Phylogenetic analysis of the pathogenic bacteria Spiroplasma penaei based on multilocus sequence analysis

Area of Science:

• Aquatic microbiology
• Marine invertebrate pathology
• Bacterial genomics

Background:

• Emerging infectious diseases pose significant threats to global aquaculture.
• Pacific white shrimp (Penaeus vannamei) aquaculture is vital but susceptible to pathogens.
• Spiroplasma species are known insect pathogens, but their role in crustaceans is less understood.

Purpose of the Study:

• To identify and characterize a novel Spiroplasma strain isolated from diseased Penaeus vannamei.
• To determine the phylogenetic origin and evolutionary relationships of the new Spiroplasma strain.
• To describe the clinical presentation and implications of this emerging crustacean disease.

Main Methods:

• Isolation and identification of the bacterial pathogen from moribund shrimp hemolymph.
• Multilocus phylogenetic analysis using partial and complete DNA sequences of ribosomal and housekeeping genes (16S rDNA, 23S rDNA, 5S rDNA, gyrB, rpoB).
• Phylogenetic trees reconstructed using the Neighbor-Joining (NJ) method with Kimura-2-parameter model.

Main Results:

• A pathogenic Spiroplasma penaei strain was successfully isolated from Penaeus vannamei exhibiting high mortality.
• Phylogenetic analyses placed S. penaei within the Citri-Poulsonii clade, closely related to Spiroplasma insolitum.
• Evidence suggests a terrestrial origin for the S. penaei strain, distinct from other known shrimp-associated Spiroplasma.

Conclusions:

• Spiroplasma penaei represents a novel emerging pathogen causing systemic infection in marine shrimp.
• The terrestrial origin of S. penaei has significant implications for disease prevention and biosecurity in shrimp farming.
• Further research is needed to understand the transmission dynamics and full impact of S. penaei on crustacean aquaculture.