Cutinolytic esterase activity of bacteria isolated from mixed-plant compost and characterization of a cutinase gene from Pseudomonas pseudoalcaligenes

The objective of the current study was to examine cutinolytic esterase (i.e., cutinase) activity by pseudomonads and bacteria isolated from mixed-plant compost. Approximately 400 isolates representing 52 taxa recovered from mixed-plant compost using cuticle baits, along with 117 pseudomonad isolates obtained from a culture collection (i.e., non-compost habitats), were evaluated. The ability of isolates to degrade the synthetic cutin polycaprolactone (PCL) was initially measured. Isolates from 23 taxa recovered from the compost degraded PCL. As well, isolates from 13 taxa of pseudomonads cleared PCL. Secondary screening measured esterase activity induced by the presence of apple cuticle using the chromogenic substrate p-nitrophenyl butyrate. Eighteen isolates representing four taxa (Alcaligenes faecalis, Bacillus licheniformis, Bacillus pumilus, and Pseudomonas pseudoalcaligenes) recovered from compost exhibited substantial esterase activity when grown with cuticle. In contrast, none of the pseudomonad isolates from the culture collection produced appreciable esterase activity. Although degradation of PCL was not correlated with esterase activity, isolates that were unable to degrade PCL failed to produce measureable esterase activities. Zymogram analysis indicated that the esterases produced by bacteria from compost ranged in size from 29 to 47 kDa. A gene from P. pseudoalcaligenes (cutA) was found to code for a cutin-induced esterase consisting of 302 amino acids and a theoretical protein size of 32 kDa. The enzyme was unique and was most closely related to other bacterial lipases (<= 48% similarity).