Posts Tagged ‘symbiosis’
With the global population approaching seven billion and showing no sign of slowing, it’s not surprising that governments are worried about food security. A future without genetically modified crops now seems impossible.
In one of the more exciting genetic modification projects, scientists at the John Innes Centre in Norwich are trying to engineer wheat that can produce its own fertiliser. There is also growing interest in understanding the role of soils and soil microbes in promoting plant growth, and we’ve written before about the role of antibiotic-producing bacteria in disease-suppressive soils.
Two recent high-profile papers report a more detailed analysis of the microbiomes found in the roots and rhizosphere (the soil touching the roots) of the model weed Arabidopsis. Both studies found that the phylum Actinobacteria was one of the three most dominant groups in plant roots, and most of these were Streptomyces bacteria (streptomycetes).
Ants are amazing insects, and fungus-growing ants are perhaps the most amazing of all. This group includes the leafcutter ants that you’ve probably seen on David Attenborough’s TV programmes, carrying carefully cut leaf fragments to their nests along well-defined trails in the rainforest. Millions of ants can be found within a single underground nest the size of a three-storey house. Brilliantly, and without using a single moving part, the nests are perfectly air conditioned – maintaining constant temperature and humidity.
“But wait,” I hear you cry. “This is all very well, but what does it have to do with microbiology?” Well, did you ever wonder what the ants do with the leaves that they so diligently carry through the jungle? They don’t eat them; instead, they strip the waxy coating from the surface of the leaf and feed the mashed-up leaf material to a symbiotic fungus that they grow in ‘gardens’ found within the colony.
This fungus is the sole food source for their colonies and has co-evolved with the ants over 50 million years, during which it has developed structures rich in sugars and fats that the ants harvest to feed to their larvae and queen.
Symbiotic relationships, where organisms of different species work together for mutual gain, have been studied extensively in numerous biological systems, but modern genomic techniques are revolutionising our understanding of how these interactions work at the molecular level. A recent paper by John McCutcheon and Carol von Dohlen has reported an interesting case of a ‘three-way symbiosis’ between the mealybug (Planococcus citri) – a significant pest of plants – and two species of bacteria.
This interaction shows a high level of metabolic complementarity: the genes for several amino acid biosynthetic pathways that are essential to the mealybug are spread across the genomes of the three different species. This makes the mealybug completely dependent on its bacterial symbionts.