• Question: Is there bacteria in a leaf?

    Asked by anon-44771 to Amelia, Clem, Izzy, Sarah on 18 Mar 2014.
    • Photo: Isabel Webb

      Isabel Webb answered on 18 Mar 2014:

      I don’t know of bacteria that live happily inside leaves. If a bacteria is inside a leaf, it is probably a disease that is invading the plant. The plant quickly responds by killing the leaf and letting it drop off before the bacteria spread.

      The leaf surface, however, is another story. Many bacteria call the leaf surface home – so much that we have a word for it! The ‘phyllosphere’ is the area on a leaf where micro-organisms can grow and survive. Of course, many of the bacteria on the leaf can also be disease-causing. They might even cause disease to humans – which is one of the reasons we wash salad really well before eating it. A research project I once did looked at the bacteria growing on leaf surfaces, and tried to find a way to kill any harmful E. coli bacteria that might be growing there.

    • Photo: Sarah Harvey

      Sarah Harvey answered on 18 Mar 2014:

      If there are bacteria in leaves, it’s likely that the plant is infected with something! They get infectious diseases just like we can, with bacteria often entering through stomata or wounds, like we breathe them in or get infected cuts. Plants can also get infected by viruses and fungi but they’re pretty good at defending themselves through a variety of different mechanisms. One genus of bacteria, Pseudomonas contains some species which are infection to plants and some that are infectious to humans although none which can infect both (maybe possible in the future I guess though!)

      You may have also heard of root nodules on some plants? Bacteria live in these and form what is called a symbiotic relationship with the plant as it helps both the bacteria and the plant; the bacteria have somewhere to live and the plant gets the aid of nitrogen fixing bacteria to provide nutrients.

    • Photo: Amelia Frizell-Armitage

      Amelia Frizell-Armitage answered on 19 Mar 2014:

      Yes there are hundreds of bacteria on leaves, both good and bad, the same way that your body is covered in bacteria. Not too sure about bacteria inside leaves- if there are bacteria there they are probably causing some sort of disease to the plant.

      The chloroplasts and mitochondria inside leaves actually used to be free living bacteria! Back when plants had not evolved yet and everything was just cells, the chloroplasts were bacteria that could photosynthesise and the mitochondria could respire. The chloroplasts and mitochondria joined forces with other cells that could not photosynthesise or respire, but could provide protection and food. As plants started to evolve the chloroplast and mitochondria continued to live happily inside the cells until eventually they never left and became part of the cell! They still have their own genes though, which is how we know they were once separate organisms.

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