Browsing by Author "TAHZIBUL ISLAM DIHAN"

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    ISOLATION AND CHARACTERIZATION OF CHROMIUM-TOLERANT BACTERIA FROM POULTRY EXCRETA
    (2025-12-15) TAHZIBUL ISLAM DIHAN
    Chromium (Cr) contamination represents a critical environmental challenge in Bangladesh, largely driven by the integration of tannery byproducts into poultry feed. This study aimed to isolate and characterize chromium- tolerant bacteria from poultry excreta to assess their potential for environmental bioremediation. Initial screening was conducted on Luria-Bertani (LB) agar enriched with 100 mg/L of potassium dichromate (K2Cr2O7). Five high-tolerance strains (ID-01, ID-09, ID-10, ID-11, and ID-14) were selected based on their growth performance across a concentration range of 100–500 mg/L over a 34-h period. The Cr (VI) reduction efficiency of these isolates was subsequently assayed using the 1,5-diphenylcarbazide colorimetric method. Among the isolates, ID-14 exhibited the highest reduction potential, reducing 98.17% of Cr(VI) at 100 mg/L, though efficiency decreased to 48.12% at 500 mg/L concentration. Biochemical characterization and antibiotic susceptibility testing (Kirby–Bauer method) assessed phenotypic traits and potential resistance co-selection, revealing multidrug-resistant phenotypes, notably in isolate ID-14 which exhibited the most extensive resistance profile, including Ampicillin, Levofloxacin, Ceftazidime & Oxacillin etc. Molecular identification of three top-performing isolates was achieved through 16S rRNA gene sequencing, which revealed that ID-11 matched with Proteus mirabilis, ID-10 with Staphylococcus xylosus & ID-09 with Staphylococcus cohnii. However, the most tolerant strain, ID-14, underwent Whole Genome Sequencing (WGS) to map the genetic architecture of its resistance determinants. WGS revealed that the isolate was Staphylococcus ureilyticus. Genomic analysis identified multiple metal resistance determinants, including chromium resistance genes such as chrA and cysk, which encode chromium efflux and reductive mechanisms, respectively. In addition, genomic mapping uncovered diverse antibiotic resistance genes (ARGs), including the fluoroquinolone resistance genes norA, norB, beta-lactam antibiotic resistance genes blaZ, fmtA, macrolide resistance genes mphC & msrA and multidrug resistance genes emrB & sdrM. Overall, these results identify potential indigenous bacterial candidates capable of mitigating heavy metal pollution and provide essential baseline genomic data for bioremediation strategies.