Cold-active acid β-galactosidase activity of isolated psychrophilic-basidiomycetous yeast Guehomyces pullulans

A new β-galactosidase from Paenibacillus wynnii with potential for industrial applications

Commercial β-galactosidases exhibit undesirable kinetic properties regarding substrate affinity (Michaelis-Menten constant [KM] for lactose) and product inhibition (inhibitor constant [Ki] for galactose). An in silico screening of gene sequences was done and identified a putative β-galactosidase (Paenibacillus wynnii β-galactosidase, BgaPw) from the psychrophilic bacterium Paenibacillus wynnii. The cultivation of the wild-type P. wynnii strain resulted in very low β-galactosidase activities of a maximum of 150 nkat per liter of medium with o-nitrophenyl-β-d-galactopyranoside (oNPGal) as substrate. The recombinant production of BgaPw in Escherichia coli BL21(DE3) increased the yield ∼9,000-fold. Here, a volumetric activity of 1,350.18 ± 11.82 μkatoNPGal/Lculture was achieved in a bioreactor cultivation. The partly purified BgaPw showed a pH optimum at 7.0, a temperature maximum at 40°C, and an excellent stability at 8°C with a half-life of 77 d. Kinetic studies with BgaPw were done in milk or in milk-imitating synthetic buffer (Novo buffer), respectively. Remarkably, the KM value of BgaPw with lactose was as low as 0.63 ± 0.045 mM in milk. It was found that the resulting products of lactose hydrolysis, namely galactose and glucose, did not inhibit the β-galactosidase activity of BgaPw, but instead showed a striking activating effect in both cases (up to 144%). In a comparison study in milk, lactose was completely hydrolyzed by BgaPw in 72 h at 8°C, whereas 2 other known β-galactosidases were less powerful and converted only about 90% of lactose in the same time. Finally, the formation of galactooligosaccharides (GOS) was demonstrated with the new BgaPw, starting with pharma-lactose (400 g/L). A GOS production of about 144 g/L was achieved after 24 h (36.0% yield).

Genomic and proteomic analysis of Tausonia pullulans reveals a key role for a GH15 glucoamylase in starch hydrolysis

Basidiomycetous yeasts remain an almost unexplored source of enzymes with great potential in several industries. Tausonia pullulans (Tremellomycetes) is a psychrotolerant yeast with several extracellular enzymatic activities reported, although the responsible genes are not known. We performed the genomic sequencing, assembly and annotation of T. pullulans strain CRUB 1754 (Perito Moreno glacier, Argentina), a gene survey of carbohydrate-active enzymes (CAZymes), and analyzed its secretome by liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) after growth in glucose (GLU) or starch (STA) as main carbon sources. T. pullulans has 7210 predicted genes, 3.6% being CAZymes. When compared to other Tremellomycetes, it contains a high number of CAZy domains, and in particular higher quantities of glucoamylases (GH15), pectinolytic enzymes (GH28) and lignocellulose decay enzymes (GH7). When the secretome of T. pullulans was analyzed experimentally after growth in starch or glucose, 98 proteins were identified. The 60% of total spectral counts belonged to GHs, oxidoreductases and to other CAZymes. A 65 kDa glucoamylase of family GH15 (TpGA1) showed the highest fold change (tenfold increase in starch). This enzyme contains a conserved active site and showed extensive N-glycosylation. This study increases the knowledge on the extracellular hydrolytic enzymes of basidiomycetous yeasts and, in particular, establishes T. pullulans as a potential source of carbohydrate-active enzymes. KEY POINTS: • Tausonia pullulans genome harbors a high number of genes coding for CAZymes. • Among CAZy domains/families, the glycoside hydrolases are the most abundant. • Secretome analysis in glucose or starch as main C sources identified 98 proteins. • A 65 kDa GH15 glucoamylase showed the highest fold increase upon culture in starch.

