Characterization of a novel lipase and its specific foldase from Acinetobacter sp. XMZ-26

Biodegradation of Oil by a Newly Isolated Strain Acinetobacter junii WCO-9 and Its Comparative Pan-Genome Analysis

Waste oil pollution and the treatment of oily waste present a challenge, and the exploitation of microbial resources is a safe and efficient method to resolve these problems. Lipase-producing microorganisms can directly degrade waste oil and promote the degradation of oily waste and, therefore, have very significant research and application value. The isolation of efficient oil-degrading strains is of great practical significance in research into microbial remediation in oil-contaminated environments and for the enrichment of the microbial lipase resource library. In this study, Acinetobacter junii WCO-9, an efficient oil-degrading bacterium, was isolated from an oil-contaminated soil using olive oil as the sole carbon source, and its enzyme activity of ρ-nitrophenyl decanoate (ρ-NPD) decomposition was 3000 U/L. The WCO-9 strain could degrade a variety of edible oils, and its degradation capability was significantly better than that of the control strain, A junii ATCC 17908. Comparative pan-genome and lipid degradation pathway analyses indicated that A. junii isolated from the same environment shared a similar set of core genes and that the species accumulated more specific genes that facilitated resistance to environmental stresses under different environmental conditions. WCO-9 has accumulated a complete set of oil metabolism genes under a long-term oil-contamination environment, and the compact arrangement of abundant lipase and lipase chaperones has further strengthened the ability of the strain to survive in such environments. This is the main reason why WCO-9 is able to degrade oil significantly more effectively than ATCC 17908. In addition, WCO-9 possesses a specific lipase that is not found in homologous strains. In summary, A. junii WCO-9, with a complete triglyceride degradation pathway and the specific lipase gene, has great potential in environmental remediation and lipase for industry.

Biophysical characterization of a recombinant lipase KV1 from Acinetobacter haemolyticus in relation to pH and temperature

Spectroscopic and calorimetric methods were employed to assess the stability and the folding aspect of a novel recombinant alkaline-stable lipase KV1 from Acinetobacter haemolyticus under varying pH and temperature. Data on far ultraviolet-circular dichroism of recombinant lipase KV1 under two alkaline conditions (pH 8.0 and 12.0) at 40 °C reveal strong negative ellipticities at 208, 217, 222 nm, implying its secondary structure belonging to a α + β class with 47.3 and 39.0% ellipticity, respectively. Results demonstrate that lipase KV1 adopts its most stable conformation at pH 8.0 and 40 °C. Conversely, the protein assumes a random coil structure at pH 4.0 and 80 °C, evident from a strong negative peak at ∼ 200 nm. This blue shift suggests a general decline in enzyme activity in conjunction with the partially or fully unfolded state that invariably exposed more hydrophobic surfaces of the lipase protein. The maximum emission at ∼335 nm for pH 8.0 and 40 °C indicates the adoption of a favorable protein conformation with a high number of buried tryptophan residues, reducing solvent exposure. Appearance of an intense Amide I absorption band at pH 8.0 corroborates an intact secondary structure. A lower enthalpy value for pH 4.0 over pH 8.0 and 12.0 in the differential scanning calorimetric data corroborates the stability of the lipase at alkaline conditions, while a low K_m (0.68 ± 0.03 mM) for tributyrin verifies the high affinity of lipase KV1 for the substrate. The data, herein offer useful insights into future structure-based tunable catalytic activity of lipase KV1.

Stable bioemulsifiers are produced by Acinetobacter bouvetii UAM25 growing in different carbon sources

Acinetobacter species are identified as producing surface-active and emulsifying molecules known as bioemulsifiers. Production, characterization and stability of bioemulsifiers produced by Acinetobacter bouvetii UAM25 were studied. A. bouvetii UAM25 grew in three different carbon and energy sources: ethanol, a glycerol-hexadecane mixture and waste cooking oil in an airlift bioreactor, showing that bioemulsifier production was growth associated. The three purified bioemulsifiers were lipo-heteropolysaccharides of high molecular weight (4866 ± 533 and 462 ± 101 kDa). The best carbon source and energy for bioemulsifier production was wasted cooking oil, with a highest emulsifying capacity (76.2 ± 3.5 EU mg^-1) as compared with ethanol (46.6 ± 7.1 EU mg^-1) and the glycerol-hexadecane mixture (49.5 ± 4.2 EU mg^-1). The three bioemulsifiers in our study displayed similar macromolecular structures, regardless of the nature (hydrophobic or hydrophilic) of the carbon and energy source. Bioemulsifiers did not decrease surface tension, but the emulsifying capacity of all of them was retained under extreme variation in salinity (0-50 g NaCl L^-1), pH (3-10) and temperature (25-121 °C), indicative of remarkable stability. These findings contribute to understanding of the relationship between: production, physical properties, chemical composition and stability of bioemulsifiers for their potential applications in biotechnology, such as bioremediation of hydrocarbon-contaminated soil and water.

