Physiological factors affecting production of extracellular lipase (LipA) in Acinetobacter calcoaceticus BD413: fatty acid repression of lipA expression and degradation of LipA

Transcriptional response of short-term nanoplastic exposure in Monodonta labio

Although nanoplastic (NP) pollution across aquatic environments has elicited widespread attention in recent years, its associated risks remain unclear. Using intertidal Monodonta labio as the test organism, RNA-Seq was performed to analyze the expression levels of genes under acute exposure to different concentrations of NPs in this study. A large quantity of differentially expressed genes (DEGs) were detected in response to three concentrations (0.1, 1, and 10 mg/L) of NPs. The expression levels of genes related to immunity, oxidative stress, and apoptosis were altered after NP exposure, and most of them were suppressed. These findings establish the foundation for future research on the biological effects of NP ingestion among aquatic organisms and their potential effects on humans via the consumption of these marine resources. However, further research on DEGs is needed to gain a better understanding of the molecular mechanisms behind their responses to NP toxicity in aquatic organisms.

Transcriptional response provides insights into the effect of chronic polystyrene nanoplastic exposure on Daphnia pulex

Nanoplastic pollution is widespread and persistent across global water systems and can cause a negative effect on aquatic organisms, especially the zooplankter which is the keystone of the food chain. The present study uses RNA sequencing to assess the global change in gene expression caused by 21 days of exposure to 75 nm polystyrene (PS) nanoplastics on Daphnia pulex, a model organism for ecotoxicity. With the threshold value at P value < 0.05 and fold change >2, 244 differentially expressed genes were obtained. Combined with real-time PCR validation of several selected genes, our results indicated that a distinct expression profile of key genes, including downregulated trehalose transporter, trehalose 6-phosphate synthase/phosphatase, chitinase and cathepsin-L as well as upregulated doublesex 1 and doublesex and mab-3 related transcription factor-like protein, contributed to the toxic effects of chronic nanoplastic exposure on Daphnia, such as slowed growth, subdued reproductive ability and reproductive pattern shifting. Our study also showed that chronic exposure to nanoplastic changed the sex ratio of D. pulex neonates. By integrating the gene expression pattern in an important model organism, this study gained insight into the molecular mechanisms of the toxic effect of chronic PS nanoplastic exposure on D. pulex, which may also extend to other nanoplastics or aquatic animals.

Molecular characterization of a proteolysis-resistant lipase from Bacillus pumilus SG2

Proteolysis-resistant lipases can be well exploited by industrial processes which employ both lipase and protease as biocatalysts. A proteolysis resistant lipase from Bacillus pumilus SG2 was isolated, purified and characterized earlier. The lipase was resistant to native and commercial proteases. In the present work, we have characterized the lip gene which encodes the proteolysis-resistant lipase from Bacillus pumilus SG2. The parameters and structural details of lipase were analysed. The lip gene consisted of 650 bp. The experimental molecular weight of SG2 lipase was nearly double that of its theoretical molecular weight, thus suggesting the existence of the functional lipase as a covalent dimer. The proteolytic cleavage sites of the lipase would have been made inaccessible by dimerisation, thus rendering the lipase resistant to protease.

Cloning, sequencing, and characterization of lipase genes from a polyhydroxyalkanoate (PHA)-synthesizing Pseudomonas resinovorans

Lipase (lip) and lipase-specific foldase (lif) genes of a biodegradable polyhydroxyalkanoate (PHA)-synthesizing Pseudomonas resinovorans NRRL B-2649 were cloned using primers based on consensus sequences, followed by polymerase chain reaction-based genome walking. Sequence analyses showed a putative Lip gene product (314 amino acids, a.a.) with its catalytic active site (Ser(111), Asp(258), and His(280)) identified. The foldase lif gene that is located 55 bp downstream of lip codes for a putative Lif (345 a.a.). To verify the biological function of the cloned lip gene for lipase expression in P. resinovorans, we constructed a lip knock-out mutant (lip::Tn5<KAN-2>) by transposon insertion. Complementation of the lip knock-out P. resinovorans mutant with a lipase expression plasmid (pBS29-P2-lip) was performed, and its effect on lipase expression was investigated. The wild-type P. resinovorans and the lip::Tn5<KAN-2>[pBS29-P2-lip] recombinant (but not the lip::Tn5<KAN-2> mutant) showed fluorescence on rhodamine B plates indicative of lipase activity. The wild type exhibited extracellular lipase activity when grown on medium containing triacylglycerol substrates (tallow, olive oil, and tributyrin) as sole carbon sources, but the lip::Tn5<KAN-2> mutant did not show such activity. Lipase activity of various strains was also confirmed by TLC analysis of the composition of acylglycerols and free fatty acid in the extracts of the spent culture medium. We further found that tributyrin was more effective than olive oil in inducing lipase expression in P. resinovorans.

