Ciliates Expel Environmental Legionella-Laden Pellets To Stockpile Food

Abstract

f When Tetrahymena ciliates are cultured with Legionella pneumophila, the ciliates expel bacteria packaged in free spherical pellets. Why the ciliates expel these pellets remains unclear. Hence, we determined the optimal conditions for pellet expulsion and assessed whether pellet expulsion contributes to the maintenance of growth and the survival of ciliates. When incubated with environmental L. pneumophila, the ciliates expelled the pellets maximally at 2 days after infection. Heat-killed bacteria failed to produce pellets from ciliates, and there was no obvious difference in pellet production among the ciliates or bacterial strains. Morphological studies assessing lipid accumulation showed that pellets contained tightly packed bacteria with rapid lipid accumulation and were composed of the layers of membranes; bacterial culturability in the pellets rapidly decreased, in contrast to what was seen in ciliate-free culture, although the bacteria maintained membrane integrity in the pellets. Furthermore, ciliates newly cultured with pellets were maintained and grew vigorously compared with those without pellets. In contrast, a human L. pneumophila isolate killed ciliates 7 days postinfection in a Dot/Icm-dependent manner, and pellets harboring this strain did not support ciliate growth. Also, pellets harboring the human isolate were resuscitated by coculturing with amoebae, depending on Dot/Icm expression. Thus, while ciliates expel pellet-packaged environmental L. pneumophila for stockpiling food, the pellets packaging the human isolate are harmful to ciliate survival, which may be of clinical significance.

Current and Emerging Legionella Diagnostics for Laboratory and Outbreak Investigations

“…However, it soon became clear that the unique physiology of legionellae was primarily adapted for survival and replication within numerous protozoan genera, including Acanthamoeba, Naegleria, Hartmannella, and Tetrahymena (24,53,54), and secondarily as a freeliving or biofilm-associated aquatic bacterium. Their association with amoebae, in the vegetative or cyst form, may induce virulent bacterial phenotypes, assist in distribution, and provide protection from harsh or bactericidal environmental conditions, such as excessive heat and chlorine (55)(56)(57)(58)(59)(60)(61)(62)(63)(64)(65).…”

Identification of Aeromonas hydrophila Genes Preferentially Expressed after Phagocytosis by Tetrahymena and Involvement of Methionine Sulfoxide Reductases

“…Once preyed by protozoa, most microbes are digested as food, but some microbes appear to be resistant to protozoa digestion and can even replicate within protozoa. Several bacterial pathogens, including E. coli (King et al, 1988), L. pneumophila (Berk et al, 2008; Hojo et al, 2012), S. enterica (Brandl et al, 2005; Rehfuss et al, 2011), and Listeria monocytogenes (Pushkareva and Ermolaeva, 2010), have been shown to be resistant to destruction in digestive vacuoles of Tetrahymena . In this study, we observed that T. thermophila fed readily on A. hydrophila strains, however, LSCM and TEM observations and the survival rate of A. hydrophila in vacuoles indicated that the virulent strains were able to survive in T. thermophila vacuoles.…”

“…King et al (1988) reported that many bacterial pathogens can resist the grazing protozoan Tetrahymena pyriformis . After predation by Tetrahymena species, Legionella pneumophila (Berk et al, 2008; Hojo et al, 2012) and Salmonella enterica (Brandl et al, 2005) are released in a viable form in vesicles or pellets from the protozoa. Due to the presence of a membrane around the vesicle, the bacterial cells within the vesicles are more resistant to disinfectants than those remaining free in suspension (Brandl et al, 2005).…”

Protozoal ciliate promotes bacterial autoinducer-2 accumulation in mixed culture with <i>Escherichia coli</i>

“…While such a microbiota plays a fundamental role in feeding bacteria as a nutrient source for predators such as ciliates or amoebae, the bacteria presumably exploit the microbiota for nutrient-rich environments to ensure survival (Russell and Rychlik, 2001;Tyson et al, Protozoal ciliate promotes bacterial autoinducer-2 accumulation in mixed culture with Escherichia coli (Received June 29, 2015;Accepted July 27, 2015) Satoshi Oguri, 1,3 Tomoko Hanawa, 2 Junji Matsuo, 3 Kasumi Ishida, 3 Tomohiro Yamazaki, 3,5 Shinji Nakamura, 4 Torahiko Okubo, 3 Tatsuya Fukumoto, 1 Kouzi Akizawa, 2004), and the acquisition of virulence factors or resistance against unpredictable harmful conditions through gene exchange (Aminov, 2011). Highly packed bacteria, such as in biofilms or ciliate vacuoles, are directly responsible for phenotypic features, possibly with genetic exchanges, against harmful environmental conditions, and also evoke quorum sensing via autoinducer (AI)-2 production (Aminov, 2011;Hojo et al, 2012;Lang and Faure, 2014). We have previously found that a mixed culture of Escherichia coli with Tetrahymena ciliates could prove beneficial in gene exchange between the bacteria (Matsuo et al, 2010;Oguri et al, 2011).…”