Studies on degradation efficiency of polycaprolactone by a naturally-occurring bacterium.

ABSTRACT

We report a strain of Bacillus, isolated from the rhizosphere of the mangrove Sesuvium portulacastrum, that degrades polycaprolactone (PCL) on timescales that are a factor of three shorter than hitherto reported, with complete degradation in only 20 days. The bacterium has been identified as Bacillus pumilus by means of 16S rRNA gene sequencing and FAME analysis; it secretes proteases and lipases and its ‘de-polymerase’ activity is evident by the zone of clearing in emulsified PCL. It is an aerobic chemoheterotroph capable of utilizing a variety of carbohydrates. Although not a true psychrophile, is a mesophile, growing optimally over a temperature range 30-45° C and pH range 5-12.5. It is a halophile tolerating NaCl concentrations up to 10% w/v, and is unique in degrading and utilizing PCL and its monomer, e-caprolactone (CL), as a sole carbon source. Degradation of PCL was monitored using Fourier Transform Infrared (FTIR) spectroscopy, light microscopy and scanning electron microscopy (SEM). This degradation was found to be enhanced by salts (NaCl, KCl, MgSO4, Na2HPO4) and at medium pH values in excess of 7. Under the same growth conditions, another standard Bacillus pumilus strain showed somewhat reduced PCL-degradation.