Skin Mycobiota of the Captive Giant Panda (Ailuropoda melanoleuca) and the Distribution of Opportunistic Dermatomycosis-Associated Fungi in Different Seasons

Dermatomycosis is the second major cause of morbidity in giant pandas (Ailuropoda melanoleuca), and seriously endangers its health. Previous observations indicated that the occurrence of dermatomycosis in the giant panda varies in different seasons. The skin microbiota is a complex ecosystem, but knowledge on the community structure and the pathogenic potentials of fungi on the skin of the giant panda remains limited. In this study, samples from the giant panda skin in different seasons were collected, and the mycobiota were profiled by 18S rRNA gene sequencing. In total, 375 genera in 38 phyla were detected, with Ascomycota, Basidiomycota, Streptophyta, and Chlorophyta as the predominant phyla and Trichosporon, Guehomyces, Davidiella, Chlorella, Asterotremella, and Klebsormidium as the predominant genera. The skin mycobiota of the giant panda changed in the seasons, and the diversity and abundance of the skin fungi were significantly higher in spring, autumn, and summer than in the winter. Several dermatomycosis-associated fungi were detected as opportunists in the skin mycobiota of healthy giant pandas. Clinical dermatomycosis in the giant panda is observed more in summer and autumn. In this study, the results indicated that the high diversity and abundance of the skin fungi may have enhanced the occurrence of dermatomycosis in autumn and summer, and that dermatomycosis-associated fungi are the normal components of the skin mycobiota.

Overview of lignocellulolytic enzyme systems with special reference to valorization of lignocellulosic biomass

Lignocellulosic biomass, one of the most valuable natural resources, is abundantly present on earth. Being a renewable feedstock, it harbors a great potential to be exploited as a raw material, to produce various value-added products. Lignocellulolytic microorganisms hold a unique position regarding the valorization of lignocellulosic biomass as they contain efficient enzyme systems capable of degrading this biomass. The ubiquitous nature of these microorganisms and their survival under extreme conditions have enabled their use as an effective producer of lignocellulolytic enzymes with improved biochemical features crucial to industrial bioconversion processes. These enzymes can prove to be an exquisite tool when it comes to the eco-friendly manufacturing of value-added products using waste material. This review focuses on highlighting the significance of lignocellulosic biomass, microbial sources of lignocellulolytic enzymes and their use in the formation of useful products.

In Vitro Properties of Potential Probiotic Indigenous Yeasts Originating from Fermented Food and Beverages in Taiwan

Probiotics are live microorganisms that may be able to help prevent and treat some illnesses. Most probiotics on the market are bacterial, primarily Lactobacillus. Yeast are an inevitable part of the microbiota of various fermented foods and beverages and have several beneficial properties that bacteria do not have. In this study, yeast strains were isolated from fermented food and beverages. Various physiological features of the candidate probiotic isolates were preliminarily investigated, including bile salt and acid tolerance, cell surface hydrophobicity, autoaggregation, antioxidant activity, and β-galactosidase activity. Several yeast strains with probiotic potential were selected. Overall, Kluyveromyces marxianus JYC2614 adapted well to the bile salt and acid tolerance test; it also had favorable autoaggregation and good cell-surface hydrophobicity. Klu. marxianus JYC2610 grew well according to the bile salt and acid tolerance test and performed well regarding cell surface hydrophobicity and β-galactosidase activity. Selected yeast species can survive in a gastrointestinal environment and should be further evaluated in vivo as probiotics in the future. Our findings should encourage further studies on the application of the strains in this study as food and feed supplements.

Purified lactases versus whole-cell lactases-the winner takes it all

Lactose-free dairy products are in great demand worldwide due to the high prevalence of lactose intolerance. To make lactose-free dairy products, commercially available β-galactosidase enzymes, also termed lactases, are used to break down lactose to its constituent monosaccharides, glucose and galactose. In this mini-review, the characteristics of lactase enzymes, their origin, and ways of use are discussed in light of their potential for hydrolyzing lactose. We also discuss whole-cell lactase catalysts, which appear to have great potential in terms of cost reduction and convenience, and which are more natural alternatives to purified enzymes. Lactic acid bacteria (LAB) already used in food fermentations seem to be optimal candidates for whole-cell lactases. However, they have not been industrially exploited yet due to technical hurdles. For whole-cell lactases to be efficient, the lactase enzymes inside the cells must be made available for lactose hydrolysis, and thus, cells need to be permeabilized or disrupted prior to use. Here we review state-of-the-art approaches for disrupting or permeabilizing microorganisms. Lastly, based on recent scientific achievements, we propose a novel, resource-efficient, and low-cost scenario for achieving lactose hydrolysis at a dairy plant using a LAB whole-cell lactase.Key points• Lactases (β-galactosidase) are essential for producing lactose-free dairy products• Novel permeabilization techniques facilitate the use of LAB lactases• Whole-cell lactase catalysts have great potential for reducing costs and resources Graphical abstract.

