Comparative assessment of multi-trait plant growth-promoting endophytes associated with cultivated and wild Oryza germplasm of Assam, India

This paper presents a comparative study of endophytic bacteria from cultivated (Oryza sativa) and wild rice (Oryza rufipogon) plants and their functional traits related to plant growth promotion. A total of 70 bacterial isolates were characterized by both biochemical and molecular identification methods. Taxonomic classification showed dominance of three major phyla, viz, Firmicutes (57.1%), Actinobacteria (20.0%) and Proteobacteria (22.8%). Screening for in vitro plant growth-promoting activities revealed a hitherto unreported endophytic bacterium from wild rice germplasm, Microbacterium laevaniformans RS0111 with highest indole acetic acid (28.39 ± 1.39 µg/ml) and gibberellic acid (67.23 ± 1.83 µg/ml) producing efficiency. Few other endophytic isolates from cultivated rice germplasm such as Bacillus tequilensis RHS01 showed highest phosphate solubilizing activity (81.70 ± 1.98 µg/ml), while Microbacterium testaceum MKLS01 and Microbacterium enclense MI03 L05 showed highest potassium (53.42 ± 0.75 µg/ml) and zinc solubilizing activity (157.50%). Fictibacillus aquaticus LP20 05 produced highest siderophore (64.8%). In vivo evaluation of plant growth-promoting efficiencies of the isolates showed that Microbacterium laevaniformans RS0111, Microbacterium testaceum MKLS01 and Bacillus tequilensis RHS 01 could increase rice grain yield by 3.4-fold when compared to the control group. This study indicates the potentiality of rice endophytes isolates as an effective bioinoculants.

Antagonic and plant growth-promoting effects of bacteria isolated from mine tailings at El Fraile, Mexico

Mine tailings contain high concentrations of heavy metals such as As, Pb, Cu, Mn, and Fe, which are detrimental to the health of humans and the environment. In tailings at the El Fraile mine in Guerrero, Mexico, some plant species are apparently tolerant of heavy metals and can be found growing in the tailings. These plants could be associating with heavy metal-tolerant bacteria that promote plant growth and improve biomass production, and these bacteria could be a useful alternative for bacteria-assisted phytoremediation. The objective of this study was to isolate bacteria detected in the mine tailings at El Fraile-Taxco, focusing on those in the soil from the rhizosphere, the inner tissue of the root, leachate, and water, which have the potential to promote plant growth. The ability of the isolated bacteria to promote plant growth was evaluated in vitro. Of the 151 morphotypes isolated, 51% fix nitrogen, 12% dissolve phosphates, and 12%, 39.7%, and 48.3% produce indole acetic acid, gibberellins, and siderophores, respectively. In addition, 66.7% were observed to produce lytic enzymes, such as proteases, celluloses, lipases, esterases, and amylases, which exhibited activity against Fusarium, Aspergillus, and Colletotrichum. The use of 16S rRNA analysis led to the identification of the bacterial genera Chryseobacterium, Bacillus, Pseudomonas, Mycobacterium, Staphylococcus, Curtobacterium, Enterobacter, Agrobacterium, Ochrobactrum, Serratia, Stenotrophomonas, and Acinetobacter. The bacteria isolated from the rhizosphere exhibited the greatest ability to fix nitrogen and produced indole acetic acid, gibberellins, siderophore, and lytic enzymes. In addition, the isolates collected from the soil samples demonstrated ability to solubilize phosphate.