Concomitant production of protease and lipase by Bacillus Licheniformis VSG1: Production, purification and characterization

This study was aimed at producing protease and lipase simultaneously on a common medium by Bacillus licheniformis VSG1, which was isolated from a tannery effluent. The effect of media composition with respect to protein source, lipid source and emulsifier on the production of protease and lipase was analysed. Both those enzymes were produced under optimized conditions like pH, temperature and incubation time. The enzyme mixture comprising of both protease and lipase was purified by ammonium sulphate precipitation, dialysis and gel filtration chromatography to obtain 20-fold pure enzymes. The purified enzyme mixture was characterized to determine the optimum pH and temperature of protease and lipase, the response of the enzymes to inhibitors, additives and solvents. The molecular weight of both the enzymes was determined as 40 kDa on SDS-PAGE. The concomitant production of protease and lipase and the purification of both the enzymes in a single mixture have industrial significance, as many industrial processes use both protease and lipase together.

Hexadecane and Tween 80 stimulate lipase production in Burkholderia glumae by different mechanisms

Burkholderia glumae strain PG1 produces a lipase of biotechnological relevance. Lipase production by this strain and its derivative LU8093, which was obtained through classical strain improvement, was investigated under different conditions. When 10% hexadecane was included in the growth medium, lipolytic activity in both strains could be increased approximately 7-fold after 24 h of growth. Hexadecane also stimulated lipase production in a strain containing the lipase gene fused to the tac promoter, indicating that hexadecane did not affect lipase gene expression at the transcriptional level, which was confirmed using lipA-gfp reporter constructs. Instead, hexadecane appeared to enhance lipase secretion, since the amounts of lipase in the culture supernatant increased in the presence of hexadecane, with a concomitant decrease in the cells, even when protein synthesis was inhibited with chloramphenicol. In the presence of olive oil as a carbon source, nonionic detergents, such as Tween 80, increased extracellular lipase activity twofold. Like hexadecane, Tween 80 appeared to stimulate lipase secretion, although in a more disruptive manner, since other, normally nonsecreted proteins were found in the culture supernatant. Additionally, like olive oil, Tween 80 was found to induce lipase gene expression in strain PG1 in medium containing sucrose as a carbon source but not in glucose-containing medium, suggesting that lipase gene expression is prone to catabolite repression. In contrast, lipase production in the lipase-overproducing strain LU8093 was independent of the presence of an inducer and was not inhibited by glucose. In conclusion, hexadecane and Tween 80 enhance lipase production in B. glumae, and they act via different mechanisms.

OPPORTUNITIES FOR GENETIC INVESTIGATION AFFORDED BYACINETOBACTER BAYLYI, A NUTRITIONALLY VERSATILE BACTERIAL SPECIES THAT IS HIGHLY COMPETENT FOR NATURAL TRANSFORMATION

The genetic and physiological properties of Acinetobacter baylyi strain ADP1 make it an inviting subject for investigation of the properties underlying its nutritional versatility. The organism possesses a relatively small genome in which genes for most catabolic functions are clustered in several genetic islands that, unlike pathogenicity islands, give little evidence of horizontal transfer. Coupling mutagenic polymerase chain reaction to natural transformation provides insight into how structure influences function in transporters, transcriptional regulators, and enzymes. With appropriate selection, mutants in which such molecules have acquired novel function may be obtained. The extraordinary competence of A. baylyi for natural transformation and the ease with which it expresses heterologous genes make it a promising platform for construction of novel metabolic systems. Steps toward this goal should take into account the complexity of existing pathways in which transmembrane trafficking plays a significant role.

Sequential parametric optimization of lipase production by a mutant strain Rhizopus sp. BTNT-2

Lipase production by the mutant strain Rhizopus sp. BTNT-2 was optimized in submerged fermentation. Different chemical and physical parameters such as carbon sources, nitrogen sources, oils, inoculum level, pH, incubation time, incubation temperature and aeration have been extensively studied to increase lipase productivity. Potato starch (1.25% w/v) as a carbon source, corn steep liquor (1.5% w/v) as a nitrogen source and olive oil (0.5% v/v) as lipid source were found to be optimal for lipase production. The optimal levels of other parameters are 4 ml of inoculum (2.6x10(8) spores/ml), initial pH of 5.5, incubation time of 48 hours, incubation temperature of 28 degrees C and aeration rate of 120 rpm. With the optimized parameters, the highest production of lipase was 59.2 U/ml while an yield of only 28.7 U/ml was obtained before optimization resulting in 206% increase in the productivity.