Fungi show broader environmental thresholds in wet than dry agricultural soils with distinct biogeographic patterns

It is critical to establish response thresholds for fungal communities to global environmental change and assess the relationship between fungal diversity and nutrient cycling in soils. However, these have not yet been evaluated in agro-ecosystems. Here we report the findings of a survey across eastern China on the soil fungi and physicochemical properties in adjacent maize and rice fields. The results revealed a wider range of environmental thresholds for soil fungi in rice than maize fields. We found that the dominant fungal taxa only accounted for 0.6% of all taxa, but constituted >50% of total fungi. Based on their habitat preferences, distinct distribution maps between maize and rice fields were constructed, which indicated niche differentiation of soil fungi between dry and waterlogged soils. Rice fields showed higher fungal richness in low latitude regions, consistent with latitudinal richness patterns found in natural terrestrial ecosystems; however, no such trend was observed in maize fields. Fungal richness was positively correlated with nutrient cycling in rice soils and fungal beta diversity with nutrient cycling in maize soils. These findings provide response thresholds for fungal community change across environmental gradients, advancing our understanding of soil fungal diversity patterns in agricultural ecosystems. Differences between wetland and dryland should be taken into consideration when formulating sustainable management plans and baselines for assessments of future global change and resilience of agricultural fields.

Impact of fermentation conditions on the diversity of white colony-forming yeast and analysis of metabolite changes by white colony-forming yeast in kimchi

The presence of white colony-forming yeast (WCFY) on kimchi surfaces indicates a reduction in kimchi quality. This study aimed to investigate the effect of different fermentation temperatures (4, 10, and 20 °C) and packaging conditions (open or closed) on WCFY diversity, and the changes of metabolite by the difference of WCFY diversity. Community analysis using high-throughput DNA sequencing revealed that Kazachstania servazzii and K. barnettii were most prevalent in kimchi fermented under closed packaging condition at 4, 10, and 20 °C. In open packaging condition, four species of Candida sake, K. servazzii, K. barnettii, and Tausonia pullulans were the predominant yeast species at 4 °C, and four species of C. sake, K. servazzii, K. barnettii, and Debaryomyces hancenii were predominantly detected at 10 °C. The diversity of the WCFY community was higher under the open rather than the closed packaging condition. However, at all fermentation temperatures, non-volatile metabolite production by the different WCFY communities did not significantly differ between open and closed packaging conditions, whereas glycerol levels in kimchi samples harboring WCFY increased relative to the control (0 day). These results indicate that fermentation temperature and air exposure can alter WCFY diversity on kimchi surface, however, non-volatile metabolite profiles in kimchi soup are not significantly affected by the difference of WCFY diversity caused by packaging conditions. This study furthers the current understanding of the growth of undesirable WCFY in kimchi.

Assessment of the microbial diversity of Chinese Tianshan tibicos by single molecule, real-time sequencing technology

Chinese Tianshan tibico grains were collected from the rural area of Tianshan in Xinjiang province, China. Typical tibico grains are known to consist of polysaccharide matrix that embeds a variety of bacteria and yeasts. These grains are widely used in some rural regions to produce a beneficial sugary beverage that is slightly acidic and contains low level of alcohol. This work aimed to characterize the microbiota composition of Chinese Tianshan tibicos using the single molecule, real-time sequencing technology, which is advantageous in generating long reads. Our results revealed that the microbiota mainly comprised of the bacterial species of Lactobacillus hilgardii, Lactococcus raffinolactis, Leuconostoc mesenteroides, Zymomonas mobilis, together with a Guehomyces pullulans-dominating fungal community. The data generated in this work helps identify beneficial microbes in Chinese Tianshan tibico grains.

