AhlX, an N-acylhomoserine Lactonase with Unique Properties

Efficacy of ceftiofur N-acyl homoserine lactonase niosome in the treatment of multi-resistant Klebsiella pneumoniae in broilers

In this study, the efficiency of the ceftiofur N-acyl homoserine lactonase niosome against multi-resistant Klebsiella pneumoniae in broilers was evaluated. Fifty-six K. pneumoniae isolates previously recovered from different poultry and environmental samples were screened for the ahlK gene. The lactonase enzyme was extracted from eight quorum-quenching isolates. The niosome was formulated, characterized, and tested for minimal inhibitory concentration (MIC) and cytotoxicity. Fourteen-day-old chicks were assigned to six groups: groups Ӏ and П served as negative and positive controls, receiving saline and K. pneumoniae solutions, respectively. In groups Ш and IV, ceftiofur and niosome were administrated intramuscularly at a dose of 10 mg/kg body weight for five consecutive days, while groups V and VI received the injections following the K. pneumoniae challenge. Signs, mortality, and gross lesions were recorded. Tracheal swabs were collected from groups П, V, and VI for counting K. pneumoniae. Pharmacokinetic parameters were evaluated in four treated groups at nine-time points. The niosome was spherical and 56.5 ± 4.41 nm in size. The viability of Vero cells was unaffected up to 5 × MIC (2.4 gml-1). The niosome-treated challenged group showed mild signs and lesions with lower mortality and colony count than the positive control group. The maximum ceftiofur serum concentrations in treated groups were observed 2 h following administration. The elimination half-life in niosome-treated groups was longer than that reported in ceftiofur-treated groups. This is the first report of the administration of N-acyl homoserine lactonase for the control of multi-resistant K. pneumoniae infections in poultry.

N-acylhomoserine lactonase-based hybrid nanoflowers: a novel and practical strategy to control plant bacterial diseases

BACKGROUND

The disease caused by plant pathogenic bacteria in the production, transportation, and storage of many crops has brought huge losses to agricultural production. N-acylhomoserine lactonases (AHLases) can quench quorum-sensing (QS) by hydrolyzing acylhomoserine lactones (AHLs), which makes them the promising candidates for controlling infections of QS-dependent pathogenic bacteria. Although many AHLases have been isolated and considered as a potentially effective preventive and therapeutic agents for bacterial diseases, the intrinsically poor ambient stability has seriously restricted its application.

RESULTS

Herein, we showed that a spheroid enzyme-based hybrid nanoflower (EHNF), AhlX@Ni₃(PO₄)₂, can be easily synthesized, and it exhibited 10 times AHL (3OC8-HSL) degradation activity than that with free AhlX (a thermostable AHL lactonase). In addition, it showed intriguing stability even at the working concentration, and retained ~ 100% activity after incubation at room temperature (25 °C) for 40 days and approximately 80% activity after incubation at 60 °C for 48 h. Furthermore, it exhibited better organic solvent tolerance and long-term stability in a complicated ecological environment than that of AhlX. To reduce the cost and streamline production processes, CSA@Ni₃(PO₄)₂, which was assembled from the crude supernatants of AhlX and Ni₃(PO₄)₂, was synthesized. Both AhlX@Ni₃(PO₄)₂ and CSA@Ni₃(PO₄)₂ efficiently attenuated pathogenic bacterial infection.

CONCLUSIONS

In this study, we have developed N-acylhomoserine lactonase-based hybrid nanoflowers as a novel and efficient biocontrol reagent with significant control effect, outstanding environmental adaptability and tolerance. It was expected to overcome the bottlenecks of poor stability and limited environmental tolerance that have existed for over two decades and pioneered the practical application of EHNFs in the field of biological control.

Mining marine metagenomes revealed a quorum-quenching lactonase with improved biochemical properties that inhibits the food spoilage bacteria Pseudomonas fluorescens

The marine environment presents great potential as a source of microorganisms that possess novel enzymes with unique activities and biochemical properties. Examples of such are the quorum-quenching (QQ) enzymes that hydrolyze bacterial quorum-sensing (QS) signaling molecules, such as N-acyl-homoserine lactones (AHLs). QS is a form of cell-to-cell communication that enables bacteria to synchronize gene expression in correlation with population density. Searching marine metagenomes for sequences homologous to an AHL lactonase from the phosphotriesterase-like lactonase (PLL) family, we identified new putative AHL lactonases (sharing 30-40% amino acid identity to a thermostable PLL member). Phylogenetic analysis indicated that these putative AHL lactonases comprise a new clade of marine enzymes in the PLL family. Following recombinant expression and purification, we verified the AHL lactonase activity for one of these proteins, named marine originated Lactonase Related Protein (moLRP). This enzyme presented greater activity and stability at a broad range of temperatures and pH, and tolerance to high salinity levels (up to 5M NaCl), as well as higher durability in bacterial culture, compared to another PLL member. The addition of purified moLRP to cultures of Pseudomonas fluorescens inhibited its extracellular protease activity, expression of the protease encoding gene, biofilm formation, and the sedimentation process in milk-based medium. These findings suggest that moLRP is adapted to the marine environment, and can potentially serve as an effective QQ enzyme, inhibiting the QS process in gram-negative bacteria involved in food spoilage. Importance Our results emphasize the potential of sequence and structure-based identification of new quorum-quenching (QQ) enzymes from environmental metagenomes, such as from the ocean, with improved stability or activity. The findings also suggest that purified QQ enzymes can present new strategies against food spoilage, in addition to their recognized involvement in inhibiting bacterial pathogen virulence factors. Future studies on the delivery and safety of enzymatic QQ strategy against bacterial food spoilage should be performed.