Isolation and characterization of Acinetobacter sp. ES-1 excreting a lipase with high enantioselectivity for (S)-ketoprofen ethyl ester

A new Acinetobacter sp. ES-1, grown on triolein, tryptone and Triton X-100, excreted a lipase that hydrolyzed 10 mM (R,S)-ketoprofen ethyl ester into (S)-ketoprofen. The crude lipase had an activity of 10 U ml(-1) and, at 30 degrees C and pH 7 over 48 h, gave a conversion yield of 35% with an enantiomeric excess for the product 96%.

Acinetobacter lipases: molecular biology, biochemical properties and biotechnological potential

Lipases (EC 3.1.1.3) have received increased attention recently, evidenced by the increasing amount of information about lipases in the current literature. The renewed interest in this enzyme class is due primarily to investigations of their role in pathogenesis and their increasing use in biotechnological applications. Also, many microbial lipases are available as commercial products, the majority of which are used in detergents, cosmetic production, food flavoring, and organic synthesis. Lipases are valued biocatalysts because they act under mild conditions, are highly stable in organic solvents, show broad substrate specificity, and usually show high regio- and/or stereo-selectivity in catalysis. A number of lipolytic strains of Acinetobacter have been isolated from a variety of sources and their lipases possess many biochemical properties similar to those that have been developed for biotechnological applications. This review discusses the biology of lipase expression in Acinetobacter, with emphasis on those aspects relevant to potential biotechnology applications.

The improvement of lipase secretion and stability by addition of inert compounds into Acinetobacter calcoaceticus cultures

Acinetobacter calcoaceticus BD413 produces variable amounts of an exocellular lipase that becomes rapidly inactivated upon secretion. To achieve high yield and protect the enzyme, we assayed the addition of several inert compounds to cell-free supernatants, cell fractions, and whole cultures. Glass beads, poly(ethylene glycol) 600, Triton X-100, saccharose, gum arabic, and beta-cyclodextrin were among the compounds tested. beta-Cyclodextrin and gum arabic (and saccharose to a lesser extent) were effective enzyme stabilizers in cell-free supernatants, while gum arabic, glass beads, and Triton X-100 improved lipase secretion from cells, and, therefore, total lipase yield (30-50%, according to the additive). In whole cultures, beta-cyclodextrin was the most effective additive, particularly in combination with glass beads or gum arabic. Indeed, cultures containing beta-cyclodextrin plus gum arabic were able to maintain 95% (+/- 1.5%) of the initial lipase activity for more than 16 h, while control cultures with no additives maintained only 10% (+/- 4%) of the enzyme activity after the same period. In conclusion, the addition of inert compounds in cultures may be considered a useful approach for achieving increased yield and lipase stabilization, amenable for downstream processing.

Purification and properties of the extracellular lipase, LipA, of Acinetobacter sp. RAG-1

An extracellular lipase, LipA, extracted from Acinetobacter sp. RAG-1 grown on hexadecane was purified and properties of the enzyme investigated. The enzyme is released into the growth medium during the transition to stationary phase. The lipase was harvested from cells grown to stationary phase, and purified with 22% yield and > 10-fold purification. The protein demonstrates little affinity for anion exchange resins, with contaminating proteins removed by passing crude supernatants over a Mono Q column. The lipase was bound to a butyl Sepharose column and eluted in a Triton X-100 gradient. The molecular mass (33 kDa) was determined employing SDS/PAGE. LipA was found to be stable at pH 5.8-9.0, with optimal activity at 9.0. The lipase remained active at temperatures up to 70 degrees C, with maximal activity observed at 55 degrees C. LipA is active against a wide range of fatty acid esters of p-nitrophenyl, but preferentially attacks medium length acyl chains (C6, C8). The enzyme demonstrates hydrolytic activity in emulsions of both medium and long chain triglycerides, as demonstrated by zymogram analysis. RAG-1 lipase is stabilized by Ca2+, with no loss in activity observed in preparations containing the cation, compared to a 70% loss over 30 h without Ca2+. The lipase is strongly inhibited by EDTA, Hg2+, and Cu2+, but shows no loss in activity after incubation with other metals or inhibitors examined in this study. The protein retains more than 75% of its initial activity after exposure to organic solvents, but is rapidly deactivated by pyridine. RAG-1 lipase offers potential for use as a biocatalyst.

