Statistical Modeling for the Optimization of Bioluminescence Production by Newly Isolated Photobacterium sp. NAA-MIE

Comparison of Joint Effect of Acute and Chronic Toxicity for Combined Assessment of Heavy Metals on Photobacterium sp.NAA-MIE

Predicting the crucial effect of single metal pollutants against the aquatic ecosystem has been highly debatable for decades. However, dealing with complex metal mixtures management in toxicological studies creates a challenge, as heavy metals may evoke greater toxicity on interactions with other constituents rather than individually low acting concentrations. Moreover, the toxicity mechanisms are different between short term and long term exposure of the metal toxicant. In this study, acute and chronic toxicity based on luminescence inhibition assay using newly isolated Photobacterium sp.NAA-MIE as the indicator are presented. Photobacterium sp.NAA-MIE was exposed to the mixture at a predetermined ratio of 1:1. TU (Toxicity Unit) and MTI (Mixture Toxic Index) approach presented the mixture toxicity of Hg²⁺ + Ag⁺, Hg²⁺ + Cu²⁺, Ag⁺ + Cu²⁺, Hg²⁺ + Ag⁺ + Cu²⁺, and Cd²⁺ + Cu²⁺ showed antagonistic effect over acute and chronic test. Binary mixture of Cu²⁺ + Zn²⁺ was observed to show additive effect at acute test and antagonistic effect at chronic test while mixture of Ni²⁺ + Zn²⁺ showing antagonistic effect during acute test and synergistic effect during chronic test. Thus, the strain is suitable and their use as bioassay to predict the risk assessment of heavy metal under acute toxicity without abandoning the advantage of chronic toxicity extrapolation.

Rapid assessment of heavy metal toxicity using bioluminescent bacteria Photobacterium leiognathi strain GoMGm1

Several commercial test kits such as Microtox, LUMIStox, ToxAlert, Aboatox, and ToxScreen have been widely used for toxicity screening. Though this time saving assays offer excellent sensitivity, cost-effectiveness, and accuracy, these commercial assays are limited in terms of real-time monitoring in Indian coastal environment due to warmer temperatures. This necessitates the need to develop a rapid and accurate assay that can be effectively employed for real time monitoring with respect to heavy metals in the Indian coastal waters. With this objective, the present study was conducted by isolating an indigenous luminescent bacterium from the light organs of chordates Gazza minuta which showed higher luminescence in a wide range of temperatures. The isolate could grow well in the temperature of 30 ± 2 °C and withstand temperature up to 35 ± 2 °C. The isolated bacterium was identified as Photobacterium leiognathi GoMGm1 based on 16S rDNA and luxA gene sequences. The suitable growing medium was optimized using central composite rotational design (CCRD) method to obtain optimal growth and luminescence. The optimized medium exemplified the maximal growth and luminescence of P. leiognathi at OD_{600 nm} of 5.78 ± 0.12 and RLU of 12.49 ± 0.43. The isolate was used to assess the toxicity of several heavy metals. The IC₅₀ values of 0.0051, 1.13, 1.37, 3.1, and 6.68 mg L^-1 were observed for the Hg, Cr, Cu, Ni, and Zn, respectively, after 15 min of exposure. Results obtained from principal component analysis (PCA) displayed the present assay's compatibility with other luminescent bacterial assay and commercial Microtox™ assay. Thus, it would the right candidate as an early detection system for heavy metals in aquatic bodies in tropical countries. Schematic representation of the present study.