Detection of acylhomoserine lactones in cultures of Gluconacetobacter diazotrophicus PAL5

Abstract

Gluconacetobacter diazotrophicus is an acid-tolerant nitrogen- fixing Alphaproteobacterium first found in association with sugarcane. It has also been isolated from rice, coffee and tea, among others crops. The recent sequencing of the G. diazotrophicus PAL5 genome shows the presence of one luxI homolog. These genes encode LuxI-type enzymes responsible for the synthesis of N- acylhomoserine lactones (AHLs), the main quorum sensing molecules in gram negative bacteria. The objective of this work was the detection and identification of AHLs produced by G. diazotrophicus PAL5. The strain was cultured aerobically, and extracts were prepared with acidified ethyl acetate. Samples were analyzed by thin layer chromatography developed with the biosensor Agrobacterium tumefaciens NTL4 (pCF218) (pCF372). Results show that G. diazotrophicus PAL5 produce at least two types of AHLs under the assayed conditions. Short-chain AHLs could be detected since early exponential growth phase, and medium-chain AHLs were detected in mid- and late-exponential growth phase. The results suggest that the luxI homolog in G. diazotrophicus PAL5 is expressed and quorum sensing molecules are produced and secreted. Similar to other bacteria, production of AHLs in G. diazotrophicus PAL5 could serves as a signaling mechanism among members of this genus or as inter kingdom signals.