Gram+/- bacteria
Definition
Bacteria can be divided into two distinct groups:
- Gram-positive (Gram⁺)
- Gram-negative (Gram⁻)
These groups differ in cell wall structure and resistance to environmental conditions.
Gram-positive (Gram⁺) bacteria
Gram(+) bacteria (mg PLFA per kg) are generally larger than Gram(-) bacteria and can form spores. This makes them more resistant to drought and water stress.
Gram(+) dominant populations (>1) are more common at the beginning of the growing season and return to balance when soil conditions become more favourable.
Gram-negative(Gram-) bacteria
Gram- (mg PLFA per kg) dominant populations (<1) are often associated with forms of stress, such as ploughing and pesticide use.
Gram- bacteria can better tolerate these types of disturbances due to the presence of an outer membrane.
Gram⁺ / Gram⁻ ratio
The Gram (+)/Gram (-) ratio (expressed in mg C/kg) is an indication of disturbances and stress.
- A lower ratio, Gram(-) bacteria are dominant. These bacteria are better resistant to disruptions like ploughing and pesticides.
- A high ratio means that Gram(+) bacteria are dominant, these bacteria more resistant to drought and water stress.
- A balanced ratio is achieved when conditions are more favourable.
