Evidence for a Functional Quorum-Sensing Type AI-1 System in the Extremophilic Bacterium Acidithiobacillus ferrooxidans

Abstract

Acidithiobacillus ferrooxidans is one of the main acidophilic chemolithotrophic bacteria involved in the bioleaching of metal sulfide ores. The bacterium-mineral interaction requires the development of biofilms, whose formation is regulated in many microorganisms by type AI-1 quorum sensing. Here, we report the existence and characterization of a functional type AI-1 quorum-sensing system in A. ferrooxidans. This microorganism produced mainly acyl-homoserine lactones (AHL) with medium and large acyl chains and different C-3 substitutions, including 3-hydroxy-C 8 -AHL, 3-hydroxy-C 10 -AHL, C 12 -AHL, 3-oxo-C 12 -AHL, 3-hydroxy-C 12 -AHL, C 14 -AHL, 3-oxo-C 14 -AHL, 3-hydroxy-C 14 -AHL, and 3-hydroxy-C 16 -AHL. A quorum-sensing genetic locus that includes two open reading frames, afeI and afeR, which have opposite orientations and code for proteins with high levels of similarity to members of the acyl synthase (I) and transcriptional regulator (R) protein families, respectively, was identified. Overexpression of AfeI in Escherichia coli and the associated synthesis of AHLs confirmed that AfeI is an AHL synthase. As determined by reverse transcription-PCR, the afeI and afeR genes were transcribed in A. ferrooxidans. The transcription levels of the afeI gene were higher in cells grown in sulfur and thiosulfate media than in iron-grown cells. Phosphate starvation induced an increase in the transcription levels of afeI which correlated with an increase in AHL levels. Two afe boxes which could correspond to the AfeR binding sites were identified upstream of the afeI gene. This is the first report of a functional type AI-1 quorum-sensing system in an acidophilic chemolithotrophic microorganism, and our results provide a very interesting opportunity to explore the control and regulation of biofilm formation during the bioleaching process.Quorum sensing (QS) is a widespread phenomenon that enables bacterial cells to establish cell-cell communication and to regulate the expression of specific genes in response to local changes in cell density (6,48,49). QS provides the means to coordinate the activities of cells so that they function as a multicellular unit and communicate with eukaryotic hosts (6,20,48,49). In gram-negative bacteria, depending on the autoinductor (AI) molecule, two QS processes have been described: type AI-1, which is involved mainly in intraspecies communication, and type AI-2, which is related to interspecies communication (20,49).The type AI-1 QS regulatory system is composed of four elements: (i) a transcriptional regulator (protein family R); (ii) a cis-acting DNA palindromic sequence; (iii) an acyl-homoserine lactone (AHL), which is the signaling molecule or autoinducer (AI-1); and (iv) the AHL synthase protein (protein family I), which synthesizes the AI (6,20,48,49). It is currently accepted that AI-1 diffuses freely between the cellular and external environments and complexes with the R protein only at a high cell density. The AHL-R complex binds through the R carboxyl domain to the specific site...

Control of Acetic Acid Fermentation by Quorum Sensing via N -Acylhomoserine Lactones in Gluconacetobacter intermedius

“…We designated the luxI and luxR homologues ginI and ginR, respectively, because of their functions in quorum sensing (see below). The primary sequence of GinI shares about 30% identity with diverse members of the LuxI family, including LuxI from Vibrio fischeri (3), AlpI from Azospirillum lipoferum (24), CepI from Burkholderia cepacia (11), and AfeI from Acidithiobacillus ferrooxidans (5). Similarly, GinR shares about 40% identity with several LuxR family members, including LuxR from V. fischeri (3), BpsR from Burkholderia pseudomallei (21), LuxR1 from Vibrio salmonicida (17), and AhyR from Aeromonus hydrophila (22).…”

Microbial Surface Colonization and Biofilm Development in Marine Environments

“…Interestingly, A. ferrooxidans harbors two QS systems (426). A Lux-like system is upregulated when A. ferrooxidans is grown in sulfur medium (427,428), while an Act-based system is upregulated when A. ferrooxidans is grown in medium containing iron instead of sulfur (426). Thus, it has been suggested that the two QS systems respond to different environmental signals that may be related to the abilities of A. ferrooxidans to colonize and use different solid sulfur-and ironcontaining minerals (426).…”

Isolation and Characterization of an Autoinducer Synthase from Acinetobacter baumannii

“…2). Interestingly, an open reading frame similar to A1S_0110 was present immediately upstream of putative autoinducer synthases from A. ferrooxidans (37% identity and 48% similarity) and Burkholderia pseudomallei (38% identity and 62% similarity) (9,33). Based on the 17989 genome, an open reading frame divergently transcribed from the A1S_0110 and abaI open reading frames was predicted to encode a LuxR protein designated AbaR (Fig.…”