Characterization of a highly thermostable extracellular lipase from Lactobacillus plantarum

After screening for the presence of lipase activity in lactobacilli isolated from "chouriço", a traditional Portuguese dry fermented sausage, a strain of Lactobacillus plantarum (DSMZ 12028) was chosen for extracellular lipase characterisation and purification. Proteinase K did not significantly affect lipolytic activity, as opposed to trypsin, which completely eliminated this activity. Among NaCl, Ca2+, EDTA, BSA, glycerol, Mn2+ and Mg2+, only Mn2+ and Mg2+ stimulated the lipase. Purification by gel filtration chromatography and gel electrophoresis revealed four bands, between 98 and 45 kDa, all with lipolytic activity against olive oil.

Influence of iron on growth, production of siderophore compounds, membrane proteins, and lipase activity in Acinetobacter calcoaceticus BD 413

Acinetobacter calcoaceticus BD413 was examined for production of siderophores and iron-repressible outer membrane proteins following growth in iron-restricted media. The iron-scavenging phenotype was associated with the secretion of iron-repressible catechol and the induction of a group of six outer membrane proteins with molecular weights ranging from 34 to 85 kDa. The amount of catechol produced was dependent on medium composition and iron stringency. The relation between iron limitation and lipase production was studied at the level of lipA transcription and extracellular lipase activity. In minimal medium, iron limitation slightly affected lipA expression but decreased exo-lipase activity significantly. However, if iron limitation and rich nitrogen sources were simultaneously present in the culture media, the production of lipase was increased approximately 4 times.

Effects of low temperature, cold shock, and various carbon sources on esterase and lipase activities and exopolysaccharide production by a psychrotrophicAcinetobactersp

The activities of isocitrate lyase, esterase, and lipase by the psychrotrophic Acinetobacter sp. strain HH1-1 were monitored during incubation at 25°C, 5°C, and after a 25°C to 5°C down shift in growth temperature. During growth at 25°C, isocitrate lyase activity was detected in cell-free extracts, but at 5°C and after cold shock, activity was measured primarily in the cell culture supernatant. Strain HH1-1 produced two cell-associated esterases and an extracellular esterase and lipase. Activities of the extracellular esterase and lipase were reduced when cells were grown at 5°C and after cold shock. In contrast, an increased synthesis of a 53-kDa cell-associated esterase was observed 50 h after cold shock. An extracellular polysaccharide was also produced, indicated by a decrease in surface tension in cell culture supernatant when cells were incubated at 25°C; but like extracellular enzyme activity, production of the exopolymer was reduced when cells were subjected to low temperatures. These results indicated that the intracellular enzyme, isocitrate lyase, leaked out of the cell after cold shock and during growth at 5°C. The increased activity of a cell-associated esterase suggested this enzyme is required for growth at low temperatures. In contrast, activities of extracellular lipolytic enzymes and production of an extracellular polysaccharide were negatively affected at the lower temperatures.Key words: Acinetobacter, cold shock, esterase, lipase, exopolysaccharide.

Bacterial biocatalysts: molecular biology, three-dimensional structures, and biotechnological applications of lipases

Bacteria produce and secrete lipases, which can catalyze both the hydrolysis and the synthesis of long-chain acylglycerols. These reactions usually proceed with high regioselectivity and enantioselectivity, and, therefore, lipases have become very important stereoselective biocatalysts used in organic chemistry. High-level production of these biocatalysts requires the understanding of the mechanisms underlying gene expression, folding, and secretion. Transcription of lipase genes may be regulated by quorum sensing and two-component systems; secretion can proceed either via the Sec-dependent general secretory pathway or via ABC transporters. In addition, some lipases need folding catalysts such as the lipase-specific foldases and disulfide-bond-forming proteins to achieve a secretion-competent conformation. Three-dimensional structures of bacterial lipases were solved to understand the catalytic mechanism of lipase reactions. Structural characteristics include an alpha/beta hydrolase fold, a catalytic triad consisting of a nucleophilic serine located in a highly conserved Gly-X-Ser-X-Gly pentapeptide, and an aspartate or glutamate residue that is hydrogen bonded to a histidine. Four substrate binding pockets were identified for triglycerides: an oxyanion hole and three pockets accommodating the fatty acids bound at position sn-1, sn-2, and sn-3. The differences in size and the hydrophilicity/hydrophobicity of these pockets determine the enantiopreference of a lipase. The understanding of structure-function relationships will enable researchers to tailor new lipases for biotechnological applications. At the same time, directed evolution in combination with appropriate screening systems will be used extensively as a novel approach to develop lipases with high stability and enantioselectivity.

