The Type II Secretion System Is Essential for Erythrocyte Lysis and Gut Colonization by the Leech Digestive Tract Symbiont Aeromonas veronii

Abstract

Hemolysin and the type II secretion system (T2SS) have been shown to be important for virulence in many pathogens, but very few studies have shown their importance in beneficial microbes. Here, we investigated the importance of the type II secretion pathway in the beneficial digestive-tract association of Aeromonas veronii and the medicinal leech Hirudo verbana and revealed a critical role for the hemolysis of erythrocytes. A mutant with a miniTn5 insertion in exeM, which is involved in forming the inner membrane platform in the T2SS, was isolated by screening mutants for loss of hemolysis on blood agar plates. A hemolysis assay was used to quantify the mutant's deficiency in lysing sheep erythrocytes and revealed a 99.9% decrease compared to the parent strain. The importance of the T2SS in the colonization of the symbiotic host was assessed. Colonization assays revealed that the T2SS is critical for initial colonization of the leech gut. The defect was tied to the loss of hemolysin production by performing a colonization assay with blood containing lysed erythrocytes. This restored the colonization defect in the mutant. Complementation of the mutant using the promoter region and exeMN revealed that the T2SS is responsible for secreting hemolysin into the extracellular space and that both the T2SS and hemolysin export by the T2SS are critical for initial establishment of A. veronii in the leech gut.

Aeromonas hydrophila and Aeromonas veronii Predominate among Potentially Pathogenic Ciprofloxacin- and Tetracycline-Resistant Aeromonas Isolates from Lake Erie

“…The regulation of these secretion systems is mediated via quorum sensing and may be associated with polar and lateral flagellar activity (45)(46)(47)(48). Type II secretion systems regulated by quorum sensing are involved in the secretion of multiple virulence factors, including serine protease and aerolysin (49,50).…”

Ciprofloxacin-Resistant Aeromonas hydrophila Cellulitis following Leech Therapy

“…Medicinal leeches (Hirudo medicinalis), used primarily in plastic and reconstructive surgeries to prevent venous congestion, maintain A. hydrophila, which is essential for the digestion of host erythrocytes, as an obligatory endosymbiont (4,5). Upon attachment to the skin, H. medicinalis bites the host and injects saliva that contains numerous anticoagulants and vasodilators to promote continuous blood supply during the leech blood meal (5,6).…”

Molecular Characterization of Fluoroquinolone-Resistant Aeromonas spp. Isolated from Imported Shrimp

“…Suarez et al delineated the importance of a T6SS effector protein, VgrG1, from A. hydrophila that induces host cell toxicity by ADP ribosylation of actin (26). Another study demonstrated the importance of T2SS in A. veronii (13). Results from our study indicate that the mutations in the gyrA and parC genes that are components of T3SS may play a vital role in increased cytotoxicity of the bacteria.…”