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

Syazani Darham,Khalilah Abdul Khalil,Claudio Gomez-Fuentes,Suriana Sabri,Khadijah Nabilah Mohd Zahri,Siti Aqlima Ahmad,Peter Convey,Azham Zulkharnain

doi:10.3390/jmse9060648

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.

Highlights

Licensee MDPI, Basel, Switzerland.Heavy metal pollution is fast becoming a global threat
The bacterial culture was grown in saline nutrient broth (NB) with 5% (w/v) sodium chloride (NaCl) and maintained in 50% glycerol stock at −80 ◦ C
The study of microbial molybdate reduction to Mo-blue can contribute both to the advancement of bioremediation approaches and in developing understanding of microbial metal reduction

Summary

Introduction

Heavy metal pollution is fast becoming a global threat. Numerous industrial activities, including mining and smelting, are prime examples of anthropogenic sources of heavy metal discharge into the environment [1,2]. Rare heavy metals including molybdenum (Mo) have even been detected in the Antarctic [3,4,5]. Anthropogenic pollution sourced from nearby landmasses can reach the polar regions through long-range atmospheric transport and marine currents [6]. It has been suggested that mining sources in countries

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