Cloning, Expression and Characterization of a Novel Cold-adapted β-galactosidase from the Deep-sea Bacterium Alteromonas sp. ML52

The bacterium Alteromonas sp. ML52, isolated from deep-sea water, was found to synthesize an intracellular cold-adapted β-galactosidase. A novel β-galactosidase gene from strain ML52, encoding 1058 amino acids residues, was cloned and expressed in Escherichia coli. The enzyme belongs to glycoside hydrolase family 2 and is active as a homotetrameric protein. The recombinant enzyme had maximum activity at 35 °C and pH 8 with a low thermal stability over 30 °C. The enzyme also exhibited a K_m of 0.14 mM, a V_max of 464.7 U/mg and a k_cat of 3688.1 S^-1 at 35 °C with 2-nitrophenyl-β-d-galactopyranoside as a substrate. Hydrolysis of lactose assay, performed using milk, indicated that over 90% lactose in milk was hydrolyzed after incubation for 5 h at 25 °C or 24 h at 4 °C and 10 °C, respectively. These properties suggest that recombinant Alteromonas sp. ML52 β-galactosidase is a potential biocatalyst for the lactose-reduced dairy industry.

Potential characterization of yeasts isolated from Kazak artisanal cheese to produce flavoring compounds

Cheese is a typical handcrafted fermented food in Kazak minority from the Uighur Autonomy Region in China and Central Asia. Among the microbial community that is responsible for Kazak cheese fermentation, yeasts play important role in flavor formation during ripening. To develop ripening cultures, we isolated 123 yeasts from 25 cheese products in Kazak, and identified 87 isolates by the D1/D2 domain of the large subunit rRNA gene sequence. Pichia kudriavzevii was the dominant yeast in Kazak cheese, followed by Kluyveromyces marxianus and Kluyveromyces lactis. Of these, the ability to exhibit enzyme of dominant isolates and contribution to the typical flavor of cheeses was assessed. Enzyme producing yeast strains were inoculated in Hazak cheese‐like medium and volatile compounds were identified by head space solid phase micro extraction coupled to gas chromatography and mass spectroscopy. Pichia kudriavzevii N‐X displayed the strongest extracellular proteolytic and activity on skim milk agar and produced a range of aroma compounds (ethanol, ethyl acetate, 3‐methylbutanol, and acetic acid) for Kazak cheese flavor, could be explored as ripening cultures in commercial production of Kazak cheeses.

Beta galactosidases in Arabidopsis and tomato - a mini review

Beta galactosidases (BGALs) are glycosyl hydrolases that remove terminal β-D-galactosyl residues from β-D-galactosides. There are 17 predicted BGAL genes in the genomes of both Arabidopsis (BGAL1-17) and tomato (TBG1-17). All tested BGALs have BGAL activity but their distinct expression profiles and ancient phylogenetic separation indicates that these enzymes fulfil diverse, non-redundant roles in plant biology. The majority of these BGALs are predicted to have signal peptide and thought to act during cell wall-related biological processes. Interestingly, deletion of BGAL6 and BGAL10 in Arabidopsis causes reduced mucilage release during seed imbibition and shorter siliques respectively, whereas TBG4 depletion by RNAi decreases in fruit softening in tomato. The majority of plant BGALs remain to be characterized.

Yeasts from sub-Antarctic region: biodiversity, enzymatic activities and their potential as oleaginous microorganisms

Various microbial groups are well known to produce a range of extracellular enzymes and other secondary metabolites. However, the occurrence and importance of investment in such activities have received relatively limited attention in studies of Antarctic soil microbiota. Sixty-one yeasts strains were isolated from King George Island, Antarctica which were characterized physiologically and identified at the molecular level using the D1/D2 region of rDNA. Fifty-eight yeasts (belonging to the genera Cryptococcus, Leucosporidiella, Rhodotorula, Guehomyces, Candida, Metschnikowia and Debaryomyces) were screened for extracellular amylolytic, proteolytic, esterasic, pectinolytic, inulolytic xylanolytic and cellulolytic activities at low and moderate temperatures. Esterase activity was the most common enzymatic activity expressed by the yeast isolates regardless the assay temperature and inulinase was the second most common enzymatic activity. No cellulolytic activity was detected. One yeast identified as Guehomyces pullulans (8E) showed significant activity across six of seven enzymes types tested. Twenty-eight yeast isolates were classified as oleaginous, being the isolate 8E the strain that accumulated the highest levels of saponifiable lipids (42 %).

