Stimulation of lipase production during bacterial growth on alkanes

Hydrolysis of Methylumbeliferyl Substrate Proxies for Esterase Activities as Indicator for Microbial Oil Degradation in the Ocean: Evidence from Observations in the Aftermath of the Deepwater Horizon Oil Spill (Gulf of Mexico)

Biological oil weathering facilitated by specialized heterotrophic microbial communities plays a key role in the fate of petroleum hydrocarbon in the ocean. The most common methods of assessing oil biodegradation involve (i) measuring changes in the composition and concentration of oil over time and/or (ii) biological incubations with stable or radio-labelled substrates. Both methods provide robust and invaluable information on hydrocarbon biodegradation pathways; however, they also require extensive sample processing and are expensive in nature. More convenient ways to assess activities within microbial oil degradation networks involve measuring extracellular enzyme activity. This perspective article synthesizes previously published results from studies conducted in the aftermath of the 2010 Deepwater Horizon (DwH) oil spill in the northern Gulf of Mexico (nGoM), to test the hypothesis that fluorescence assays of esterases, including lipase activity, are sensitive indicators for microbial oil degradation in the ocean. In agreement with the rates and patterns of enzyme activity in oil-contaminated seawater and sediments in the nGoM, we found close correlations between esterase activity measured by means of methylumbeliferyl (MUF) oleate and MUF butyrate hydrolysis, and the concentration of petroleum hydrocarbons in two separate laboratory incubations using surface (<1 m) and deep nGoM waters (>1200 m). Correlations between esterase activities and oil were driven by the presence of chemical dispersants, suggesting a connection to the degree of oil dissolution in the medium. Our results clearly show that esterase activities measured with fluorogenic substrate proxies are a good indicator for oil biodegradation in the ocean; however, there are certain factors as discussed in this study that need to be taken into consideration while utilizing this approach.

Looking through the FOG: microbiome characterization and lipolytic bacteria isolation from a fatberg site

Sewer systems are complex physical, chemical and microbial ecosystems where fats, oils and grease (FOG) present a major problem for sewer management. Their accumulation can lead to blockages (‘Fatbergs’), sewer overflows and disruption of downstream wastewater treatment. Further advancements of biological FOG treatments need to be tailored to degrade the FOG, and operate successfully within the sewer environment. In this study we developed a pipeline for isolation of lipolytic strains directly from two FOG blockage sites in the UK, and isolated a range of highly lipolytic bacteria. We selected the five most lipolytic strains using Rhodamine B agar plates and pNP-Fatty acid substrates, with two Serratia spp., two Klebsiella spp. and an environmental Acinetobacter strain that all have the capacity to grow on FOG-based carbon sources. Their genome sequences identified the genetic capacity for fatty acid harvesting (lipases), catabolism and utilization (Fad genes). Furthermore, we performed a preliminary molecular characterization of the microbial community at these sites, showing a diverse community of environmental bacteria at each site, but which did include evidence of sequences related to our isolates. This study provides proof of concept to isolation strategies targeting Fatberg sites to yield candidate strains with bioremediation potential for FOG in the wastewater network. Our work sets the foundation for development of novel bioadditions tailored to the environment with non-pathogenic Acinetobacter identified as a candidate for this purpose.

Unraveling the lipolytic activity of thermophilic bacteria isolated from a volcanic environment

In a bioprospecting effort towards novel thermostable lipases, we assessed the lipolytic profile of 101 bacterial strains isolated from the volcanic area of Santorini, Aegean Sea, Greece. Screening of lipase activity was performed both in agar plates and liquid cultures using olive oil as carbon source. Significant differences were observed between the two screening methods with no clear correlation between them. While the percentage of lipase producing strains identified in agar plates was only 17%, lipolytic activity in liquid culture supernatants was detected for 74% of them. Nine strains exhibiting elevated extracellular lipase activities were selected for lipase production and biochemical characterization. The majority of lipase producers revealed high phylogenetic similarity with Geobacillus species and related genera, whilst one of them was identified as Aneurinibacillus sp. Lipase biosynthesis strongly depended on the carbon source that supplemented the culture medium. Olive oil induced lipase production in all strains, but maximum enzyme yields for some of the strains were also obtained with Tween-80, mineral oil, and glycerol. Partially purified lipases revealed optimal activity at 70–80°C and pH 8-9. Extensive thermal stability studies revealed marked thermostability for the majority of the lipases as well as a two-step thermal deactivation pattern.

