Why should we care? Well, to better understand cause and effect relationships in nature, we need to be aware of all the components that are playing a role. For example, imagine if there was such a scenario where the flu virus actually infected and resided within helpful bacteria that lived in our lungs, and not us directly (and the cause of sickness were due to the death of these bacteria). If this imaginary flu-carrying bacterium turned out to be unable to survive on skin and other common surfaces but ultra-resilient as an airborne pathogen, then our whole idea of flu transmission would be wrong, and health policy would need be reformed; people would be far less concerned with washing their hands and sanitizing surfaces, and would start wearing masks. To take full advantage of our surroundings, we need to fully understand our surroundings.
Such may be the case with the Tomato yellow leaf curl virus (TYLCV). As its name might suggest, the acquisition of this disease by tomatoes causes a curling/shriveling of the leaf, a yellow discoloration, stunting of plant growth, and more (2), and can result in complete loss of tomato crop; this, consequently, leads to disastrous economical impacts. In a study by Su et al., it was found that the incidence of TYLCV infection correlated strongly with the presence of a bacterial symbiont of whitefly Bemisia tabaci. B. tabaci is known to transmit this virus, but what we did not know previously is that symbiont Hamiltonella is likely responsible for its intense transmission.