Gram-/+
Bacteria can be divided into two distinct groups:
- Gram-negative (Gram-)
- Gram-positive (Gram+)
Gram+ bacteria are generally larger than Gram- bacteria and can form spores. This makes them more resistant to drought and water stress. Gram positive bacteria are dominant when there is a higher Gram+/Gram- ratio (>1) and are more common at the beginning of the growing season. When the soil conditions become more favorable, this will balance again.
At a lower Gram+/Gram- ratio, the gram- are dominant. These are often associated with other forms of stress, such as ploughing and pesticide use. Gram bacteria can better tolerate these types of disturbance due to the presence of an outer membrane.