Sulfur-oxidizing buffalo dung bacteria enhance growth and yield of Foeniculum vulgare Mill.

This study aimed to harness the benefits of sulfur-oxidizing beneficial bacteria from buffalo dung to improve crop yields of Foeniculum vulgare. A total of 61 bacterial isolates were screened from buffalo dung, of which 40 isolates exhibited plant-growth-promoting attributes, such as phosphate solubilization, indole-3-acetic acid production, and hydrogen cyanide production. Of these 40, four bacterial isolates, viz., BUFF12, BUFF14, BUFF23, and BUFF38, were the most potent, having plant-growth-promoting and sulfur-oxidizing properties. These four isolates produced phytase by solubilizing calcium phytate and sodium phytate. They solubilized potassium besides oxidizing the sulfur, causing an increase in soil fertility and crop production. All four isolates were nonpathogenic in nature, as demonstrated by a negative haemolysis test. According to the 16S rRNA gene sequence, the isolate BUFF14 was identified as Proteus mirabilis. Proteus mirabilis BUFF14 maximized seed germination with enhanced vegetative and reproductive parameters during pot and field trial studies, compared with the other isolates.

Root nodule bacteria from Clitoria ternatea L. are putative invasive nonrhizobial endophytes.

In this study, bacteria (8 species and 5 genera) belonging to the classes Betaproteobacteria, Gammaproteobacteria, and Sphingobacteria were isolated from root nodules of the multipurpose legume Clitoria ternatea L. and identified on the basis of partial 16S rRNA sequencing. The root nodule bacteria were subjected to phenotypic clustering and diversity studies using biochemical kits, including Hi-Media Carbokit™, Enterobacteriaceae™ identification kit, ERIC-PCR, and 16S ARDRA. All the strains showed growth on Ashby's N-free media over 7 generations, indicative of presumptive nitrogen fixation and further confirmed by amplification of the nifH gene. None of the strains showed the capability to renodulate the host plant, neither alone nor in combination with standard rhizobial strains, which was further confirmed by the absence of nodC bands in PCR assay. The results clearly indicate the common existence of nonrhizobial microflora inside the root nodules of legumes, which were thought to be colonized only by rhizobia and were responsible for N2 fixation in leguminous crops. However, with the recent discovery of nodule endophytes from a variety of legumes, as also observed here, it can be assumed that symbiotic rhizobia are not all alone and that these invasive endophytes belonging to various bacterial genera are more than just opportunistic colonizers of specialized nodule niche.

Beneficial effects of fluorescent pseudomonads on seed germination, growth promotion, and suppression of charcoal rot in groundnut (Arachis hypogea L.).

Rhizobacteria are used as inoculants to enhance crop yield and for biological control of fungal pathogens. Fluorescent pseudomonads isolated from the rhizosphere of groundnut showed suppression of the phytopathogen Macrophomina phaseolina that causes charcoal rot of groundnut, an economically important agroproduct. Two strains of fluorescent pseudomonads, designated as PS1 and PS2, were selected as a result of in vitro antifungal activity. After 5 days of incubation at 28+/-1 degrees , both PS1 and PS2 caused clear inhibition zones in dual cultures, restricting the growth of M. phaseolina by 71% and 74%, respectively. Both the strains were capable of producing siderophores, indole acetic acid, and hydrocyanic acid, and causing phosphate solubilization under normal growth conditions. These strains, when used as inoculants in groundnut, enhanced germination up to 15% and 30% with subsequent increase in grain yield by 66% and 77%, respectively. Conversely, when the pathogen alone was testeds 57% decrease in yield was recorded. Thus the studies revealed the potential of the two pseudomonads not only as biocontrol agents against M. phaseolina, but also as a good growth promoter for groundnut.

Roles of quorum sensing molecules from Rhizobium etli RT1 in bacterial motility and biofilm formation.

Strain RT1 was isolated from root nodules of Lens culinaris (a lentil) and characterized as Rhizobium etli (a Gram-negative soil-borne bacterium) by 16S rDNA sequencing and phylogenetic analysis. The signaling molecules produced by R. etli (RT1) were detected and identified by high-performance liquid chromatography coupled with mass spectrometry. The most abundant and biologically active N-acyl homoserine lactone molecules (3-oxo-C8-HSL and 3-OH-C14-HSL) were detected in the ethyl acetate extract of RT1. The biological role of 3-oxo-C8-HSL was evaluated in RT1. Bacterial motility and biofilm formation were affected or modified on increasing concentrations of 3-oxo-C8-HSL. Results confirmed the existence of cell communication in RT1 mediated by 3-oxo-C8-HSL, and positive correlations were found among quorum sensing, motility and biofilm formation in RT1.

Differential antagonistic responses of Bacillus pumilus MSUA3 against Rhizoctonia solani and Fusarium oxysporum causing fungal diseases in Fagopyrum esculentum Moench.

Chitinase and surfactin-mediated biocontrol of Rhizoctonia solani and Fusarium oxysporum causing wilt and root rot of Fagopyrum esculentum respectively has been studied in this communication. Bacillus pumilus MSUA3 as a potential bacterial strain strongly inhibited the growth of R. solani and F. oxysporum involving the chitinolytic enzymes and an antibiotic surfactin. Plant growth promoting attributes seem to be involved in plant growth promotion and yield attributes. The action of cell-free culture supernatant (CFCS) was found deleterious to F. oxysporum and R. solani even in the heat-treated (boiled/autoclaved) CFCS. The possible involvement of surfactin in disease control was revealed by colony PCR amplification of SrfA. Chitinolytic enzyme and antibiotic surfactin evidenced differential biocontrol of F. oxysporum and R. solani by B. pumilus MSUA3. A significant reduction in disease index under gnotobiotic conditions and productivity enhancement of F. esculentum using vermiculite-based bioformulation revealed B. pumilus MSUA3 as a successful potential biocontrol agent (BCA) and an efficient plant growth promoting rhizobacterium (PGPR) for disease management and productivity enhancement of buckwheat crop.

Roles of quorum sensing molecules from Rhizobium etli RT1 in bacterial motility and biofilm formation

ABSTRACT Strain RT1 was isolated from root nodules of Lens culinaris (a lentil) and characterized as Rhizobium etli (a Gram-negative soil-borne bacterium) by 16S rDNA sequencing and phylogenetic analysis. The signaling molecules produced by R. etli (RT1) were detected and identified by high-performance liquid chromatography coupled with mass spectrometry. The most abundant and biologically active N-acyl homoserine lactone molecules (3-oxo-C8-HSL and 3-OH-C14-HSL) were detected in the ethyl acetate extract of RT1. The biological role of 3-oxo-C8-HSL was evaluated in RT1. Bacterial motility and biofilm formation were affected or modified on increasing concentrations of 3-oxo-C8-HSL. Results confirmed the existence of cell communication in RT1 mediated by 3-oxo-C8-HSL, and positive correlations were found among quorum sensing, motility and biofilm formation in RT1.