The birds, the bees and the bacteria

Spring has arrived. The warm sun, colourful flowers and delightful springtime fragrances stir us from our winter sleep. And not only plants and animals but humans, too, are more actively courting one another during this time of year. But did you know that microbes play a vital role in this spring fever?

Nature in bloom

The quintessential image of the Netherlands: bulb fields filled with tulips, daffodils and hyacinths. Without microbes, however, these fields would be considerably less colourful. A wide variety of bacteria and fungi live in the vicinity of the roots of every plant, collectively known as the rhizosphere. They help the plant absorb the required nutrients and protect against pathogens. A plant cannot grow – let alone bloom – without these microbes.

The 750,000 flower bulbs at ARTIS could not bloom without microbes.

Something for everyone

Over 92% of the plant families work with mychorrhizal fungi. Other plants have bacterial companions. For example, papilionaceous flowers work with bacteria of the Rhizobium genus. They ‘infect’ the root, causing a kind of benign tumour to grow. These root nodules are the ideal locations for bacteria to take in nitrogen from the air for the plant in exchange for sugars.

Rhizobium bacteria live in root nodules in papilionaceous flowers where they take in nitrogen for the plant in exchange for sugars

Spring fragrances

In addition to the gorgeous colours, spring has a highly recognisable palette of fragrances, too. As soon as the first spring sun rays reach the earth, it immediately smells like spring. The spring fragrances are created by bacteria including Streptomyces. These soil bacteria produce a compound called geosmin (Greek for ‘earthy-smelling’). When the bacteria die, the compound is released. As a volatile compound, it evaporates as soon as the ground heats up. Which predominantly occurs in spring, of course. Cyanobacteria in ponds and ditches – better known as ‘blue-green algae’ – also produce this compound. In other words, the smells that define spring actually come from the microbes around us.

A colony of soil bacteria (Streptomyces) produce the earthy forest smell that characterises spring so strongly.

Evolved preference

Humans are extremely sensitive to geosmin. We can smell it in concentrations of less than 0.7 parts geosmin per billion (ppb). For most substances this is approximately 100 ppb. Our affinity with geosmin likely dates back centuries. The Streptomyces and cyanobacteria tend to live in damp places, making geosmin a good indicator for water. It helps to be able to smell that. Although we humans do not really need this trait nowadays, there are other animals that do. For example, camels are able to detect a water source in the desert from more than 75 kilometres away.

Camels use the geosmin produced by bacteria to be able to smell a water source from more than 75 kilometres away.

Spring fever

Spring also brings spring fever. All creatures, including humans, are looking for a suitable partner. Every human has a symbiotic relationship with some hundred-thousand billion micro-organisms, collectively known as the microbiome. These microbes protect you against pathogens, for example, and produce vitamins and hormones. Some 99% of these microbes are found in your intestines. Your intestinal microbes not only have a major impact on your health but also affect your mood, self-confidence, emotions and social interactions. Anyone who believes our choice of partner is entirely one of personal choice is in for a surprise. To a large extent, your microbes determine who you fall in love with.

The billions of microbes on your body keep you healthy and influence your behaviour.

In love thanks to your microbes

They mainly exert this influence through body odour. Our body odour plays an important and for the most part unconscious role in the choice of partner. In mammals (which includes humans), body odour is determined by the smell of sweat. Sweat itself has no odour; it is the skin bacteria living in our sweat glands that make it smell. One of the compounds added by these bacteria is AND, which causes a strong reaction in the part of the brain that is key for sexual arousal.

The composition of our sweat bacteria and therefore our body odour is different for everyone. Studies show that we subconsciously choose a bodily odour that is complementary to ours. In other words, we choose a partner with a different bacterial composition, ensuring our offspring will have a more diverse and therefore healthier microbiome.

Body odour mainly comes from the bacteria that live in our sweat glands and is an important unconscious factor in partner choice.

This and that

Plants and animals are not the only ones busy with reproduction in spring. Microbes join in, too. Over the past 3.7 billion years, microbes have found all sorts of unique methods for multiplying. They are the experts when it comes to reproduction. Faster, more numerous and in more ways than you can imagine. Would you like to witness a live birth? Or do you want to find out how many eggs the water bear lays? Attend ‘The Lab Technician Explains’ talk in Micropia this spring.   

The water bear lays her eggs in her moulted exoskeleton. Would you like to know more? Attend the special ‘The Lab Technician Explains’ talk in Micropia this spring.