RESUMEN
Fluoride (F - ) pollution is one of the major issues in India and worldwide. Water samples were collected, and analyse the physicochemical characteristics. From the results, acceptable limit pH ranges, low and high electrical conductivity (EC) values, high-level of TDS (total dissolved solids) and chloride (Cl-) values, less than desirable and higher than permissible F - concentrations (4.7 and 11 ppm) were found. At first, ninety-three colonies were screened using rapid hicoliform agar plates. After that, sixty-six F - resistant colonies were picked up from 50 mM NaF (Sodium fluoride) containing LB agar plates. Finally, eight isolates were showing a high degree of F - resistance (200--300 mM NaF) and selected for further studies. High F - resistance isolates exhibited ß and γ-haemolytic activities were determined in blood agar plates. F - resistant isolates showed their salt tolerances ranged from 4% to 7% NaCl and resistant to multiple antibiotics. Biochemical and 16S rRNA sequencing results showed that the F - resistant isolates were identified as Enterobacter cloacae strain 3, E. hormaechei strain 14, Enterobacter sp. strain 21, E. hormaechei strain 22, E. coli strain S2-9, Aeromonas caviae strain 31, A. caviae strain 32, A. caviae strain 34. All strains were submitted in the NCBI database with the accession numbers (MW131637, MW131639; MW131650-655). The F - resistant gene 'crcB' gene was successfully amplified from the resistant isolates using gene-specific primers. These results have demonstrated that fluoride resistant bacteria would be useful for bacterial fluoride bioremediation near future.
RESUMEN
In our previous study, all Pseudomonas strains THP6, THP41, and OHP5 were identified as fluoride-resistant bacteria isolated from Dindigul district, Tamilnadu, India. The selected strains exhibiting a high level of fluoride resistance was determined in Luria broth (LB) medium and LB agar plates. In a further effort, fluoride-resistant organisms were tested for hemolytic activity and showed ß-hemolysis on blood agar plates. The virulence factors such as gyrB, toxA, algD and lasB, plcH, rhlC and biofilm response genes (pslA, pelA, ppyR) were detected by PCR analysis. The putative genus-specific and species-specific PCR also confirmed that the selected fluoride-resistant strains were belonging to Pseudomonas aeruginosa species. Fluoride-resistance gene crcB was amplified by gene-specific primers. The crcB gene was cloned in TA vector and transformed into E. coli DH5α. Comparative and blast analysis of THP6, THP41, and OHP5 strains crcB gene sequences were high homology with P. aeruginosa fluoride efflux transporter crcB and P. aeruginosa putative fluoride ion transporter crcB. The recombinants were efficiently growing in the NaF containing LB agar plates. The fluoride tolerance of these strains was also associated with resistance to multiple antibiotics. These results can lead to the use of the fluoride resistance gene of P. aeruginosa for the development of a biosensor for fluoride detection.