ICP-MS analysis of metal and metalloid concentrations of common microbiological growth media reveals presence of heavy metals

Abstract

Trace elements such as cobalt and manganese play important roles as cofactors of enzymes, and thus, they collectively impact on biochemistry and cellular metabolism. Hence, it is of importance to gain an understanding of the trace metal and metalloid concentrations of growth medium in order to fully account for the growth performance of the bacterium. But, this aspect of microbial cell cultivation is usually neglected. Advent of instrumented techniques for metals and metalloid analysis such as inductively coupled plasma mass spectrometry (ICP-MS) has significantly facilitated trace element analysis at the parts per billion (ppb) to parts per million (ppm) level in aqueous matrixes free of organic interference. In this work, ICP-MS was utilized as the principal tool for profiling the range of metals and metalloids in different microbiological growth medium ranging from minimal salts medium to complex chemically undefined medium. Growth media examined include: LB Lennox, LB Lennox + 2 g/L glucose, LB Lennox (buffered, 89 mM phosphate), LB Lennox (buffered, 89 mM phosphate) + 6 g/L glucose, formulated medium + 6 g/L glucose, Tryptic Soy Broth, M9 medium, and M9 + 1 g/L yeast extract medium. Results reveal detection of elevated concentrations of chromium, copper and cadmium in different versions of LB Lennox and Tryptic Soy Broth. Concentrations of the above heavy metals in the tens of ppm range meant that the growth media could only support the growth of environmental bacteria with some resistance to heavy metal toxicity. On the other hand, no heavy metals were detected in M9 minimal salts medium or a modified version with supplementation of 1 g/L yeast extract. This indicated that minimal salts media may have less of a problem with heavy metal contamination compared to chemically undefined microbiological growth media. Collectively, the results highlight the essentiality of conducting a comprehensive profiling experiment for detecting different metals and metalloids at trace levels in microbiological growth medium. Such data would in addition to offering a deeper understanding of some peculiar growth behaviour from some microorganisms, may also help identify contamination issue during manufacture that preclude use of the media in cultivating many laboratory domesticated microorganisms. Subject areasbiochemistry, biotechnology, cell biology, microbiology, biochemical engineering,