Shewanella khirikhana sp. nov. – a shrimp pathogen isolated from a cultivation pond exhibiting early mortality syndrome

Abstract

Summary Early mortality syndrome (EMS) in cultivated shrimp is of complex aetiology. One of the causes is acute hepatopancreatic necrosis disease (AHPND) caused by unique Vibrio isolates that carry two Pirvp toxin genes, but other causes of EMS remain mostly unexplained. Here, we describe the discovery of a Shewanella isolate TH2012T from an EMS/AHPND outbreak pond and demonstrate its virulence for shrimp (the mean lethal concentration of 105 colony‐forming units per millilitre by immersion challenge) accompanied by distinctive histopathology, particularly of the ventral nerve cord and lymphoid organ but also including the digestive tract. On the basis of its complete genome sequence, multilocus phylogenetic trees, digital DNA–DNA hybridization analysis and differential phenotypic characteristics, we propose that Shewanella isolate TH2012T represents a novel species, separated sufficiently from the type strains S. litorisediminis and S. amazonensis to justify naming it Shewanella khirikhana sp. nov. Analysis of the TH2012T genome revealed no homologues of the Pirvp toxin genes but revealed a number of other potential virulence factors. It constitutes the first Shewanella isolate reported to be pathogenic to shrimp.

Acute Hepatopancreatic Necrosis Disease (AHPND): Virulence, Pathogenesis and Mitigation Strategies in Shrimp Aquaculture

“…( Shewanella sp.) [ 41 , 43 , 50 , 52 ]. These processes explain the huge possibility of conversion from non-pathogenic to pathogenic AHPND strain that positively enhance the spread of AHPND [ 42 ].…”

Carbon sources improve water quality, microbial community, immune‐related and antioxidant genes expression and survival of challenged Litopenaeus vannamei Postlarvae in biofloc system

“…The disease is highly contagious and fatal and caused mortality of over 50% of L. vannamei in China in 2017 (Cao et al, 2018). In another study, an immersion challenge with Shewanella khirikhana caused severe mortality in shrimp (Prachumwat et al, 2020). Our challenge assay revealed that BFT protects shrimp from disease as biofloc treatments had a minor mortality rate compared with the control treatments with the lowest mortality in the SCB treatment.…”

“…All tanks were well‐aerated, and the temperature was kept at 27–28°C. The challenge test was performed by injecting the bacterial suspension into water 1.96 × 10 7 cfu/ml for the Vibrio challenge according to Lin et al (2013) and 1.5 × 10 6 cfu/ml for the Shewanella challenge according to Prachumwat et al (2020). The mortality rate of the shrimp was monitored daily for 10 days, and any dead shrimp were immediately excluded from the glass tanks.…”

Shewanella cyperi sp. nov., a facultative anaerobic bacterium isolated from mangrove sediment

“…In the phylogenomic tree, strains FJAT-53720 T and FJAT-53726 clustered with the members of the genus Shewanella Table 1. Differential physiological and biochemical characteristics of strains FJAT-53720 T , FJAT-53726 and its closely related species Strains: 1, FJAT-53720 T (data from this study); 2, FJAT-53726 (data from this study); 3, Shewanella algae JCM 21037 T (data from this study); 4) Shewanella khirikhana TH2012 T (data from reference [35]). +, Positive; −, negative.…”