Immobilization and characterization of a new regioselective and enantioselective lipase obtained from a metagenomic library

In previous work, a new lipase and its cognate foldase were identified and isolated from a metagenomic library constructed from soil samples contaminated with fat. This new lipase, called LipG9, is a true lipase that shows specific activities that are comparable to those of well-known industrially-used lipases with high activity against long-chain triglycerides. In the present work, LipG9 was co-expressed and co-immobilized with its foldase, on an inert hydrophobic support (Accurel MP1000). We studied the performance of this immobilized LipG9 (Im-LipG9) in organic media, in order to evaluate its potential for use in biocatalysis. Im-LipG9 showed good stability, maintaining a residual activity of more than 70% at 50 °C after incubation in n-heptane (log P 4.0) for 8 h. It was also stable in polar organic solvents such as ethanol (log P -0.23) and acetone (log P -0.31), maintaining more than 80% of its original activity after 8 h incubation at 30 °C. The synthesis of ethyl esters was tested with fatty acids of different chain lengths in n-heptane at 30 °C. The best conversions (90% in 3 h) were obtained for medium and long chain saturated fatty acids (C8, C14 and C16), with the maximum specific activity, 29 U per gram of immobilized preparation, being obtained with palmitic acid (C16). Im-LipG9 was sn-1,3-specific. In the transesterification of the alcohol (R,S)-1-phenylethanol with vinyl acetate and the hydrolysis of the analogous ester, (R,S)-1-phenylethyl acetate, Im-LipG9 showed excellent enantioselectivity for the R-isomer of both substrates (E> 200), giving an enantiomeric excess (ee) of higher than 95% for the products at 49% conversion. The results obtained in this work provide the basis for the development of applications of LipG9 in biocatalysis.

First co-expression of a lipase and its specific foldase obtained by metagenomics

Background

Metagenomics is a useful tool in the search for new lipases that might have characteristics that make them suitable for application in biocatalysis. This paper reports the cloning, co-expression, purification and characterization of a new lipase, denominated LipG9, and its specific foldase, LifG9, from a metagenomic library derived from a fat-contaminated soil.

Results

Within the metagenomic library, the gene lipg9 was cloned jointly with the gene of the foldase, lifg9. LipG9 and LifG9 have 96% and 84% identity, respectively, with the corresponding proteins of Aeromonas veronii B565. LipG9 and LifG9 were co-expressed, both in N-truncated form, in Escherichia coli BL21(DE3), using the vectors pET28a(+) and pT7-7, respectively, and then purified by affinity chromatography using a Ni²⁺ column (HiTrap Chelating HP). The purified enzyme eluted from the column complexed with its foldase. The molecular masses of the N-truncated proteins were 32 kDa for LipG9, including the N-terminal His-tag with 6 residues, and 23 kDa for LifG9, which did not have a His-tag. The biochemical and kinetic characteristics of the purified lipase-foldase preparation were investigated. This preparation was active and stable over a wide range of pH values (6.5-9.5) and temperatures (10-40°C), with the highest specific activity, of 1500 U mg⁻¹, being obtained at pH 7.5 at 30°C. It also had high specific activities against tributyrin, tricaprylin and triolein, with values of 1852, 1566 and 817 U mg⁻¹, respectively. A phylogenetic analysis placed LipG9 in the lipase subfamily I.1. A comparison of the sequence of LipG9 with those of other bacterial lipases in the Protein Data Bank showed that LipG9 contains not only the classic catalytic triad (Ser¹⁰³, Asp²⁵⁰, His²⁷²), with the catalytic Ser occurring within a conserved pentapeptide, Gly-His-Ser-His-Gly, but also a conserved disulfide bridge and a conserved calcium binding site. The homology-modeled structure presents a canonical α/β hydrolase folding type I.

Conclusions

This paper is the first to report the successful co-expression of a lipase and its associated foldase from a metagenomic library. The high activity and stability of Lip-LifG9 suggest that it has a good potential for use in biocatalysis.

Electronic supplementary material

The online version of this article (doi:10.1186/s12934-014-0171-7) contains supplementary material, which is available to authorized users.

Probing the molecular determinant of the lipase-specific foldase Lif26 for the interaction with its cognate Lip26

As a steric chaperone, the lipase-specific foldase Lif26 from Acinetobacter sp. XMZ-26 is required for correct folding of the lipase Lip26 in in vivo co-expression and in vitro refolding systems. Lif26 interacts with Lip26 as determined by yeast two hybrid assays in vivo and GST pull-down experiments in vitro. To study the molecular determinants of the interaction between Lif26 and Lip26, a homology model-based screening of residues, molecular dynamics (MD) simulation-based calculation of interaction energies, and site-directed mutagenesis to alter individual screened residues were applied. One conserved amino acid in the C-terminal mini-domain of Lif26, Arg332, was involved in the interaction with Lip26. Arg332 could not be replaced by any other residue, based on saturated site-directed mutagenesis, and it formed a conserved and stable salt bridge with Glu112 of Lip26, which may contribute to binding specificity. The residues surrounding Arg332, such as Trp288 in α9, likely stabilized Arg332 in the proper conformation for the interaction with Lip26.