Screening of Endophytic Bacteria from Azadirachta indica and Tridax procumbens for Waste-Engine-Oil-Associated Redox Activity: A DCPIP and Qualitative GC–MS Study
S. H. Kamble *
Department of Microbiology, D.B.F. Dayanand College of Arts and Science, Solapur, India.
A. Z. Durugkar
Department of Microbiology, D.B.F. Dayanand College of Arts and Science, Solapur, India.
V. S. Sangatekar
Department of Microbiology, D.B.F. Dayanand College of Arts and Science, Solapur, India.
K. S. Mudake
Department of Microbiology, D.B.F. Dayanand College of Arts and Science, Solapur, India.
*Author to whom correspondence should be addressed.
Abstract
Background: Plant-associated endophytic bacteria are a potential source of microorganisms exhibiting oxidative responses to petroleum-derived substrates, but screening assays alone do not establish the mass of oil removed.
Objective: To isolate bacterial endophytes from Azadirachta indica and Tridax procumbens, compare waste-engine-oil-associated redox responses, examine single-factor culture conditions, and describe qualitative gas chromatography–mass spectrometry (GC–MS) profiles.
Methods: Twelve bacterial isolates were recovered, of which two were selected for morphological and biochemical characterisation and screening with the redox dye 2,6-dichlorophenolindophenol (DCPIP). The selected isolates were examined on mineral-salt agar containing waste engine oil. Isolate I underwent 16S rRNA gene analysis and carbon-source, temperature, and pH comparisons; treated and untreated oil samples were examined by GC–MS.
Results: Within 72 h, the initial and final DCPIP absorbances were 0.332 and 0.047 for isolate I and 0.531 and 0.107 for isolate II, corresponding to unadjusted decreases in dye absorbance of 85.84% and 79.85%, respectively. These values are not percentages of oil degraded. Isolate I showed 99.86% sequence similarity to Kytococcus sedentarius. The single-factor tables ranked glucose, ambient incubation and pH 7 highest on the reported assay-response index. Comparative GC–MS peak lists showed differing relative profiles and tentative oxygenated-compound annotations, without demonstrating absolute compound loss or metabolic provenance. The final uninoculated-control value and assay-level replication were not documented, preventing attribution of these optical changes exclusively to oil-associated microbial metabolism.
Conclusion: The observations justify further testing of a neem-associated isolate closely related to K. sedentarius as a candidate for hydrocarbon-related microbial activity. The extent of waste-engine-oil biodegradation, mineralisation, and environmental effectiveness remains undetermined. The experiments are exploratory and do not establish statistically supported differences between isolates.
Keywords: Azadirachta indica, tridax procumbens, endophytic bacteria, kytococcus sedentarius, DCPIP assay, waste engine oil, GC–MS, preliminary screening