Friends with benefits – the role of endophytic bacteria in legume nodules containing nitrogen-fixing rhizobia

From shoot to root plants are exposed to a diverse range of microorganisms, which can play a major role in plant health, growth and development.

A small fraction of bacteria can cause disease, the vast majority of bacteria has no known effect on the host, but there are bacteria that are beneficial to the plant. These microbes are able to protect plants from pathogens, modulate immune responses or assist in nutrient uptake.

The best studied beneficial relationship for both plant and bacteria, is the long-term biological interaction (symbiosis) between legumes and nitrogen-fixing bacteria.

These bacteria called rhizobia, are hosted in root nodules of legumes such as clover or alfalfa, where they fix atmospheric nitrogen.

However, rhizobia are not the sole occupants of nodules and despite early findings of the presence of other nodule associated bacteria (NAB), the diversity and role of NAB in symbiosis and plant growth has remained neglected.

Legumes are important crop in agriculture worldwide and as such, the potential of plant growth promoting bacteria and increase of nitrogen-fixation abilities is a major topic of research aiming to enhance agricultural productivity.

Investigating the genetic material of all the microbes, the so-called microbiome, of legume root nodules, will allow investigation of genetic features of those bacteria, which contribute to increased plant growth and nutrient availability.

Here, I will use a holistic sequencing approach to (i) unravel the diversity and metabolic properties of NAB in legume nodules and (ii) gain insights into the environmental factors affecting NAB community composition, (iii) determine to what extent the bacterial community in the soil (rhizosphere) drives nodule community composition.

The proposed research will provide a better understanding of the biological role of all co-occurring bacteria in nodules, in the otherwise binary interaction of legume-rhizobia symbiosis.