Isolation and identification of high fluoride resistant bacteria from water samples of Dindigul district, Tamil Nadu, South India

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 β 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.