The role of bacterial viruses in plant health

The role of bacterial viruses in plant health

We know how important bacteria and fungi are for the health of plants. In marine environments and in our own gut, bacteriophages (viruses that infect bacteria) are important in regulating the microbiome. Yet, their effect on bacteria living around the roots of plants has hardly been studied.

 'I cannot believe that they are not important,' says senior author of a review paper in Trends in Microbiology, which argues for more research into the role of bacteriophages in plant health.

Bacteria play an important role in many ecosystems. The possibility of large-scale DNA identification of microorganisms has revealed this over the past decade. But bacteria themselves are affected by bacteriophages, viruses that infect them. These phages can lyse the bacteria, which releases nutrients into the environment. On the other hand, the phages can live inside bacterial cells and affect their function. Finally, bacteriophages stimulate DNA transfer between cells and are known to have given cells new functionalities through this horizontal gene transfer.

'We know that soil bacteria are important for plants as well,' says the author. Soils are deserts with very little food, as most nutrients are present in complex forms that microorganisms cannot readily use. However, in the few millimetres of soil around plant roots, plants stimulate the growth of bacteria. Plants release carbon sources for the bacteria and the bacteria provide nutrients and protection for the roots. 'This creates an oasis called the rhizosphere,' explains the author.

Technical problems may also have affected studies into soil viruses, the author adds: 'We have the technology to identify viruses in ocean water and in our gut. Finding them in soil is quite a challenge.' It is relatively simple to filter virus particles from water but isolating them from a slurry is far more complicated. Salles suspects that this has led to bacteriophages being overlooked. 'There are just a handful of institutes where soil phages are being studied.'

Even bacteria can catch viruses. These viruses play an important role in nature. For example, they can change the number of certain bacterial species by killing bacteria, thereby freeing lots of nutrients or they can transfer DNA between cells. Bacterial viruses (also called bacteriophages) can play an important role in maintaining a healthy community of bacteria in our gut and can do the same in seawater. However, their role in soils is unclear. In a review article, the author argues that it is very likely that they are important for plant health: plants need bacteria around their roots to provide them with all kinds of nutrients and other compounds. Viruses will have an impact on these bacterial communities. Therefore, viruses are likely to be important for the health of plants.