Tributyl phosphate biodegradation to butanol and phosphate and utilization by a novel bacterial isolate, Sphingobium sp. strain RSMS

Abstract

A Sphingobium sp. strain isolated from radioactive solid waste management site (RSMS) completely degraded 7.98 g/L of tributyl phosphate (TBP) from TBP containing suspensions in 3 days. It also completely degraded 20 mM dibutyl phosphate (DBP) within 2 days. The strain tolerated high levels of TBP and showed excellent stability with respect to TBP degradation over several repeated subcultures. On solid minimal media or Luria Bertani media supplemented with TBP, the RSMS strain showed a clear zone of TBP degradation around the colony. Gas chromatography and spectrophotometry analyses identified DBP as the intermediate and butanol and phosphate as the products of TBP biodegradation. The RSMS strain utilized both TBP and DBP as the sole source of carbon and phosphorous for its growth. The butanol released was completely utilized by the strain as a carbon source thereby leaving no toxic residue in the medium. Degradation of TBP or DBP was found to be suppressed by high concentration of glucose which also inhibited TBP or DBP dependent growth. The results highlight the potential of Sphingobium sp. strain RSMS for bioremediation of TBP and for further molecular investigation.

Involvement of phosphoesterases in tributyl phosphate degradation in Sphingobium sp. strain RSMS

“…Sphingobium strains were grown in the modified mineral medium (hereafter referred to as MMM) (Rangu et al 2014), supplemented with either 1 % glucose and 5 mM KH 2 PO 4 , or 20 mM DBP, or a specified amount of TBP, as the sole source of carbon and phosphorous. The strains were either grown on solid MMM agar (MMMA) or Luria Bertani agar (LBA) (1.5 % w/v) or in liquid MMM at 30°C under continuous shaking (180 rpm).…”

“…The strains were either grown on solid MMM agar (MMMA) or Luria Bertani agar (LBA) (1.5 % w/v) or in liquid MMM at 30°C under continuous shaking (180 rpm). Since TBP is sparingly soluble in water (<1.5 mM), the concentration of added TBP is described as BTBP equivalent^and specified as BmM e^, which is the concentration that would be attained, when the added TBP is completely dissolved (Rangu et al 2014). The wild type Sphingobium sp.…”

“…The cultures were incubated at 30°C at 180 rpm for 24 h. TBP/DBP degradation was assessed spectrophotometrically by measuring the phosphate released in the medium by the phosphomolybdic acid method (Ames 1966). TBP/DBP and their degradation products and intermediates were also estimated by gas chromatography, in combination with spectrophotometry, as described earlier (Rangu et al 2014). …”

“…In the past three decades, several bacterial strains, displaying varying TBP-degrading abilities, have been reported (Ahire et al 2012;Berne et al 2004Berne et al , 2005Chaudhari et al 2012;Kulkarni et al 2014;Rangu et al 2014;Rosenberg and Alexander 1979;Thomas and Macaskie 1996). Among these, the Sphingobium sp.…”

“…strain RSMS (deposited at Microbial Type Culture Collection and Gene Bank, Chandigarh, India (http://mtcc.imtech.res.in) under the accession number 11630) showed the highest efficiency of TBP degradation, utilized TBP as well as DBP as the sole source of carbon and phosphorous and tolerated high levels of TBP (Rangu et al 2014). The biochemical pathway for the TBP degradation was revealed in Sphingobium strain RSMS and involved conversion of TBP to DBP as an intermediate and then to butanol and inorganic phosphate as the end products (Rangu et al 2014). However, the molecular basis of TBP/DBP degradation remains enigmatic.…”