Evaluation of Plant Growth-promoting Properties of Nitrogen-Fixing Enterobacter mori Strain P5 (MW242734.1) isolated from Spent Mushroom Substrates

Abstract

negatively owing to the toxic residues emanating from repeated chemical fertilizer application. The evaluation of spent

mushroom substrate (SMS) as a source of plant growth promoting bacteria is considered a safe alternative to chemical

fertilizers. Mannitol Ashby selective agar and semi solid bromthymol blue agar without nitrogen were used to isolate

nitrogen-fixing bacteria and screen bacterial isolates for nitrogen fixation potentials respectively. Bergey’s Systematic

Bacteriology manual was used for initial identification. Secondary bacterial metabolites were quantified using standard

microbiological methods. Seven isolates (C1 to C7) were confirmed to fix atmospheric nitrogen. Colony forms and edges

of all isolates were all circular and entire respectively. Only C3 and C6 showed gray colony colours whereas other colonies

were white. Isolates C2 and C3 gave high ammonia production and nitrogen fixing efficiency. Each isolate showed varying

concentrations of all the secondary metabolites examined. Isolate C3 had significant peak indole acetic acid (IAA)

production (300 ± 12.8mg/L), gibberellins (410 ± 15.0 mg/L), 1-aminocyclopropane-1-carboxylate (ACC) deaminase

secretion (3.07 ± 0.3 mg/mg protein) and hydrogen cyanide production (0.15 ± 0.007 mg/L). Isolate C3 was identified

molecularly as Enterobacter mori strain P5 (MW242734.1) with 99.7% similarity. SMS can be considered as a better

alternative to chemical fertilizer since they harbor diversity of bacteria species beneficial to plants such as Enterobacter

mori strain P5 that is also environmentally friendly.