Search for Virulence Genes in [Serratia marcescens]: DNA Sequence Analysis of Two Candidate Genes

Serratia marcescens is a versatile bacterial species able to colonize a wide range of niches both terrrestrial and aquatic. It is a significant agent in nosocomial infections and recently identified as a major pathogen of elk horn corals in the Carribean. Searching for virulence genes that provide powerful molecular arsenals therefore provides invaluable information.

Two genes were targeted for isolation, sequencing and characterization, namely, the swrW and luxS genes from local M. marcescens isolates. The swrW gene is responsible for the synthesis of the biosurfactant serrawettin essential for population migration. The luxS gene on the other hand encodes an autoinducer important in quorum sensing for the synthesis of the red pigment prodigiosin.

The swrW sequence from four local isolates was amplified by PCR (PTC-100, MJ Research, Inc.) using primers SW2-F3 and SW2-R3 based sequences found in GenBank whereas primers for luxS were FluxS and RluxS also based on sequences found in GenBank. Sequencing was provided by MACROGEN (South Korea).

Multiple alignment of swrW sequences showed a concensus condensation domain characteristic of non-ribosomal protein synthesis. For the luxS alignment, high percent similarity was shown with the autoinducer-2 (AI-2) sequence involved in an alternative quorum sensing pathway.

The reported surfactant, antibiotic, and apoptotic properties among others, make swrW and luxS candidate virurence genes in M. marcescens. We await the sequences of a third and fourth gene to help solve the puzzle on broad host range and ecological niches exhibited by this species.