Screening and Characterization of Cold-Active β-Galactosidase Producing Psychrotrophic Enterobacter ludwigii from the Sediments of Arctic Fjord

Low-temperature-tolerant microorganisms and their cold-active enzymes could be an innovative and invaluable tool in various industrial applications. In the present study, bacterial isolates from the sediment samples of Kongsfjord, Norwegian Arctic, were screened for β-galactosidase production. Among the isolates, KS25, KS85, KS60, and KS92 have shown good potential in β-galactosidase production at 20 °C. 16SrRNA gene sequence analysis revealed the relatedness of the isolates to Enterobacter ludwigii. The optimum growth temperature of the isolate was 25 °C. The isolate exhibited good growth and enzyme production at a temperature range of 15-35 °C, pH 5-10. The isolate preferred yeast extract and lactose for the maximum growth and enzyme production at conditions of pH 7.0, temperature of 25 °C, and agitation speed of 100 rpm. The growth and enzyme production was stimulated by Mn²⁺ and Mg²⁺ and strongly inhibited by Zn²⁺, Ni²⁺, and Cu⁺. β-Galactosidases with high specific activity at low temperatures are very beneficial in food industry to compensate the nutritional problem associated with lactose intolerance. The isolate exhibited a remarkable capability to utilize clarified whey, an industrial pollutant, for good biomass and enzyme yield and hence could be well employed in whey bioremediation.

Earthworms modify microbial community structure and accelerate maize stover decomposition during vermicomposting

In the present study, maize stover was vermicomposted with the epigeic earthworm Eisenia fetida. The results showed that, during vermicomposting process, the earthworms promoted decomposition of maize stover. Analysis of microbial communities of the vermicompost by high-throughput pyrosequencing showed more complex bacterial community structure in the substrate treated by the earthworms than that in the control group. The dominant microbial genera in the treatment with the earthworms were Pseudoxanthomonas, Pseudomonas, Arthrobacter, Streptomyces, Cryptococcus, Guehomyces, and Mucor. Compared to the control group, the relative abundance of lignocellulose degradation microorganisms increased. The results indicated that the earthworms modified the structure of microbial communities during vermicomposting process, activated the growth of lignocellulose degradation microorganisms, and triggered the lignocellulose decomposition.

Cold active β-galactosidase from Thalassospira sp. 3SC-21 to use in milk lactose hydrolysis: a novel source from deep waters of Bay-of-Bengal

The cold active β-galactosidase from psychrophilic bacteria accelerate the possibility of outperforming the current commercial β-galactosidase production from mesophilic sources. The present study is carried out to screen and isolate a cold active β-galactosidase producing bacterium from profound marine waters of Bay-of-Bengal and to optimize the factors for lactose hydrolysis in milk. Isolated bacterium 3SC-21 was characterized as marine psychrotolerant, halophile, gram negative, rod shaped strain producing an intracellular cold active β-galactosidase enzyme. Further, based upon the 16S rRNA gene sequence, bacterium 3SC-21 was identified as Thalassospira sp. The isolated strain Thalassospira sp. 3SC-21 had shown the enzyme activity between 4 and 20 °C at pH of 6.5 and the enzyme was completely inactivated at 45 °C. The statistical method, central composite rotatable design of response surface methodology was employed to optimize the hydrolysis of lactose and to reveal the interactions between various factors behind this hydrolysis. It was found that maximum of 80.18 % of lactose in 8 ml of raw milk was hydrolysed at pH of 6.5 at 20 °C in comparison to 40 % of lactose hydrolysis at 40 °C, suggesting that the cold active β-galactosidase from Thalassospira sp. 3SC-21 would be best suited for manufacturing the lactose free dairy products at low temperature.

