Microbiology Editor’s Choice: zinc toxicity to marine micro-organisms

Posted on August 9, 2021   by Microbiology Society

Each month, a manuscript published in our flagship journal Microbiology  is chosen by a member of the Editorial Board. This month, the paper is titled ‘Investigating zinc toxicity responses in marine Prochlorococcus and Synechococcus’ and was chosen by Dr Martin Welch.  

Pollutants as a result of human activity, such as plastics, are a rich source of zinc ions. These can readily leach out of the polymer matrix and contaminate the local environment. Concentrations of zinc more than 150 mg L-1 have been reported in some aquatic environments, raising the question of whether such elevated zinc levels are toxic to the co-habiting microbes; an area of research that has received remarkably little attention to date.  

To redress this issue, Sarker and colleagues examined the impact of zinc on the growth of important marine photosynthetic picocyanobacteria such as Synechococcus sp. and Prochlorococcus sp. Building on earlier work showing that leachates from weathered plastic PVC matting is toxic to Prochlorococcus sp., these researchers showed that picocyanobacterial strains derived from marine environments display a remarkable degree of zinc-mediated inhibition of growth, with photosynthetic capacity and membrane integrity also impaired. This indicates that marine picocyanobacterial species have only limited mechanisms to cope with zinc toxicity, adding an additional (and previously unrecognised) layer of concern to the problem of anthropogenic insults in the marine environment.  

Investigating zinc toxicity responses in marine Prochlorococcus and Synechococcus 

Plastic pollution is a global and growing threat to marine ecosystems. Plastic litter leaches a variety of substances into the marine environment, with zinc, a common plastic additive, observed at particularly high levels in past plastic leachate studies. In this study, we set out to determine how representatives of an environmentally important group of marine photosynthetic microorganisms, picocyanobacteria, respond to exposure to elevated zinc levels that they might encounter near the increasing plastic waste. We found a range of zinc concentrations negatively affected photosynthetic health and cell membrane integrity of four distinct picocyanobacterial strains and show their different zinc sensitivities. 

We spoke with corresponding author Dr Sasha Tetu to find out more: 

What is your institution and how long have you been there?  

 I work at Macquarie University, in Sydney, Australia and have worked here for more than 10 years. 

What is your research area?   

My research looks at what kinds of microbes are present in different environments and what factors lead to certain microbes being more or less successful in a particular habitat. I also look at how environmental bacteria adapt to different pressures, including exposure to anthropogenic pollutants.   

What inspired you to research this topic?   

Marine pollution is a worldwide, growing issue that has the potential to impact key groups of bacterial primary producers that are critical to carbon cycling and the marine food web.  Past work in our lab showed that plastic pollution leaches a variety of substances that together adversely affect marine picocyanobacteria. As zinc was by far the most abundant inorganic component in these plastic leachates, we were interested in looking specifically at the impact of elevated zinc on picocyanobacteria. We hope these investigations will help highlight the need to consider the potential toxicity of common plastic additives in the assessment of plastic pollution risks. 

What is the most rewarding part of your research?  

I am inspired to tell the story of how critical bacteria are to good health not just in plants and animals, but to planet-wide processes.  Bacteria get a fair bit of bad publicity and to the public, they are considered mainly as disease-causing “germs”. Happily, this has started to change, and more people are learning about how bacteria can contribute to good health, due largely to interest in the gut microbiome. I hope to help extend this awareness of the usefulness of bacteria, highlighting how bacteria support ecosystem health on land and sea via key contributions to the food chain and nutrient cycling.  

What would you be doing if you weren't a scientist?  

I have asked myself this question increasingly frequently as universities in Australia shed staff at ever higher rates due to COVID-19-induced financial woes! I still haven’t come up with a great answer – I do love being able to investigate interesting research questions with the potential to add to our understanding of the world. Though it would be nice to have more time to hang out with my family at the beach... 

Follow authors Lisa Moore and Indrani Sarker on Twitter.