Statistical Optimisation and Kinetic Studies of Molybdenum Reduction Using a Psychrotolerant Marine Bacteria Isolated from Antarctica

Abstract

The extensive industrial use of the heavy metal molybdenum (Mo) has led to an emerging global pollution with its traces that can even be found in Antarctica. In response, a reduction process that transforms hexamolybdate (Mo6+) to a less toxic compound, Mo-blue, using microorganisms provides a sustainable remediation approach. The aim of this study was to investigate the reduction of Mo by a psychrotolerant Antarctic marine bacterium, Marinomonas sp. strain AQ5-A9. Mo reduction was optimised using One-Factor-At-a-Time (OFAT) and Response Surface Methodology (RSM). Subsequently, Mo reduction kinetics were further studied. OFAT results showed that maximum Mo reduction occurred in culture media conditions of pH 6.0 and 50 ppt salinity at 15 °C, with initial sucrose, nitrogen and molybdate concentrations of 2.0%, 3.0 g/L and 10 mM, respectively. Further optimization using RSM identified improved optimum conditions of pH 6.0 and 47 ppt salinity at 16 °C, with initial sucrose, nitrogen and molybdate concentrations of 1.8%, 2.25 g/L and 16 mM, respectively. Investigation of the kinetics of Mo reduction revealed Aiba as the best-fitting model. The calculated Aiba coefficient of maximum Mo reduction rate (µmax) was 0.067 h−1. The data obtained support the potential use of marine bacteria in the bioremediation of Mo.

Optimisation of Various Physicochemical Variables Affecting Molybdenum Bioremediation Using Antarctic Bacterium, Arthrobacter sp. Strain AQ5-05

“…RSM is a tool that explores the interaction between each parameter affecting the Mo-reducing ability of Arthrobacter sp. strain AQ5-05 by running sequential sets of experiment [17]. In this part of the study, Box-Wilson central composite design (CCD) was implemented to screen the variables using Design-Expert Version 6.0.8 (Stat-Ease Inc., Minneapolis, MN, USA).…”

“…Pure culture of the strain was maintained in 80% glycerol and stored in −80 • C freezer in Eco-Remediation Technology Laboratory, Faculty of Biotechnology and Biomolecular Sciences, Universiti Putra Malaysia. [17]. The media and glucose were separately autoclaved at 121 • C for 15 min.…”

“…strain AQ5-13, and Ba sp. strain A.rzi demonstrated that these bacteria work best in (NH4)2SO4 [17,[23][24][25] In the Mo reduction metabolic pathway, simple carbohydrates are preferred as electron donors as they can produce reducing equivalents for NADH and NADPH and are the substrates for Mo-reducing enzymes [20,21]. A few mesophilic bacterial strains such as Bacillus sp.…”

“…In comparison with a study by Ahmad et al [7] using Pseudomonas sp. strain DRY1 isolated from Antarctic soil, glucose was the best electron donor, while Darham et al [17] reported that Mo-reducing Antarctic marine bacterium Marinomonas sp. strain AQ5-A9 favour sucrose, thereby reflecting a simple growth-associated process of the species.…”

“…AQ5-05 in reducing Mo and to generate the most effective condition for Mo reduction via OFAT approach. Conditions such as pH, temperature, types of electron donor, and salinity have been reported to affect the efficiency of Mo reduction [8,17]. This study also investigates the relationship between the physicochemical variables for a more efficient Mo reduction via RSM approach.…”