Bioprospecting of extremophilic perchlorate-reducing bacteria: report of promising Bacillus spp. isolated from sediments of the bay of Cartagena, Colombia

Abstract

Three extremophile bacterial strains (BBCOL-009, BBCOL-014 and BBCOL-015), capable of degrading high concentrations of perchlorate at a range of pH (6.5 to 10.0), were isolated from Colombian Caribbean Coast sediments. Morphological features included Gram negative strain bacilli with sizes averaged of 1.75 × 0.95, 2.32 × 0.65 and 3.08 × 0.70 μm, respectively. The reported strains tolerate a wide range of pH (6.5 to 10.0); concentrations of NaCl (3.5 to 7.5% w/v) and KClO₄^- (250 to 10000 mg/L), reduction of KClO₄^- from 10 to 25%. LB broth with NaCl (3.5-30% w/v) and KClO4- (250-10000 mg/L) were used in independent trials to evaluate susceptibility to salinity and perchlorate, respectively. Isolates increased their biomass at 7.5 % (w/v) NaCl with optimal development at 3.5 % NaCl. Subsequently, ClO₄- reduction was assessed using LB medium with 3.5% NaCl and 10000 mg/L ClO₄-. BBCOL-009, BBCOL-014 and BBCOL-015 achieved 10%, 17%, and 25% reduction of ClO₄-, respectively. The 16 S rRNA gene sequence grouped them as Bacillus flexus T6186-2, Bacillus marisflavi TF-11 (T), and Bacillus vietnamensis 15 - 1 (T) respectively, with < 97.5% homology. In addition, antimicrobial resistance to ertapenem, vancomycine, amoxicillin clavulanate, penicillin, and erythromycin was present in all the isolates, indicating their high adaptability to stressful environments. The isolated strains from marine sediments in Cartagena Bay, Colombia are suitable candidates to reduce perchlorate contamination in different environments. Although the primary focus of the study of perchlorate-reducing and resistant bacteria is in the ecological and agricultural realms, from an astrobiological perspective, perchlorate-resistant bacteria serve as models for astrobiological investigations.

Keywords: Bioremediation; Halophytes; Marine sediment; RNA 16S.

Fig. 1

Map of Colombia’s Cartagena Bay indicates the sampling site’s location

Fig. 2

Neighbour-joining tree showing the phylogenetic positions of strains BBCOL-009, BBCOL-014 and BBCOL-015 with other closely related members based on 16 S rRNA gene sequences available from the EMBL database (accession numbers are given in parentheses). The topology of the entire tree was conserved in all trees using different algorithms. The bootstrap values, expressed as percentages at the branching points, indicate the confidence level of the tree branches and were calculated based on 1000 replications. Bar 0.01 nucleotide substitutions per nucleotide position

Fig. 3

Bacterial isolated from marine sediments. Morphology by SEM. a BBCOL-009, b BBCOL-014, c and BBCOL-015

Fig. 4

Percentage of KClO₄⁻ reduction of the bacteria BBCOL-009, BBCOL-014 and BBCOL-015 from saline environments in the sediments in Cartagena Bay. Effect of the 24 h contact time, optical density at OD 600, and optimal pH (7.0)