Symbiotic bacteria, immune-like sentinel cells, and the response to pathogens in a social amoeba

Abstract

Some endosymbionts living within a host must modulate their hosts' immune systems in order to infect and persist. We studied the effect of a bacterial endosymbiont on a facultatively multicellular social amoeba host. Aggregates of the amoeba Dictyostelium discoideum contain a subpopulation of sentinel cells that function akin to the immune systems of more conventional multicellular organisms. Sentinel cells sequester and discard toxins from D. discoideum aggregates and may play a central role in defence against pathogens. We measured the number and functionality of sentinel cells in aggregates of D. discoideum infected by bacterial endosymbionts in the genus Paraburkholderia . Infected D. discoideum produced fewer and less functional sentinel cells, suggesting that Paraburkholderia may interfere with its host's immune system. Despite impaired sentinel cells, however, infected D. discoideum were less sensitive to ethidium bromide toxicity, suggesting that Paraburkholderia may also have a protective effect on its host. By contrast, D. discoideum infected by Paraburkholderia did not show differences in their sensitivity to two non-symbiotic pathogens. Our results expand previous work on yet another aspect of the complicated relationship between D. discoideum and Paraburkholderia , which has considerable potential as a model for the study of symbiosis.

Complex third-party effects in theDictyostelium–Paraburkholderiasymbiosis: prey bacteria that are eaten, carried or left behind

“…Hosts in the absence of their Paraburkholderia symbionts are able to modify the contents of fruiting bodies through their immune cells that protect against toxins and bacteria by collecting potential threats and dropping-off during the slug stage [58]. However, the role of these immune cells in the symbiosis [59,60] needs to be further explored. Manipulation of phagosomes could also play a role in determining the contents of fruiting bodies.…”

Complex third-party effects in theDictyostelium-Paraburkholderiasymbiosis: prey bacteria that are eaten, carried, or left behind

“…Hosts in the absence of their Paraburkholderia symbionts are able to modify the contents of fruiting bodies through their immune cells that protect against toxins and bacteria by collecting potential threats and dropping off during the slug stage (Chen et al ., 2007). However, the role of these immune cells in the symbiosis (Brock et al ., 2016a; Scott et al ., 2023a) needs to be further explored. Manipulation of phagosomes could also play a role in determining the contents of fruiting bodies.…”

Unpredictable soil conditions can affect the prevalence of a microbial symbiosis

“…The source of this fitness cost for hosts is unknown, though there is some evidence that Paraburkholderia itself harms hosts. For example, the density of Paraburkholderia tends to be associated with lower host spore production ( Scott, Queller & Strassmann, 2022a , 2022b ; Noh et al, 2024 ) and Paraburkholderia infection interferes with host immune cells that develop during the multicellular stage ( Scott et al, 2023a ).…”