Isolation and characterization of a monoaromatic hydrocarbon-degrading bacterium, Pseudomonas aeruginosa from crude oil

The present study reports on the isolation and characterization of a Pseudomonas aeruginosa strain PTz-5 from crude oil from oil field sampled in Assam, India. It was capable to utilize hexadecane, benzene or toluene as a sole source of carbon aerobically. Strain PTz-5 was able to produce extracellular lipase that catalyzed triglycerides to free fatty acid and glycerol. The lipase activity was stable in the temperature range of 40 to 60 degrees C. Strain PTz-5 avidly adhered to the surface of hydrocarbon droplets during their growth in liquid culture medium. These properties could play an essential role in hydrocarbon degradation. The results presented here highlight the metabolic versatility and hydrocarbon biodegradative capability of strain PTz-5, signifying its great potential for the bioremediation of various hydrocarbon-contaminated environments.

Identification and characterization of xcpR encoding a subunit of the general secretory pathway necessary for dodecane degradation in Acinetobacter calcoaceticus ADP1

A mutant of Acinetobacter calcoaceticus ADP1 unable to grow on alkanes was complemented for growth on hexadecane with a DNA fragment encoding a protein with homology to XcpR, a subunit of the general secretion pathway for exoproteins in Pseudomonas aeruginosa. Insertional inactivation of xcpR in A. calcoaceticus ADP1 by transcriptional fusion to lacZ abolishes secretion of lipase and esterase and leads to lack of growth on dodecane and slower growth on hexadecane. We, therefore, propose the participation of a secreted protein in alkane degradation.

Utilization and degradation of an ester-based synthetic lubricant by Acinetobacter lwoffi

An oil-degrading bacterium, Acinetobacter lwoffi, isolated by elective culture from the Medway estuary, utilized an ester-based synthetic lubricating oil EMKARATE DE 155 as sole carbon and energy source. Analysis of culture supernatants by gas chromatography showed the accumulation of a nondegradable metabolite 1,1,1 Tris (hydroxymethyl)propane in addition to two metabolizable fatty acids, octanoic and decanoic acids as products of the synthetic oil degradation. Esterase activities were subsequently demonstrated in oil and acetate-grown cells. The synthetic oil therefore appears to be partially biodegradable in the environment.

Two genes encoding proteins with similarities to rubredoxin and rubredoxin reductase are required for conversion of dodecane to lauric acid in Acinetobacter calcoaceticus ADP1

Mutants of Acinetobacter calcoaceticus ADP1 unable to grow on dodecane, but retaining the ability to grow on lauric acid were isolated after ethylmethanesulphonate (EMS) treatment. This growth deficiency was complemented by a clone from a gene library constructed from chromosomal DNA of the wild-type strain. The complementing DNA mapped in a gene encoding a polypeptide with homology to rubredoxins. The deduced putative rubredoxin amino acid sequence is more similar to related proteins from Gram-positive bacteria than to the Pseudomonas oleovorans rubredoxin involved in alkane oxidation. An adjacent gene encodes a protein with similarity to rubredoxin reductase from Pseudomonas oleovorans and related NAD(P)-dependent reductases. Disruption of the rubredoxin-encoding gene by insertion of a KmR/lacZ cassette rendered the resulting strain unable to grow on dodecane or hexadecane. This demonstrates that these genes are necessary for alkane degradation. Transcriptional fusion of lacZ to the rubredoxin-encoding gene led to low level constitutive beta-galactosidase expression, whereas the fusion oriented in the opposite direction was not expressed.

