Evidence for widespread microbivory of endophytic bacteria in roots of vascularplants through oxidative degradation in root cell periplasmic spaces

In this chapter we present a hypothesis, and data supporting it, that vascular plants in diverse families possess symbiotic/endophytic bacteria that frequently vector on or within their seeds; seedlings degrade symbiotic bacteria within roots. Evidence of widespread microbivory was found in a survey for intracellular bacteria that we conducted including seedlings in 36 species of vascular plants distributed in 20 plant families. Experiments indicate that when seeds germinate, bacteria colonize seedlings and internalize into root cells where they are oxidatively-degraded in the periplasmic spaces of cells. The process of degradation of microbes in roots has been termed “rhizophagy”, and “rhizophagy cycle” or “rhizophagy symbiosis” in the case of symbiotic bacteria that alternate between a free-living soil phase and intracellular/endophytic phase. We hypothesize that microbivory could account for a significant portion of nutrients acquired by plants from soils—with one estimate suggesting that as much as 30% of the nutrients acquired by seedlings may stem from rhizophagy symbiosis. Developing a better understanding of rhizophagy symbiosis could lead to new ways to cultivate crops without reliance on excessive agrochemical applications. Learning how to manipulate rhizophagy symbiosis could result in new technologies for reducing growth of weedy or invasive plant species by inhibiting rhizophagy symbiosis.