Rosas S.B. International Biology Review, vol. 1, issue 3, December 2017 Page 1 of 19 REVIEW ARTICLE Pseudomonas chlororaphis subsp. aurantiaca SR1: isolated from rhizosphere and its return as inoculant. A review Susana B. Rosas Affiliation: Departamento de Biología Molecular, Universidad Nacional de Río Cuarto, Campus Universitario, Ruta 36, Km 601, 5800 Río Cuarto, Cba, Argentina Corresponding e-mail address: [email protected] Abstract Most pseudomonas isolated from the plant rhizosphere favor the growth of plants through direct and indirect mechanisms. These bacteria produce phytohormones that promote plant growth and produce secondary metabolites that inhibit the growth of pathogenic bacteria and fungi, ensuring crop health. The present review is a compilation on the characterization of Pseudomonas aurantiaca SR1 and its role in the promotion of growth on several crops and its capacity to produce secondary metabolites involved in the control of pathogenic fungi. Pseudomonas aurantiaca SR1, a subspecies of Pseudomonas chlororaphis, produces IAA, HCN, siderophores, phenazines, and quorum, among other abilities. It has shown antifungal activity against several pathogenic strains, among them, Fusarium, Pythium, Rhizoctonia and Sclerotium spp. The SR1 aurantiaca strain has been shown to be a plant growth promoter for various crops, such as alfalfa, wheat, soybean, maize, carob, sugar cane, as well as promoting germination and obtaining vigorous and healthy seedlings. Pseudomonas chlororaphis subsp. aurantiaca SR1 is currently marketed as PSA liquid from BIAGRO-BAYER Laboratory. Keywords: Pseudomonas aurantiaca SR1, growth promotion, biocontrol, inoculant, crops, seedling 1. Introduction The interactions between the plants and the Natural agricultural ecosystems depend microorganisms have undoubtedly big directly on beneficial microorganisms that effects on the development of humanity, are present in the soil rhizosphere and help given that man for his survival needs to crops to reach higher productivities. The increase every day the agricultural beneficial microorganisms of the rhizosphere productions for nutritive ends, between are important determinants of plant health others. and soil fertility because of their At the global level, phytopathogenic fungi participation in several key processes such as are the most economically important group those involved in the biological control of in terms of frequency of appearance and plant pathogens, nutrient cycling and damage that they can cause. The damage seedling establishment [1]. they cause not only refers to the loss of Copyright 2017 KEI Journals. All Rights Reserved http://journals.ke-i.org/index.php/IBR Rosas S.B. International Biology Review, vol. 1, issue 3, December 2017 Page 2 of 19 economic production, but also to the losses least partially, the practices used by new of biological production [2] and have caused methods. havoc and major social changes. But Although PGPRs have been classified agricultural diseases, although arising from a according to their mechanism to promote mode of interaction between plants and plant growth or to control pathogens, they microorganisms, are not the only example of exert their beneficial effect by employing a such interactions. A large number of combination of mechanisms to stimulate beneficial relationships make a tremendous growth and maintain plant health [6]. importance for the development of sustainable agriculture. Moreover, through Fluorescent pseudomonades have received beneficial associations between plants and the most attention as candidates for microorganisms, attempts are made to biocontrol agents and biofertilizer due to displace the diseases that affect plants. their ability to colonize surfaces and internal tissues of roots and stems at high densities. The rhizosphere is called the zone adjacent These bacteria can compete successfully to the root system of plants influenced by with soil microorganisms. They are well root exudates [3].The rhizosphere is a site of known for promoting the growth of several intense and complex microbiological plants due to their ability to produce activity. It is an absolutely dynamic indoleacetic acid (IAA) and to solubilize environment due to the constant change in phosphate [7, 8, 9]. Pseudomonas also have the root structures, the exudate profile of the a great capacity to produce secondary root and the balance between the different antifungal metabolites. It is known that more microbial communities. The promotion of than twenty species of Pseudomonas plant growth mediated by PGPR (Plant synthesize more than 100 antibiotics and growth promoting rhizobacteria) is caused aromatic antibiotics [10]. Some well known by the interaction of the entire microbial antibiotics are