Bacillus simplex—A Little Known PGPB with Anti-Fungal Activity—Alters Pea Legume Root Architecture and Nodule Morphology When Coinoculated with Rhizobium leguminosarum bv. viciae

Abstract

Two strains, 30N-5 and 30VD-1, identified as Bacillus simplex and B. subtilis, were isolated from the rhizospheres of two different plants, a Podocarpus and a palm, respectively, growing in the University of California, Los Angeles (UCLA) Mildred E. Mathias Botanical Garden. B. subtilis is a well-known plant-growth promoting bacterial species, but B. simplex is not. B. simplex 30N-5 was initially isolated on a nitrogen-free medium, but no evidence for nitrogen fixation was found. Nevertheless, pea OPEN ACCESSAgronomy 2013, 3 596 plants inoculated with B. simplex showed a change in root architecture due to the emergence of more lateral roots. When Pisum sativum carrying a DR5::GUSA construct, an indicator for auxin response, was inoculated with either B. simplex 30N-5 or its symbiont Rhizobium leguminosarum bv. viciae 128C53, GUS expression in the roots was increased over the uninoculated controls. Moreover, when pea roots were coinoculated with either B. simplex 30N-5 or B. subtilis 30VD-1 and R. leguminosarum bv. viciae 128C53, the nodules were larger, clustered, and developed more highly branched vascular bundles. Besides producing siderophores and solubilizing phosphate, the two Bacillus spp., especially strain 30VD-1, exhibited anti-fungal activity towards Fusarium. Our data show that combining nodulating, nitrogen-fixing rhizobia with growth-promoting bacteria enhances plant development and strongly supports a coinoculation strategy to improve nitrogen fixation, increase biomass, and establish greater resistance to fungal disease.

The Nodule Microbiome: N2-Fixing Rhizobia Do Not Live Alone

“…Bacillus simplex strains were reported to have PGP activities and have been isolated as endophytes from various plants and also reisolated from pea nodules in coinoculation experiments with Rhizobium leguminosarum bv. viciae (Schwartz et al 2013 and references therein). Deep analyses of NAB genomes may provide insights into understanding the involvement of many understudied microbes in plant growth and survival.…”

“…Also, nodules of Hedysarum, a forage legume, were found to harbor Enterobacter cloacae, Enterobacter kobei, Escherichia vulneris, Pantoea agglomerans, and Leclercia adecarboxylata (Muresu et al 2008). Because it has long been known that coinoculation of rhizobia and other bacteria, particularly Bacillus species, promotes not only nodulation (Schwartz et al 2013 and papers cited therein), but also N availability in sustainable agricultural systems (Rajendran et al 2012), it is assumed that many of the nonpathogenic bacteria found within nodules or in plant tissues as endophytes could be safe and effective partners for enhancing nitrogen fixation in legumes (Sturz et al 2000).…”

Bioremediation Potential Assessment of Plant Growth-Promoting Autochthonous Bacteria: a Lignite Mine Case Study

“…Our data show that root exudates significantly affect microbial abundance in soil, as reported elsewhere [31]. Given that members of the Bacillus genus exhibit PGP activities [24,32], we used 13k/19k to co-inoculate the seeded substrates. The co-inoculum caused an increase in the total number of microorganisms in 100% OS from 2.45x10 6 to 3.12x10 6 CFU/g (oat) and from 2.02x10 6 to 3.12x10 6 CFU/g (lettuce) (Fig.…”

“…To our knowledge, this represents the first microbial characterization of mine waste in BiH. Previous research has demonstrated the ability of B. simplex to accumulate metals, such as Cd, Co, Ni, and Sr [36], as well as to promote plant growth by altering plant root architecture, i.e., by stimulating the emergence of more lateral roots [24]. Studies have also shown PGP activities of B. cereus [37] and other group members, such as B. thuringiensis [38], as well as the potential role of B. thuringiensis in biodegradation of organophosphorus in contaminated soil [39].…”

“…Unlike the majority of previous research on plant growth promoting (PGP) microorganisms, which focused on Gram negative bacteria [23,24], we decided to explore ammonifying bacteria. Macroscopic investigation of MPA plates resulted in two types of morphologically distinguishable colonies: 13k and 19k.…”