Characterization of the extracellular lipase, LipA, of Acinetobacter calcoaceticus BD413 and sequence analysis of the cloned structural gene

The extracellular lipase from Acinetobacter calcoaceticus BD413 was purified to homogeneity, via hydrophobic-interaction fast performance liquid chromatography (FPLC), from cultures grown in mineral medium with hexadecane as the sole carbon source. The enzyme has an apparent molecular mass of 32 kDa on SDS-polyacrylamide gels and hydrolyses long acyl chain p-nitrophenol (pNP) esters, like pNP palmitate (pNPP), with optimal activity between pH 7.8 and 8.8. Additionally, the enzyme shows activity towards triglycerides such as olive oil and tributyrin and towards egg-yolk emulsions. The N-terminal amino acid sequence of the mature protein was determined, and via reverse genetics the structural lipase gene was cloned from a gene library of A. calcoaceticus DNA in Escherichia coli phage M13. Sequence analysis of a 2.1 kb chromosomal DNA fragment revealed one complete open reading frame, lipA, encoding a mature protein with a predicted molecular mass of 32.1 kDa. This protein shows high similarity to known lipases, especially Pseudomonas lipases, that are exported in a two-step secretion mechanism and require a lipase-specific chaperone. The identification of an export signal sequence at the N-terminus of the mature lipase suggests that the lipase of Acinetobacter is also exported via a two-step translocation mechanism. However, no chaperone-encoding gene was found downstream of lipA, unlike the situation in Pseudomonas. Analysis of an A. calcoaceticus mutant showing reduced lipase production revealed that a periplasmic disulphide oxidoreductase is involved in processing of the lipase. Via sequence alignments, based upon the crystal structure of the closely related Pseudomonas glumae lipase, a model has been made of the secondary-structure elements in AcLipA. The active site serine of AcLipA was changed to an alanine, via site-directed mutagenesis, resulting in production of an inactive extracellular lipase.

Biodegradation of a synthetic lubricant by Micrococcus roseus

A bacterium that was able to utilize Emkarate 1550 (E1550), a synthetic lubricant ester, as the sole source of carbon was isolated. The isolate was tentatively identified as Micrococcus roseus. The components of the E1550 ester, octanoate, decanoate, and 1,1,1-tris(hydroxymethyl)propane (TMP), were detected in the culture medium of cells growing on the ester. The TMP tertiary alcohol accumulated during growth and was not utilized by this isolate. The detection of the components of the ester in the supernatant of cultures indicated that one of the first steps in its degradation was cleavage of the ester bonds. Esterase activity was significantly enhanced in cells grown on E1550 compared with esterase activity measured in cells grown on acetate.

Production, purification, and properties of a lipase from a bacterium (Pseudomonas aeruginosa YS-7) capable of growing in water-restricted environments

An extracellular lipase from the low-water-tolerant bacterium P. aeruginosa YS-7 was produced, purified, and characterized with respect to its functional properties in aqueous solutions and organic solvents. The enzyme was partially released from the cells during fermentation in defined medium with 5% (wt/vol) soybean oil. Approximately one-half of the total culture activity remained in solution after removal of cells. More than 95% of the activity was found in culture supernatant after mild detergent treatment (10 mM sodium deoxycholate) or after shifting the carbon source during the fermentation from triglyceride to a free fatty acid. The enzyme was recovered from an acetone precipitate of the whole culture and purified by hydrophobic interaction chromatography, yielding a preparation having a specific activity of about 1,300 mumol of fatty acid mg-1 h-1. The lipase (molecular size, approximately 40 kDa) hydrolyzes a variety of fatty acid esters and has an optimum pH of about 7. The enzyme retained its full activity at 20 to 55 degrees C, even after prolonged exposure (more than 30 days) to different concentrations of water-miscible organic solvents such as alcohols, glycols, pyridine, acetonitrile, dimethyl formamide, and dimethyl sulfoxide. The hydrolysis of 4-nitrophenyl laurate ester and of triglyceride emulsified in water was slightly accelerated with increasing concentrations of alcohols and glycols up to about 20% but was abolished with a further increase in alcohol concentration or in the presence of acetonitrile. In contrast, the rate of hydrolysis of these substrates in concentrated solutions of dimethyl formamide or dimethyl sulfoxide was markedly increased, by more than twofold and more than fivefold, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)