life as we know it would cease to exist. Organic matter would not breakdown and eventually we would run out of the raw materials for life. So knowing what the bacteria are doing is essential to understanding how an ecosystem works - and how it has been affected when an event (disturbance) like the Deepwater Horizon has occurred.

But what are bacteria? The word bacteria refers to a group of microscopic organisms, typically consisting of a single cell. As they are microscopic, they are also sometimes referred to as microbes (mikros for small, + bios for life).

Microscopic view of a bacterial cell cluster. Photo credit:P. Sobecky

Bacterial cells have a structure that is very different from the cells found in our bodies. The cells in humans, sharks, fishes, oysters, trees and even salt marsh grasses have a complex structure termed eukaryotic. Eukaryotic cells have a nucleus and other organelles enclosed by a membrane, DNA that is wrapped in a matrix of specific proteins and a 2 layer exterior cell membrane that may or may not be surrounded by a cell wall. In contrast, bacteria have a simpler structure termed prokaryotic. Prokaryotic cells have a single, circular, and naked (without histone proteins) DNA molecule that is not contained within a nucleus. Prokaryotic cells are believed to be the oldest cells on Earth. Thus, all bacteria are prokaryotic, but not all prokaryotes are bacteria. The other major group of prokaryotes is the blue green algae (also known as cyanobacteria).

Phylogenetic tree
Phylogenetic tree from Scanlan et al. 2009. Microbiology and Molecular Biology Reviews. v73(2):249-299. Advances in molecular techniques have increased scientist’s ability to identify different species of bacteria.

The microscopic prokaryotes are typically much smaller than eukaryotic cells. Thus, unlike different species of fish or trees, it is difficult to visually distinguish one species of bacteria from another. Historically, distinguishing one species from another was done of the basis of shape and size and later on the characteristics of the cell wall. However, with the development and refinement of molecular techniques, including gene sequencing, and the increase in computing power, the cost of molecular analyses has decreased, and accessibility has increased, and more scientists are studying microbial communities using these techniques.

ACER scientists are investigating the microbial community structure (who is there and how many of them are there) seasonally by sampling three coastal habitats - salt marshes, intertidal unvegetated sediments and seagrasses - in oiled and non-oiled areas. They are also measuring rates of processes that are carried out by bacteria including denitrification. What is denitrification? Well that’s a story for another day!