A novel cold-active β-D-galactosidase from the Paracoccus sp. 32d--gene cloning, purification and characterization

Background

β-D-Galactosidases (EC 3.2.1.23) catalyze the hydrolysis of terminal non-reducing β-D-galactose residues in β-D-galactosides. Cold-active β-D-galactosidases have recently become a focus of attention of researchers and dairy product manufactures owing to theirs ability to: (i) eliminate of lactose from refrigerated milk for people afflicted with lactose intolerance, (ii) convert lactose to glucose and galactose which increase the sweetness of milk and decreases its hydroscopicity, and (iii) eliminate lactose from dairy industry pollutants associated with environmental problems. Moreover, in contrast to commercially available mesophilic β-D-galactosidase from Kluyveromyces lactis the cold-active counterparts could make it possible both to reduce the risk of mesophiles contamination and save energy during the industrial process connected with lactose hydrolysis.

Results

A genomic DNA library was constructed from soil bacterium Paracoccus sp. 32d. Through screening of the genomic DNA library on LB agar plates supplemented with X-Gal, a novel gene encoding a cold-active β-D-galactosidase was isolated. The in silico analysis of the enzyme amino acid sequence revealed that the β-D-galactosidase Paracoccus sp. 32d is a novel member of Glycoside Hydrolase Family 2. However, owing to the lack of a BGal_small_N domain, the domain characteristic for the LacZ enzymes of the GH2 family, it was decided to call the enzyme under study 'BgaL'. The bgaL gene was cloned and expressed in Escherichia coli using the pBAD Expression System. The purified recombinant BgaL consists of two identical subunits with a combined molecular weight of about 160 kDa. The BgaL was optimally active at 40°C and pH 7.5. Moreover, BgaL was able to hydrolyze both lactose and o-nitrophenyl-β-D-galactopyranoside at 10°C with K_m values of 2.94 and 1.17 mM and k_cat values 43.23 and 71.81 s^-1, respectively. One U of the recombinant BgaL would thus be capable hydrolyzing about 97% of the lactose in 1 ml of milk in 24 h at 10°C.

Conclusions

A novel bgaL gene was isolated from Paracoccus sp. 32d encoded a novel cold-active β-D-galactosidase. An E. coli expression system has enabled efficient production of soluble form of BgaL Paracoccus sp. 32d. The amino acid sequence analysis of the BgaL enzyme revealed notable differences in comparison to the result of the amino acid sequences analysis of well-characterized cold-active β-D-galactosidases belonging to Glycoside Hydrolase Family 2. Finally, the enzymatic properties of Paracoccus sp. 32d β-D-galactosidase shows its potential for being applied to development of a new industrial biocatalyst for efficient lactose hydrolysis in milk.

Enhanced β-galactosidase production from whey powder by a mutant of the psychrotolerant yeast Guehomyces pullulans 17-1 for hydrolysis of lactose

In order to isolate β-galactosidase overproducers of the psychrotolerant yeast Guehomyces pullulans 17-1, its cells were mutated by using nitrosoguanidine (NTG). One mutant (NTG-133) with enhanced β-galactosidase production was obtained. The mutant grown in the production medium with 30.0 g/l lactose and 2.0 g/l glucose could produce more β-galactosidase than the same mutant grown in the production medium with only 30.0 g/l lactose while β-galactosidase production by its wild type was sensitive to the presence of glucose in the medium. It was found that 40.0 g/l of the whey powder was the most suitable for β-galactosidase production by the mutant. After optimization of the medium and cultivation conditions, the mutant could produce 29.2 U/ml of total β-galactosidase activity within 132 h at the flask level while the mutant could produce 48.1 U/ml of total β-galactosidase activity within 144 h in 2-l fermentor. Over 77.1% of lactose in the whey powder (5.0% w/v) was hydrolyzed in the presence of the β-galactosidase activity of 280 U/g of lactose within 9 h while over 77.0% of lactose in the whey was hydrolyzed in the presence of β-galactosidase activity of 280 U/g of lactose within 6 h. This was the first time to show that the β-galactosidase produced by the psychrotolerant yeast could be used for hydrolysis of lactose in the whey powder and whey.

