Cell-Free Supernatant Obtained From a Salt Tolerant Bacillus amyloliquefaciens Strain Enhances Germination and Radicle Length Under NaCl Stressed and Optimal Conditions

Abstract

Seed germination and early plant growth are key stages in plant development that are, susceptible to salinity stress. Plant growth promoting microorganisms (PGPMs) produce substances, in their growth media, that could enhance plant growth under more optimal conditions, and or mitigate abiotic stresses, such as salinity. This study was carried out to elucidate the ability of a NaCl tolerant Bacillus amyloliquefaciens strain's cell-free supernatant to enhance germination and radicle length of corn and soybean, under optimal and NaCl stressed growth conditions. Three NaCl levels (0, 50, and 75 mM) and four cell-free supernatant concentrations (1.0, 0.2, 0.13, and 0.1% v/v) were used to formulate treatments that were used in the study. There were observed variations in the effect of treatments on mean radicle length and mean percentage germination of corn and soybean. Overall, the study showed that Bacillus amyloliquefaciens (BA) EB2003 cell-free supernatant could enhance mean percentage germination and or mean radicle length of corn and soybean. At optimal conditions (0 mM NaCl), 0.2% BA, 0.13% BA, and 0.1% BA concentrations resulted in 36.4, 39.70, and 39.91%, increase in mean radicle length of soybean, respectively. No significant observations were observed in mean radicle length of corn, and mean percentage germination of both corn and soybean. At 50 mM NaCl, 1.0% BA resulted in 48.65% increase in mean percentage germination of soybean, at 24 h. There was no observed effect of the cell-free supernatant on mean radicle length and mean percentage germination, at 72 and 48 h, in soybean. In corn however, at 50 mM NaCl, treatment with 0.2% BA and 0.13% BA enhanced mean radicle length by 23.73 and 37.5%, respectively. The resulting radicle lengths (43.675 and 49.7125 cm) were not significantly different from that of the 0 mM control. There was no observed significant effect of the cell-free supernatant on mean germination percentage of corn, at 50 mM NaCl. At 75 mM NaCl, none of the treatments enhanced mean radicle length or mean percentage germination to levels significantly higher than the 75 mM NaCl. Treatment with 1.0% BA, however, enhanced mean percentage germination to a level not significantly different from that of the 0 mM control, at 72 h. Likewise, in corn, none of the treatments enhanced radicle length to lengths significantly higher than the 75 mM control, although treatment with 1.0% BA, 0.13% BA, and 0.1% BA elongated radicles to lengths not significantly different from the 0 mM NaCl control. Treatment with 0.2% BA, 0.13% BA, and 0.1% BA resulted in mean percentage germination significantly higher than the 75 mM NaCl by 25.3% (in all 3), not significantly different from that of the 0 mM NaCl. In conclusion, concentration of cell-free supernatant and NaCl level influence the effect of Bacillus amyloliquefaciens strain EB2003A cell-free supernatant on mean percentage germination and mean radicle length of corn and soybean.

Secretome Analysis of the Plant Biostimulant Bacteria Strains Bacillus subtilis (EB2004S) and Lactobacillus helveticus (EL2006H) in Response to pH Changes

“…A decrease in the hydrolase enzyme class representation by 94% ( Table 2 ), as reported here, suggested that some of the enzymes, such as the proteases, which are normally extracellular with a good stability, were not functional [ 69 , 70 ]. Furthermore, bacteria of the Bacillus genus are known for their commercial production of proteases, especially neutral and alkaline ones [ 71 ], which, again, is reflected in the current study in the greater representation of the hydrolase enzyme class at both pH 7 and 8. Some microbes induce components of the Clp protease complex to participate in protein homeostasis by removing the damaged/degraded proteins.…”

Lactobacillus helveticus EL2006H cell-free supernatant enhances growth variables in Zea mays (maize), Glycine max L. Merill (soybean) and Solanum tuberosum (potato) exposed to NaCl stress

“…NaCl stress is a major global constraint to food production ( Naamala and Smith, 2021b ). Plant growth promoting microorganisms (PGPM), or their derived compounds have been reported to enhance plant growth under saline conditions ( Schwinghamer et al, 2016 ; Subramanian et al, 2016a , b ; Ilangumaran et al, 2021 ; Naamala et al, 2022 ). However, use of microbial CFS as plant growth biostimulants is less explored, with just a handful of publications available ( Tewari et al, 2020 ; Shah et al, 2022 ; Naamala et al, 2022 ).…”

“…Two NaCl levels, (100 mM NaCl and 150 mM NaCl) and two CFS levels (1.0 and 0.20% [v/v]) were used in the mixtures to formulate treatments. The two CFS concentrations were chosen because they exhibited positive results with Bacillus amyloliquefaciens EB2003 CFS, in our previous study ( Naamala et al, 2022 ). 0, 100 and 150 mM NaCl, with no addition of CFS were used as negative controls.…”

“…Recent studies have focused on the possibility that such metabolite rich media, also known as cell-free supernatant (CFS) can enhance plant growth without the presence of microbial cells. Experimentation with CFSs has previously yielded interesting results, showing that such CFSs can enhance the growth of different crop species, such as corn, soybean, canola and tomato, at germination and seedling stages ( Msimbira et al, 2022 ; Naamala et al, 2022 , Shah et al, 2022 ). Earlier studies went further and extracted bioactive compounds from the CFS, resulting in the discovery of compounds such as lipo-chitooligosaccharide (LCO) from Bradyrhizobium japonicum CFS and thuricin17 from Bacillus thuringiensis NEB17 CFS ( Prithiviraj et al, 2003 ; Gray et al, 2006a , b ; Lee et al, 2009 ), which are already on the market as plant growth promoting biostimulants.…”

“…Not all metabolites exuded in growth media enhance plant growth, although some are the bioactive ingredients that do so. The effectiveness of a bioactive metabolite/CFS also varies across plant species, concentration of the compound, level of stress to which a plant is exposed and growth stage of the plant ( Msimbira et al, 2022 ; Naamala et al, 2022 ; Shah et al, 2022 ). This, in a sense, complicates the process of discovering novel microbe derived plant growth promoting compounds as it may require trials on several crop species under different growth conditions, at different concentrations, before bioactivity may be detected.…”