Isolation and characterization of a Pseudomonas putida strain able to growwith trimethyl-1,2-dihydroxy-propyl-ammonium as sole source of carbon, energy and nitrogen

Trimethyl-1,2-dihydroxypropyl-ammonium (TM) originates from the hydrolysis of the parent esterquat surfactant, which is widely used as softener in fab ric care. Based on test procedures mimicking complex biological systems, TM is supposed to degrade completely when reaching the environment. However, no organisms able to degrade TM were isolated nor has the degradation pathw ay been elucidated so far. We isolated a Gram-negative rod able to grow wit h TM as sole source of carbon, energy and nitrogen. The strain reached a ma ximum specific growth rate of 0.4 h(-1) when growing with TM as the sole so urce of carbon, energy and nitrogen. TM was degraded to completion and surp lus nitrogen was excreted as ammonium into the growth medium. A high percen tage of the carbon in TM (68% in continuous culture and 60% in batch cultur e) was combusted to CO2 resulting in a tow yield of 0.54 mg cell dry weight per mg carbon during continuous cultivation and 0.73 mg cell dry weight pe r mg carbon in batch cultures. Choline, a natural structurally related comp ound, served as a growth substrate, whereas a couple of similar other quate rnary aminoalcohols also used in softeners did not. The isolated bacterium was identified by 16S-rDNA sequencing as a strain of Pseudomonas putida wit h a difference of only one base pair to P. putida DSM. 291(T). Despite thei r high identity, the reference strain P. putida DSM 291(T) was not able to grow with TM and the two strains differed even in shape when growing on the same medium. This is the first microbial isolate able to degrade a quatern ary ammonium softener head group to completion. Previously described strain s growing on quaternary ammonium surfactants (decyltrimethyiammonium, hexad ecyltrimethylammonium and didecyldimethylammonium) either excreted metaboli tes or a consortium of bacteria was required for complete degradation.