phenazine-1-carboxylic acid community in the rhizosphere through the (PCA), phenazine-1-carbo-xamide (PCN), production of various substances [4]. In 2,4-diacetyl-phloroglucinol (Phl), pyro- general, PGPR promote plant growth cyanine, 2-aceta-midophenol, pyrrolnitrine, directly either facilitating the acquisition of pyoluteorin [11]. resources (nitrogen, phosphorus and minerals) or modulating hormone levels Siderophores include salicylic acid, plant or indirectly inhibiting deleterious piocheline and pioverdine, which chelate effects of various pathogens on growth and ions and contribute to disease control by development of the plants in the form of limiting the availability of trace minerals biological control agents [5]. Losses in plant required for microbial growth [12]. production caused by fungal diseases are an important economic factor to be considered. 2. Pseudomonas chlororaphis subsp. Historically, control over plant diseases has aurantiaca SR1 been carried out through the use of resistant varieties and agronomic practices, including P. chlororaphis subsp. Aurantiaca SR1 the application of synthetic fungicides and (GenBank accession number GU734089) other agrochemicals. However, ecological was isolated from the rhizosphere of soybean problems arose with risks to human health, in the area of Río Cuarto, Córdoba, contamination of water and selection of Argentina [13, 14]. It was initially classified pathogens with chemical resistance as P. aurantiaca by using the BIOLOG associated with the use of agrochemicals. (Biolog Inc., Hayward, CA) system [15] and This raises the urgent need to replace, at by amplification and sequencing of a partial fragment from the 16S rDNA gene. The Copyright 2017 KEI Journals. All Rights Reserved http://journals.ke-i.org/index.php/IBR Rosas S.B. International Biology Review, vol. 1, issue 3, December 2017 Page 3 of 19 species Pseudomonas aurantiaca was and pltC, genes encoding the production of reclassified as P.chlororaphis subsp. pyrrolnitrin (PRN) and pyoluteorin (PLT), aurantiaca 16]. respectively, were performed as described by It produces siderophores, behaves as an De Souza and Raaijmakers [24]. On the endophyte and is capable of promoting plant other hand, detection of hcnAB genes growth through mechanisms that involve (involved in the biosynthesis of HCN phytohormone-like substances [17]. For synthetase) was performed by PCR using the instance, SR1 shows the ability to produce primers PM2-F5′-TGCGGCATGGGCGC indole 3-acetic acid (16,5 ug. ml-1). In ATTGCTGCCTGG3′) and PM2-R (5′- addition, strain SR1 is able to colonize the CGCTCTTGATCTGCAATTGCAGGC-3′) [25]. As a result, fragments of the predicted root-system of several crops and behaves as an excellent growth promoter in wheat, size for PCA, PRN and HCN were amplified alfalfa, soybean, sugarcane, corn [18, 19, 20] from the DNA of strain SR1. maintaining appropriate population densities 2.1. Pigment production by P. aurantiaca in the rhizospheric area [21]. Its production in different culture media capacity for chitinases has been evaluated, proving that it does not present this property, The carbon sources normally found in root nor does it present conserved secretion exudates have a differential influence on the protein genes type III although spectrum of antibiotics produced by the polyacrylamide gels have been shown to be strains involved in biological control [26, 27, active in secretion of extracellular. The 28]. It is important to note that many other electrophoretic profiles of the LPS show a variables affect biological control, some of model similar to that of the pseudomonas which reside particularly in soil genus with a multiband profile. In addition, physicochemical characteristics such as the ability to fix N2 in P. aurantiaca SR1 moisture, temperature, pH, soil texture and free life was studied, obtaining a positive mineral nutrients; hence the importance of ARA at 24, 48 and 72 hours of incubation the in vitro study of the effects of the under microaerobiosis conditions. The strain chemical composition of the culture medium produces signals Acil type Homoserine and growth conditions on the antifungal lactones (AHL's) [22]. activity. Strain SR1 inhibits a wide range of Macrophomina phaseolina, due to its high phytopathogenic fungal species including sensitivity to P. aurantiaca, was selected to Macrophomina phaseolina, Rhizoctonia spp. evaluate the biocontrol in the media used for T11, Fusarium spp., Alternaria spp., the detection of antifungal activity and the Pythium spp., Sclerotinia minor and correlation with the presence of pigment. Sclerotium rolfsii [15]. In addition, strain The presence of pigment and a marked SR1 is able to colonize the root-system of inhibition (greater than 60%) of fungal several