Sarcobium lyticum gen. nov., sp. nov., an Obligate Intracellular Bacterial Parasite of Small Free-Living Amoebae

Abstract

A new genus and species of obligate intracellular bacterial parasite of small free-living amoebae is described. This bacterium causes fatal infections in amoebae belonging to the Acanthamoeba-NaegZeria group. It does not grow on any artificial substrate deprived of living amoeba cells. The entry of the bacterium into a host occurs by phagocytosis, but growth occurs in the cytoplasm, not in phagosomes. This parasite is readily distinguished from other kinds of previously recognized bacteria that live within amoeba cells on the basis of its host cell lytic activity. The bacterium is a gram-negative, short rod with tapered ends. It multiplies intracellularly by a transverse central pinching-off process. Cells are motile by means of a polar tuft of flagella. The bacterium is surrounded by a distinct multilayered cell envelope with a chemtype A,y peptidoglycan. The peptidoglycan is unique in its high content of glucosamine residues with free amino groups. The DNA base composition of this organism is 43 mol% guanine plus cytosine. The name Sarcobium Zyticum gen. nov., sp. nov. is proposed for this bacterium. The type strain of S. Zyticum is strain L2 (= PCM 2298).More than 30 years ago a new obligate intracellular bacterial parasite (OIBP) which causes fatal infections of hosts was found in a raw culture of amoebae that were freshly isolated from soil (7). This OIBP was isolated from soil from the Lublin area, Poland. In previous reports I have described the infection processes for Acanthamoeba castellanii, Hartmannella rhysodes, Hartmannella astronyxis, Mayorella palestinensis, Didasculus thorntoni, Schizopyrenus ruselli, and Naegleria gruberii, as well as 41 other unclassified amoebae isolated from soil and water reservoirs (8, 10). The OIBP did not grow on any medium when living amoebae were not present. Even a thick suspension of disrupted amoeba cells was ineffective. It has been shown that the OIBP cannot multiply if after infection the mixed culture is heated at 43°C for 10 min; this treatment is sufficient to kill trophic forms of the amoeba, but the bacterium survives. Microscopy has shown (8,11). that the parasites are readily phagocytized by amoebae and that their immediate place of residence is within phagosomes. The neighboring phagosomes fuse extensively with parasite-containing vacuoles; however, even dead bacteria evade lysosoma1 attack because the cell wall is resistant to the host's bacteriolytic enzymes. Later, living bacteria escape from phagosomes into the cytoplasm, where multiplication occurs. The final effect of the infection is total lysis of the host cells. Although the morphology of the OIBP and the presence of peptidoglycan in its cell wall suggest that this organism is a bacterium, it has not been possible to classify it previously because of a lack of nutritional tests; the OIBP does not correspond to any bacterium described in Bergey's Manual of Determinative Bacteriology (3). Most of the many kinds of previously recognized bacteria that live within amoeba cells behave as temperate endos...

Phylogeny of Legionellaceae Based on Small-Subunit Ribosomal DNA Sequences and Proposal of Legionella lytica comb. nov. for Legionella-Like Amoebal Pathogens

“…The description of L. lytica comb. nov. is the same as that published for S. lyticum (17). Cells were gram negative and motile by means of three to five polar flagellar rods that were 0.6 X to 1.9 X lop6 m. The DNA base composition as determined by thermal denaturation was 43 mol% guanine plus cytosine.…”

“…[lo]) has precedent over Sarcobium (S. lyticum [17]) according to the Rule of Nomenclatural Priority (44), a proposal is made for the transfer of the species S. lyticum from the genus Sarcobium to Legionella as Legionella lytica (17) comb. nov.…”

Legionella drozanskii sp. nov., Legionella rowbothamii sp. nov. and Legionella fallonii sp. nov.: three unusual new Legionella species.

“…The only LLAP strain that has been validly named was classified in the absence of DNA homology data (Drozanski, 1991 ;Hookey et al, 1996). This strain was initially classified in a separate genus as Sarcobium lyticum, based on the phenotypic features of the organism and its obligate intracellular existence or pathogenicity for amoebae (Drozanski, 1991). However, S. lyticum was subsequently transferred to the genus Legionella as L. lytica, on the basis of 16S rRNA sequence analysis (Hookey et al, 1996).…”

“…Consequently, the characterization and classification of this interesting group of bacteria has been limited. The only LLAP strain that has been validly named was classified in the absence of DNA homology data (Drozanski, 1991 ;Hookey et al, 1996). This strain was initially classified in a separate genus as Sarcobium lyticum, based on the phenotypic features of the organism and its obligate intracellular existence or pathogenicity for amoebae (Drozanski, 1991).…”

Isolation, Identification and Increasing Importance of 'Free-Living' Amoebae Causing Human Disease

“…The presence of endosymbionts has been demonstrated in many protozoan species [57,[87][88][89][90]. The symbionts may either occur 'naturally' or may represent more recently phagocytosed organisms that have adapted to the intracellular environment.…”