Confirmation that candidatus Coxiella cheraxi from redclaw crayfish (Cherax quadricarinatus) is a close relative of Coxiella burnetii, the agent of Q-fever

A Coxiella sp. closely related to the agent of Q-fever, Coxiella burnetii, has been associated with mortalities in redclaw crayfish, (Cherax quadricarinatus), in farms and experimental facilities for three decades. Limited sequence data including 16S rRNA have placed the rickettsial species as a new species, candidatus C. cheraxi closely related to C. burnetii. MinION sequencing was conducted on the last remaining sample from an outbreak of disease, TO-98. The accuracy of base pair reads was mostly 99·9% (error rate 1 in 1000) or better. After filtering for reads of co-isolated Citrobacter freundii, 2629 sequences remained with the longest being 12 585 base pairs (bp). The longest 21 sequences are presented with their single best hit statistics when examined by NCBI blastn (nucleotides) and the nucleotides translated into proteins NCBI blastx. All sequences hit with either C. burnetii (29/42, 69%) or Coxiella (10/42, 24%) or rickettsia (3/42, 7%) with an error rate of less than 1 in 1 million for either bp or amino acids. Sequencing in this report confirms candidatus C. cheraxi is a new species very closely related to C. burnetii. SIGNIFICANCE AND IMPACT OF THE STUDY: This work reports on the use of newer technologies on archival samples and provides significantly more data on the currently limited genome data of candidatus Coxiella cheraxi, one of the few species isolated in the genus Coxiella. Candidatus Coxiella cheraxi causes death in redclaw crayfish and has been reported as being closely related to C. burnettii, the agent of Q-fever, based on 16S rRNA sequencing. This work provides confirmation for this claim.

Induction and characterization of lysogenic bacteriophages from Streptococcus iniae

AIMS

To investigate the presence of prophage in Streptococcus iniae, a highly problematic fish pathogen.

METHODS AND RESULTS

Cross-spotting assays and mitomycin C inductions were conducted to screen for prophage in 48 Strep. iniae isolates. Bacteriophages were characterized by plaque assays, transmission electron microscopy and DNA restriction enzyme digestion. Plaque assays confirmed prophages in 14·6% of isolates. Phages vB_SinS-44, vB_SinS-45, vB_SinS-46 and vB_SinS-48 lysed 78·5% of Strep. iniae isolates and displayed distinctive host ranges. Microscopy revealed virions exhibiting long, non-contractile tails and isometric heads consistent with phages from the family Siphoviridae. Restriction digests revealed genome sizes ranging from 27·5 to 66·3 kbp, with distinct cutting patterns that indicate the presence of related prophages in bacteria isolated from different geographic regions.

CONCLUSIONS

The rate of prophage carriage found is comparably low and induction rates varied between phages. The four characterized Siphoviridae phages have broad host ranges within the Strep. iniae isolates.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first description and characterization of lysogenic phages from Strep. iniae. These phages are candidates for research and diagnosis of the bacterium and their identification should accelerate the discovery of lytic phages to be trialled against Strep. iniae infections in fish.