Physiological and biochemical characterization ofAzospirillum brasilensestrains commonly used as plant growth-promoting rhizobacteria

Abstract

Azospirillum is a plant growth-promoting rhizobacteria (PGPR) genus vastly studied and utilized as agriculture inoculants. Isolation of new strains under different environmental conditions allows the access to the genetic diversity and improves the success of inoculation procedures. Historically, the isolation of this genus has been performed by the use of some traditional culture media. In this work we characterized the physiology and biochemistry of five different A. brasilense strains, commonly used as cereal inoculants. The aim of this work is to contribute to pose into revision some concepts concerning the most used protocols to isolate and characterize this bacterium. We characterized their growth in different traditional and non-traditional culture media, evaluated some PGPR mechanisms and characterized their profiles of fatty acid methyl esters and carbon-source utilization. This work shows, for the first time, differences in both profiles, and ACC deaminase activity of A. brasilense strains. Also, we show unexpected results obtained in some of the evaluated culture media. Results obtained here and an exhaustive knowledge revision revealed that it is not appropriate to conclude about bacterial species without analyzing several strains. Also, it is necessary to continue developing studies and laboratory techniques to improve the isolation and characterization protocols.

Plant growth-promoting rhizobacteria inoculation and nitrogen fertilization increase maize (Zea mays L.) grain yield and modified rhizosphere microbial communities

“…These results could be explained by phosphorous fertilization to the entire experimental plot at sowing, which could be affect commercial inoculation response due to phosphate solubilization is one of the plant growth promotion mechanisms of P. fluorescens (Antoun and Prévost, 2006). Also, the A. brasilense strains included in the commercial inoculant -Az39-have not been isolated from corn and it showed to be very phenotypically (Di Salvo et al, 2014) and genotypically (Jijón-Moreno et al, 2015) different to the 40 M and 42 M strains. As it was reported, these two strains have shown to produce higher levels of indole-acetic acid than Az39 strain (Jijón-Moreno et al, 2015).…”

“…Both strains were previously isolated from maize rhizosphere (García de Salamone and , identified (García de Salamone et al, 2010) and vastly characterized (Di Salvo et al, 2014;García de Salamone 2012a,b). Experimental inoculants were a liquid formulation of NFb medium with 1 g L −1 of ammonium chloride (García de Salamone et al, 2010).…”

ISOLATION AND SCREENING OF BACTERIA FROM Zea mays PLANT GROWTH PROMOTERS

“…The rhizosphere is inhabited by large numbers of microorganisms known as plant-growth promotingrhizobacteria (PGPR) (Di Salvo et al 2014, Gupta et al 2014) that significantly stimulate plant growth through direct or indirect mechanisms. The direct mechanisms include biofertilization, stimulation of root growth, rhizo-remediation and plant stress control (Labra-Cardón et al 2012, Vacheron et al 2013.…”

“…Rhizobium (Yadegari et al 2008, Schwachtje et al 2011, López-Ortiz et al 2012), Frankia, Azotobacter, Pseudomonas (Shim et al 2014, ZuluetaRodriguez et al 2014, Beijerinckia, Alcalisens, Arthobacter, Burkholderia (Poupin et al 2013), Bacillus (Lopez-Bucio et al 2007), Serratia and Azospirillum (Di Salvo et al 2014) and other similar microorganisms commonly used as crop inoculants of agricultural interest. Most of these bacteria produce physiologically active substances that foment seed germination, growth acceleration, and increased crop yield, improving plant defenses against pathogens.…”

Natural occurrence of Azospirillum brasilense in petunia with capacity to improve plant growth and flowering

“…It is known that the level of response to Azospirillum inoculation can be defined by the genetic characteristics of both bacteria and host plant [12]. Thus, it is necessary to obtain new isolates under different environmental conditions with growth‐promoting attributes to explore the genetic diversity and to improve the success of the inoculation procedure [13]. Even more, in view of the worldwide distribution of Azospirillum , the exploitation of yet undiscovered strains may be a useful source of new and more beneficial associations.…”