Isolation and characterization of nitrogen-fixing bacteria from soil sample in Dhaka, Bangladesh

Biological nitrogen (N2) fixation is very essential for limiting the growth of plants and agricultural crops. The present study was conducted to potentially isolate N2-fixing bacteria from garden soil sample at Stamford University Bangladesh, Siddeswari, Dhaka. Here, we used culture-dependent method to perform this experiment. Firstly, we collected garden soil sample, diluted and inoculated in N2-free Jensen’s media by maintaining the aseptic procedure. We obtained 5 different colonies from soil samples. We cultured the isolates in N2-free Jensen’s media containing bromothymol blue (BMB) and also, in Yeast Extract Mannitol Agar (YEMA) media containing congo red to confirm nitrogen fixation capacity. We collected the colony characteristics of all the isolates. Only 1A isolate showed good growth after 24 h of incubation among all the isolates. We performed ammonification test with Nessler reagent to confirm N2-fixing ability for our selected isolates. The 1A isolate was positive in ammonification test. Culture, microscopy and biochemical tests were performed to identify isolate 1A. This isolate was presumptively identified as Azotobacter sp. In the present study, Azotobacter sp. that was isolated from the soil sample was found to be a potential N2-fixing bacterium. Isolate 1A can be used for N2-fixation to boost production of crops. Stamford Journal of Microbiology, Vol.11 (1) 2021: 11-13

Optical fiber mercury biosensor based on immobilized urease and bromothymol blue onto the alginate-chitosan membrane in the flow-system

An optical fiber biosensor has been developed for the detection of mercury ion based on inhibition of urease immobilized onto alginate–chitosan membrane, coupled with bromothymol blue (BTB) in the flow system. To get a good performance of the biosensor toward Hg(II) ion detection, the experimental parameters of the biosensor were optimized. Here, the maximum wavelength was detected at 580 nm, with the optimum response at pH of 6. The calibration curve had a dynamic working range at 10 to 500 μg/L of Hg(II) ion with a detection limit of 12.1 μg/L biosensor has been performed by the addition of 1 mM ethylenediaminetetraacetic acid (EDTA) solution, in which five-time cycles have been achieved with the inhibition decrease to 9.94% from the original biosensor response. Applying the biosensor to the real samples showed conformity of results with the reference method, cold vapor atomic absorption spectrometry (CV-AAS). Therefore, this biosensor can be used as a method for routine analysis in the determination of Hg(II) concentration in an aqueous sample.