Molecular Characterization of “Candidatus Parilichlamydia carangidicola,” a Novel Chlamydia-Like Epitheliocystis Agent in Yellowtail Kingfish, Seriola lalandi (Valenciennes), and the Proposal of a New Family, “Candidatus Parilichlamydiaceae” fam. nov. (Order Chlamydiales)
ABSTRACT
Three cohorts of farmed yellowtail kingfish (
Seriola lalandi
) from South Australia were examined for
Chlamydia
-like organisms associated with epitheliocystis. To characterize the bacteria, 38 gill samples were processed for histopathology, electron microscopy, and 16S rRNA amplification, sequencing, and phylogenetic analysis. Microscopically, the presence of membrane-enclosed cysts was observed within the gill lamellae. Also observed was hyperplasia of the epithelial cells with cytoplasmic vacuolization and fusion of the gill lamellae. Transmission electron microscopy revealed morphological features of the reticulate and intermediate bodies typical of members of the order
Chlamydiales
. A novel 1,393-bp 16S chlamydial rRNA sequence was amplified from gill DNA extracted from fish in all cohorts over a 3-year period that corresponded to the 16S rRNA sequence amplified directly from laser-dissected cysts. This sequence was only 87% similar to the reported “
Candidatus
Piscichlamydia salmonis” (AY462244) from Atlantic salmon and Arctic charr. Phylogenetic analysis of this sequence against 35
Chlamydia
and
Chlamydia
-like bacteria revealed that this novel bacterium belongs to an undescribed family lineage in the order
Chlamydiales
. Based on these observations, we propose this bacterium of yellowtail kingfish be known as “
Candidatus
Parilichlamydia carangidicola” and that the new family be known as “
Candidatus
Parilichlamydiaceae.”