Selection of the N-Acylhomoserine Lactone-Degrading Bacterium Alteromonas stellipolaris PQQ-42 and of Its Potential for Biocontrol in Aquaculture

Abstract

The production of virulence factors by many pathogenic microorganisms depends on the intercellular communication system called quorum sensing, which involves the production and release of signal molecules known as autoinducers. Based on this, new-therapeutic strategies have emerged for the treatment of a variety of infections, such as the enzymatic degradation of signaling molecules, known as quorum quenching (QQ). In this study, we present the screening of QQ activity amongst 450 strains isolated from a bivalve hatchery in Granada (Spain), and the selection of the strain PQQ-42, which degrades a wide range of N-acylhomoserine lactones (AHLs). The selected strain, identified as Alteromonas stellipolaris, degraded the accumulation of AHLs and reduced the production of protease and chitinase and swimming motility of a Vibrio species in co-cultivation experiments in vitro. In the bio-control experiment, strain PQQ-42 significantly reduced the pathogenicity of Vibrio mediterranei VibC-Oc-097 upon the coral Oculina patagonica showing a lower degree of tissue damage (29.25 ± 14.63%) in its presence, compared to when the coral was infected with V. mediterranei VibC-Oc-097 alone (77.53 ± 13.22%). Our results suggest that this AHL-degrading bacterium may have biotechnological applications in aquaculture.

Keywords: N-acylhomoserine lactone; Vibrio; aquaculture; biocontrol; quorum quenching.

FIGURE 1

High-performance liquid chromatography plus mass-spectrometry analysis (HPLC-MS) measurements of C₆-HSL and C₁₀-HSL in the cell-free culture media of the N-acylhomoserine lactones (AHL)-degrading strain PQQ-42 after 24 h. Cell-free MB medium was used as negative control. Initial AHL concentration was 10 μM. Error bars represent one standard deviation.

FIGURE 2

Degrading activity by strain PQQ-42 of AHLs produced by pathogenic Vibrio spp. visualized on an agar plate assay by means of the biosensor strain Agrobacterium tumefaciens NTL4 (pZLR4). Cell-free MB medium added with Vibrio mediterranei VibC-Oc-097 AHL extracts (control; A). Culture of strain PQQ-42 added with V. mediterranei VibC-Oc-097 AHL extracts (B). Cell-free MB medium added with V. metschnikovii NCTC 8483^T AHL extracts (control; C). Culture of strain PQQ-42 added with V. metschnikovii NCTC 8483^T AHL extracts (D). Scale bar, 1 cm.

FIGURE 3

Oculina patagonica coral colonies after 10 day’s treatment showing the varying extent of bleaching depending on the bacterium added [1: Cell-free MB medium (control), 2: PQQ-42, 3: PQQ-42+V. mediterranei VibC-Oc-097, 4: V. mediterranei VibC-Oc-097]. Scale bar, 1 cm (A). Levels of chlorophyll a (B) and number of vibrios (CFU g^-1 C) in the tissue of O. patagonica after 5 and 10 day’s treatment. Error bars represent one standard deviation. Groups defined by post hoc SNK test after ANOVA (p-value < 0.05) were done and are showed by numbers.