Endophytic bacteria (Part 2)

Plant Growth Promotion  

In the previous post we saw how plants, as well as animals and humans, are colonised by microorganisms with which they establish relationships that are often fundamental for their metabolism.

Endophytic bacteria have the ability to colonise inside plants and establish a special type of relationship in which both organisms can benefit from this interaction (REITER and SESSITSCH, 2006).

Root segment of Arabidopsis thaliana intensively colonised by Azospirillum  brasilense Az39 (Fluorescent cells) labelled with GFP.

Azospirillum brasilense Az39 labeled with GFP in Arabidopsis thaliana roots

Some endophytic bacteria act by stimulating plant development, they are known as Plant Growth Promoting Bacteria (PGPB).

Previous studies have indicated that endophytic bacteria can promote plant growth by altering plant physiology, including regulation of osmotic pressure, changes in stomatal responses, adjustment in root size and morphology, modification, accumulation and metabolism of nitrogen, and increased uptake of certain minerals (COMPANT et al., 2005; COMPANT et al., 2010).

Endophytic bacteria possess different mechanisms for growth promotion including: phosphate solubilising activity (VERMA et al., 2001; WAKELIN et al., 2004), phytohormone production (LEE et al., 2004), biological nitrogen fixation (COMPANT et al., 2005), siderophore biosynthesis (LODEWYCKX et al., 2002) and the supply of essential nutrients (PUENTE et al., 2009b).

Growth-promoting bacteria produce phytohormones such as indoleacetic acid (IAA) that suppress plant stress. In addition, they improve the nutritional status of the plant due to the presence of activities such as N2 fixation, PO4- solubilisation and siderophore production (SESSITSCH et al., 2013).

On the other hand, endophytic bacteria can also promote plant growth as a consequence of the expression of enzymes (enzyme 1-aminocyclopropane-1carboxylate (ACC) deaminase) key for the metabolism of α-ketobutyrate and ammonia and thereby decrease ethylene levels in host plants (SESSITSCH et al., 2005; SUN et al., 2009).

Endophytic bacteria population on leaves, stems and roots

Population density of endophytic bacteria in Colosoana (Bothriochloa pertusa) grass tissue located in the municipality of Corozal, Colombia. 2012

Bacteria such as Pseudomona putida and Pseudomona fluorescens have been identified as having growth-promoting activities through their metabolic versatility and their ability to use various substrates released by the plant for their development.

In addition, they have short generation time, high mobility, biological nitrogen fixation, ability to colonise roots and production of secondary metabolites that can regulate plant growth and regulate rhizospheric microbial populations (KAPULNIK, 2002).

Also, several groups of microorganisms such as Azetobacter sp., Azospirillum sp., Azoarcus sp., Klebsiella sp., Bacillus sp., Pseudomonas sp., Arthrobacter sp., Enterobacter sp., Burkholderia sp., Serratia sp. and Rhizobium sp. are considered PGPB`s (KLOEPPER, 1983).

At Arvensis we develop Biofertilisers based on PGPB Endophytic Bacteria such as FERTTYBYO (Azospirillum brasiliense, exclusive strain: ARV20) and MYCROTTRON (Pseudomona putida).

D.LAHOZ