Enzymes in food processing: a condensed overview on strategies for better biocatalysts

Food and feed is possibly the area where processing anchored in biological agents has the deepest roots. Despite this, process improvement or design and implementation of novel approaches has been consistently performed, and more so in recent years, where significant advances in enzyme engineering and biocatalyst design have fastened the pace of such developments. This paper aims to provide an updated and succinct overview on the applications of enzymes in the food sector, and of progresses made, namely, within the scope of tapping for more efficient biocatalysts, through screening, structural modification, and immobilization of enzymes. Targeted improvements aim at enzymes with enhanced thermal and operational stability, improved specific activity, modification of pH-activity profiles, and increased product specificity, among others. This has been mostly achieved through protein engineering and enzyme immobilization, along with improvements in screening. The latter has been considerably improved due to the implementation of high-throughput techniques, and due to developments in protein expression and microbial cell culture. Expanding screening to relatively unexplored environments (marine, temperature extreme environments) has also contributed to the identification and development of more efficient biocatalysts. Technological aspects are considered, but economic aspects are also briefly addressed.

Identification, cloning and expression of a cold-active beta-galactosidase from a novel Arctic bacterium, Alkalilactibacillus ikkense

A novel, cold-active beta-galactosidase was isolated from an Arctic Gram-positive bacterium, Alkalilactibacillus ikkense. The corresponding gene was cloned and expressed as an active enzyme in Escherichia coli. Denaturing gel electrophoresis of both the native and the recombinant beta-galactosidase showed a monomeric molecular weight of 115-120 kDa. Analysis of the DNA sequence showed sequence similarity to known Glycosyl Hydrolase Family 2 beta-galactosidases from the genera Bacillus, Paenibacillus, Geobacillus, and Lactobacillus. The beta-galactosidase from this study was purified and shown to be highly active at low temperatures with more than 60% of its maximal activity maintained at 0 degrees C. The apparent optimal activity was observed at temperatures between 20 degrees C and 30 degrees C and at pH 8. The purified recombinant enzyme was stable without stabilizing agents for more than 100 hours at temperatures at and below 10 degrees C. At temperatures 40 degrees C and above, the beta-galactosidase was irreversibly inactivated within 10 minutes. When lactose was present in substantial amounts, the enzyme displayed transgalactosylation activity. Comparison of the beta-galactosidase with a commercially available enzyme showed that the conversion rate of the A. ikkense enzyme was approximately two-fold higher at temperatures between 0 degrees C and 20 degrees C.

An extracellular ice-binding glycoprotein from an Arctic psychrophilic yeast

A psychrophilic yeast was isolated from an Arctic pond and its culture supernatant showed ice-binding activity. This isolate, identified as Leucosporidium sp. based on an analysis of the D1/D2 and ITS regions of its ribosomal DNA, produced a secretory ice-binding protein (IBP). Yeast IBP was purified from the culture medium to near homogeneity by the ice affinity method and appeared to be glycosylated with a molecular mass of approximately 26 kDa. In addition, the yeast IBP was shown to have thermal hysteresis (TH) and recrystallization inhibition (RI) activities. The full-length cDNA for yeast IBP was determined and was found to encode a 261 amino acid protein with molecular weight of 26.8 kDa that includes an N-terminal signal peptide and one potential N-glycosylation site. The deduced protein showed high sequence identity with other IBPs and hypothetical IBPs from fungi, diatoms, and bacteria, clustering with a class of ice-active proteins.

Marine metagenomics: strategies for the discovery of novel enzymes with biotechnological applications from marine environments

Metagenomic based strategies have previously been successfully employed as powerful tools to isolate and identify enzymes with novel biocatalytic activities from the unculturable component of microbial communities from various terrestrial environmental niches. Both sequence based and function based screening approaches have been employed to identify genes encoding novel biocatalytic activities and metabolic pathways from metagenomic libraries. While much of the focus to date has centred on terrestrial based microbial ecosystems, it is clear that the marine environment has enormous microbial biodiversity that remains largely unstudied. Marine microbes are both extremely abundant and diverse; the environments they occupy likewise consist of very diverse niches. As culture-dependent methods have thus far resulted in the isolation of only a tiny percentage of the marine microbiota the application of metagenomic strategies holds great potential to study and exploit the enormous microbial biodiversity which is present within these marine environments.