Phenotypic expression of PCR-generated random mutations in a Pseudomonas putida gene after its introduction into an Acinetobacter chromosome by natural transformation

Localized sets of random point mutations generated by PCR amplification can be transferred efficiently to the chromosome of Acinetobacter ADP1 (also known as strain BD413) by natural transformation. The technique does not require cloning of PCR fragments in plasmids: PCR-amplified DNA fragments are internalized by cells and directly incorporated into their genomes by homologous recombination. Previously such procedures for random mutagenesis could be applied only to Acinetobacter genes affording the selection of mutant phenotypes. Here we describe the construction of a vector and recipient that allow for mutagenesis, recovery, and expression of heterologous genes that may lack a positive selection. The plasmid carries an Acinetobacter chromosomal segment interrupted by a multiple cloning site next to a kanamycin resistance marker. The insertion of heterologous DNA into the multiple cloning site prepares the insert as a target for PCR mutagenesis. PCR amplifies the kanamycin resistance marker and a flanking region of Acinetobacter DNA along with the insert of heterologous DNA. Nucleotide sequence identity between the flanking regions and corresponding chromosomal segments in an engineered Acinetobacter recipient allows homologous recombination of the PCR-amplified DNA fragments into a specific chromosomal docking site from which they can be expressed. The recipient strain contains only a portion of the kanamycin resistance gene, so donor DNA containing both this gene and the mutagenized insert can be selected by demanding growth of recombinants in the presence of kanamycin. The effectiveness of the technique was demonstrated with the relatively GC-rich Pseudomonas putida xylE gene. After only one round of PCR amplification (35 cycles), donor DNA produced transformants of which up to 30% carried a defective xylE gene after growth at 37 degrees C. Of recombinant clones that failed to express xylE at 37 degrees C, about 10% expressed the gene when grown at 22 degrees C. The techniques described here could be adapted to prepare colonies with an altered function in any gene for which either a selection or a suitable phenotypic screen exists.

Effect of oxygen transfer on lipase production by Acinetobacter radioresistens

The influence of oxygen on alkaline lipase production by Acinetobacter radioresistens was studied under two operating modes: controlled dissolved oxygen (DO) concentration and controlled aeration rate. Compared with cell growth, the lipase production depended more extensively on oxygen. The intrinsic factor determining cell growth and lipase production was oxygen transfer rate (OTR) rather than DO concentration. Improvements in OTR, either by aeration or agitation, resulted in an increase in lipase yield and/or a reduction in fermentation time. The formation of A. radioresistens lipase could be described by a mixed-growth-associated model, and the enzyme was mainly a growth-associated product. The overall productivity for the lipase, which depended more strongly on agitation than aeration, could be related with kLa. DO concentration could not be employed in this correlation, though it has been useful as a criterion for ensuring no oxygen limitation in an aerobic fermentation.

bldA-dependent expression of the Streptomyces exfoliatus M11 lipase gene (lipA) is mediated by the product of a contiguous gene, lipR, encoding a putative transcriptional activator

Extracellular lipase synthesis by Streptomyces lividans 66 carrying the cloned lipase gene (lipA) from Streptomyces exfoliatus M11 was found to be growth phase dependent, since lipase was secreted into the medium mainly during the stationary phase; S1 nuclease protection experiments revealed abundant lipA transcripts in RNA preparations obtained during the stationary phase but not in those obtained during exponential growth. Transcription from the lipA promoter was dependent on the presence of lipR, a contiguous downstream gene with a very high guanine-plus-cytosine content (80.2%). The deduced lipR product consists of a protein of 934 amino acids that shows similarity to known transcriptional activators and has a strong helix-turn-helix motif at its C terminus; this motif is part of a domain homologous to DNA-binding domains of bacterial regulators of the UhpA/LuxR superfamily. The lipR sequence revealed the presence of a leucine residue, encoded by the rare TTA codon, which caused bldA dependence of lipA transcription in Streptomyces coelicolor A3(2); replacement of the TTA codon by the alternate CTC leucine codon alleviated bidA dependence but not the apparent growth phase-dependent regulation of lipA transcription. When lipR expression was induced in a controlled fashion during the exponential growth phase, by placing it under the inducible tipA promoter, lipase synthesis was shifted to the exponential growth phase, indicating that the timing of lipR expression, and not its bldA dependence, is the main cause for stationary-phase transcription of lipA.