Gregarine apicomplexans – model organisms to uncover the evolutionary path to obligate intracellular parasitism?
Kevin McKinley, Emma Betts, Anastasios D. Tsaousis and Sonja Rueckert E very organism is supposed to be infected by at least one parasite in its lifetime. While we normally treat parasites as foes, could they actually be our friends? For most people in our society, it might sound odd that it could be beneficial to have a parasitic infection. Especially if we look at organisms that belong to the phylum Apicomplexa, a group described as obligate parasites. Included in this group are the causative agents of potentially fatal infectious diseases in humans such as malaria and toxoplasmosis. Nonetheless, scientists have shown that the presence of some apicomplexan species can have either no or beneficial effects on their hosts. This is especially true for the gregarine apicomplexans, which can be found on the whole spectrum of symbiosis from mutualism to parasitism. In this article, we are going to introduce gregarine apicomplexans and discuss how they can help us to understand the evolution of parasitism in this phylum. Gregarine apicomplexans Gregarines infect a broad range of freshwater, marine and terrestrial invertebrates, and some species have a wide geographic distribution. Most gregarines are host specific, but some species are capable of infecting multiple host organisms. What differentiates gregarines from other apicomplexans are stages within the gregarine life cycle that are only found within this group. There are around 1,800 gregarine species described from various hosts. Gregarines have been described from a fraction of existing invertebrates, leaving many to still be discovered. Gregarines belong to the class Conoidasida and are still often lumped into three major groups, the archigregarines, eugregarines and neogregarines, as the taxonomy is in steady flux. Neogregarines infect only terrestrial, primarily insect hosts and the majority of these hosts belong to the Diptera. Neogregarines can be found in their host’s fat bodies, haemocoel, Malpighian ducts and intestines. Archigregarines
88 Microbiology Today October 2022 | microbiologysociety.org
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