A purified lipase from the yeast Cryptococcus sp. strain S-2 exhibited remote homology to proteins belonging to the cutinase family rather than to lipases. This enzyme could effectively degrade the high-molecular-weight compound polylactic acid, as well as other biodegradable plastics, including polybutylene succinate, poly (-caprolactone), and poly(3-hydroxybutyrate).Polylactic acid (PLA) is a plastic obtained from renewable resources that has attracted attention in response to increasing concerns about the environmental effects of disposal of nonbiodegradable plastics (4). However, the infrastructure for the disposal of biodegradable waste plastics is still not complete (4). Enzymatic degradation is an ideal waste treatment method because enzymes accelerate hydrolysis of PLA and other biodegradable plastics and can be incorporated into a natural cycle of organic materials. Furthermore, the hydrolysate can be recycled as material for polymers. Degradation of low-molecular-weight PLA has been investigated with lipase from Rhizopus delemer (3) and polyurethane esterase from Comamonas acidovorans TB-35 (1). Attempts to degrade PLA with other enzymes have resulted in only modest success (12,19). Studies on the degradation of high-molecular-weight PLA have been performed with strains of Amycalotopsis sp. (7, 13). However, the enzymes secreted by these microorganisms were not identified.The yeast Cryptococcus sp. strain S-2 isolated in our laboratory could be used for various wastewater treatment processes (6), and it produced a lipase (8) which could be used effectively in the production of methyl esters, which were excellent substitutes for diesel fuel (9). In the present study, the purified lipase from Cryptococcus sp. strain S-2 was analyzed to determine its amino acid sequence, and it was compared with lipases and other related enzymes in the database. An attempt was made to test the potency of the purified enzyme for the degradation of high-molecular-weight PLA and other biodegradable plastics. The enzyme was produced and purified as described previously (8). The purified enzyme produced a single band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis gels.Nucleotide sequencing. The open reading frame encoding the enzyme contains 720 nucleotides, including a start codon (ATG) and a stop codon (TAA). N-terminal sequencing of the purified mature protein revealed that the first 34 amino acids are a secretion signal sequence. The deduced amino acid sequence of the mature protein contains 205 amino acids with an estimated molecular mass of 20.9 kDa, which was similar to the molecular mass estimated from sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the purified protein (8).A BLAST search revealed that the deduced amino acid sequence of this protein did not exhibit homology with any of the known lipases, and the enzyme was found to be weakly (12 to 20%) homologous to proteins belonging to the cutinase family. Alignment of sequences around putative catalytic residues in known cutinases and thi...
We have developed a number of broad-host-range plasmids that allow the expression of the Escherichia coli lac operon from any cloned promoter, and the creation of 'in phase' fusions between lacZ and other cloned genes. In a second series of constructions, the E. coli gal operon has been cloned into the broad-host-range vector and a plasmid carrying both the E. coli gal and lac genes is described. These plasmids have been transferred into Pseudomonas aeruginosa and Zymomonas mobilis and their effects on the utilisation of lactose and galactose have been investigated.
Biodegradable plastics (BPs) have attracted much attention since more than a decade because they can easily be degraded by microorganisms in the environment. The development of aliphatic-aromatic co-polyesters has combined excellent mechanical properties with biodegradability and an ideal replacement for the conventional nondegradable thermoplastics. The microorganisms degrading these polyesters are widely distributed in various environments. Although various aliphatic, aromatic, and aliphatic-aromatic co-polyester-degrading microorganisms and their enzymes have been studied and characterized, there are still many groups of microorganisms and enzymes with varying properties awaiting various applications. In this review, we have reported some new microorganisms and their enzymes which could degrade various aliphatic, aromatic, as well as aliphatic-aromatic co-polyesters like poly(butylene succinate) (PBS), poly(butylene succinate)-co-(butylene adipate) (PBSA), poly(ε-caprolactone) (PCL), poly(ethylene succinate) (PES), poly(L-lactic acid) (PLA), poly(3-hydroxybutyrate) and poly(3-hydoxybutyrate-co-3-hydroxyvalterate) (PHB/PHBV), poly(ethylene terephthalate) (PET), poly(butylene terephthalate) (PBT), poly(butylene adipate-co-terephthalate (PBAT), poly(butylene succinate-co-terephthalate) (PBST), and poly(butylene succinate/terephthalate/isophthalate)-co-(lactate) (PBSTIL). The mechanism of degradation of aliphatic as well as aliphatic-aromatic co-polyesters has also been discussed. The degradation ability of microorganisms against various polyesters might be useful for the treatment and recycling of biodegradable wastes or bioremediation of the polyester-contaminated environments.
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