Isolation, Preliminary Screening and Biochemical Characterization of Indigenous Crude Oil–Tolerant Bacteria from Contaminated Soil in Niger: Prospects for Bioremediation

Crude oil contamination of soil presents an environmental concern in Niger and creates a need to investigate indigenous microorganisms that can tolerate hydrocarbon exposure. This study isolated and preliminarily characterised bacteria from crude oil–contaminated soil collected at the Agadem oil field. Following preparation of a soil suspension, bacterial enrichment was conducted in Bushnell–Haas mineral medium, and morphologically distinct colonies were isolated and purified on Bushnell–Haas Agar supplemented with crude oil. Preliminary qualitative screening was undertaken on agar containing 1% (v/v) crude oil, with macroscopic changes examined after 24–72 hours of incubation. Bacterial growth was observed from the third day of initial incubation at 30 °C, and colony morphology varied in size, shape, colour and texture. Two selected isolates, BJ and BBC, were Gram-negative bacilli. Biochemical profiling using the VITEK 2 Compact system proposed the identification of isolate BJ as Aeromonas salmonicida with a probability of 94% and isolate BBC as Rhizobium radiobacter with a probability of 99%. These assignments remain provisional because they were based on an automated phenotypic method without molecular confirmation. The observed growth and changes in agar appearance indicated tolerance under the screening conditions but did not establish hydrocarbon biodegradation. The findings provide an initial description of indigenous bacterial isolates for subsequent taxonomic verification and quantitative assessment of their potential relevance to bioremediation.