Public parks are a link to nature for city dwellers, but so far we know very little about what lurks within our green spaces on a microscopic level.

Recently, an international team of scientists mapped the microbiomes of public parks worldwide for the first time, including several parks in Pretoria, Johannesburg and Cape Town.

Professor Thulani Makhalanyane of UP's Centre for Microbial Ecology and Genomics, says their investigation unearthed a similar profile of park microbes across the world, as well as worrying levels of pathogens that are potentially dangerous to humans. They also found evidence of excessive greenhouse gas emissions.

Although the study only gives us some of the very first glimpses into the algae, amoeba and bacteria found in the world's public parks, Prof Makhalanyane says they would already recommend better management strategies for parks to reduce potentially harmful microbes present in the soil.

"We don't think this is something families visiting the park need to be worried about," says Prof Makhalanyane. "Public parks are still a very safe way to spend time outdoors, and the risk of exposure is extremely low; it is just something we'd like to raise to park managers to keep an eye on." 

Soil microbes form diverse ecosystems unseen beneath our feet at public parks. Many of these microbes are beneficial to the environment, but Prof Makhalanyane and his colleagues found genes belonging to soil Mycobacteria, known to cause respiratory infections in humans.

Their study also found high amounts of genes associated with listeria, diphtheria, and antibiotic resistance. "This high proportion of antibiotic-resistant genes within these soils might pose a problem for the health of the people that use these parks," says Prof Makhalanyane. In addition, the data seems to indicate that fertilisers allow these disease-causing microbes to thrive much more than they would in natural environments.

Greenhouse gases are another potential health risk commonly associated with urban environments. Still, researchers were surprised to find that public parks within cities might be contributing quite a bit to emissions. Prof Makhalanyane says they found high numbers of bacteria that thrive in mowed and well-irrigated park lawns, which produce high amounts of methane and nitrous oxide. 

For the South African part of the study, Prof Makhalanyane and his team did their sampling at urban parks, including the Magnolia Dell Park in Pretoria, Gillooly's Farm in Johannesburg, and Green Point Park in Cape Town. "We set up using standard protocols so that all the countries in the study collect samples the exact same way," he says.

If you happened to be out for a walk at one of these parks, you might have spotted Prof Makhalanyane and his team in a 30-by-30 metre grid collecting soil samples. "We also counted plants to see how their diversity changes over time because of different factors, and that tells us the most prevalent features that influence microbial diversity," he says.

The researchers compared each of the urban greenspace sample sites with nearby unmanaged natural areas away from the city and agricultural spaces to analyse the effects of park management practices. 

As expected, the study showed that similar microbial communities could be found in all these green spaces that all employed similar management practices. It also showed that factors like the local climate and the affluence of a city affect its microbial diversity.

For Prof Makhalanyane, this kind of research has a long way to go to be truly "global" as it only sampled parks in two African cities, both in South Africa. "You can imagine the types of insights that are lacking for Africa because there are only these two cities," he says.

The study, which recorded the microbiomes of 56 urban greenspaces in 17 countries, is just one of the many other similar global projects that Prof Makhalanyane is working on to map the earth's "microverse". It was recently published in the prestigious peer-reviewed journal, Science Advances, led by Professor Manuel Delgado-Baquerizo from Pablo de Olavide University (UPO) in Spain.