Isolation and characterization of a metagenome-derived and cold-active lipase with high stereospecificity for (R)-ibuprofen esters

We report on the isolation and biochemical characterization of a novel, cold-active and metagenome-derived lipase with a high stereo-selectivity for pharmaceutically important substrates. The respective gene was isolated from a cosmid library derived from oil contaminated soil and designated lipCE. The deduced aa sequence indicates that the protein belongs to the lipase family l.3, with high similarity to Pseudomonas fluorescens lipases containing a C-terminal secretion signal for ABC dependent transport together with possible motifs for Ca(2+)-binding sites. The overexpressed protein revealed a molecular weight of 53.2kDa and was purified by refolding from inclusion bodies after expression in Escherichia coli. The optimum temperature of LipCE was determined to be 30 degrees C. However, the enzyme still displayed 28% residual activity at 0 degrees C and 16% at -5 degrees C. Calcium ions strongly increased activity and thermal stability of the protein. Further detailed biochemical characterization of the recombinant enzyme showed an optimum pH of 7 and that it retained activity in the presence of a range of metal ions and solvents. A detailed analysis of the enzyme's substrate spectrum with more than 34 different substrates indicated that the enzyme was able to hydrolyze a wide variety of substrates including the conversion of long chain fatty acid substrates with maximum activity for pNP-caprate (C(10)). Furthermore LipCE was able to hydrolyze stereo-selectively ibuprofen-pNP ester with a high preference for the (R) enantiomer of >91% ee and it demonstrated selectivity for esters of primary alcohols, whereas esters of secondary or tertiary alcohols were nearly not converted.

Mining enzymes from extreme environments

Current advances in metagenomics have revolutionized the research in fields of microbial ecology and biotechnology, enabling not only a glimpse into the uncultured microbial population and mechanistic understanding of possible biogeochemical cycles and lifestyles of extreme organisms but also the high-throughput discovery of new enzymes for industrial bioconversions. Nowadays, the genetic and enzymatic differences across the gradients from 'neutral and pristine' to 'extreme and polluted' environments are well documented. Yet, extremophilic organisms are possibly the least well understood because our ability to study and understand their metabolic potential has been hampered by our inability to isolate pure cultures. There are at least two obstacles for reaping the fruit of the microbial diversity of extremophiles: first, in spite of the recent progress in development of new culturing techniques most extremophiles cannot be cultured using traditional culturing technologies; and second, the problem of the very low biomass densities often occurs under the conditions hostile for life, which often do not yield enough DNA and reduces the effectiveness of cloning.

Molecular cloning and characterization of the gene encoding cold-active beta-galactosidase from a psychrotrophic and halotolerant Planococcus sp. L4

The gene bgaP encoding cold-active beta-galactosidase from a psychrotrophic and halotolerant Planococcus sp. L4 was cloned into Escherichia coli and sequenced. A sequence analysis of the DNA responsible for the BgaP gene revealed an open reading frame of 2031 bp encoding for a protein of 677 amino acid residues. The BgaP was heterologously expressed in E. coli and purified followed by Ni2+ affinity chromatography. The molecular mass of the native enzyme was approximately 156 kDa as determined by gel filtration. The results of sodium dodecyl sulfate-polyacrylamide gel electrophoresis and the deduced amino acid sequence of the BgaP indicated molecular masses of 78 and 77.311 kDa, respectively, suggesting that the BgaP is a dimer. The purified BgaP had an isoelectric point of 4.8 and exhibited maximal activity at 20 degrees C and pH 6.8 under the assay conditions used. The enzyme is particularly thermolabile, losing all activity in only 10 min at 45 degrees C. It was able to hydrolyze lactose as a substrate, as well as o-nitrophenyl-beta-D-galactopyranoside (ONPG); the Km values with ONPG and lactose were calculated to be 5.4 and 20.4 mM at 5 degrees C, respectively. The catalytic efficiencies of BagP for lactose at 5 and 20 degrees C had 14 and 47 times more than that of E. coli beta-galactosidase at 20 degrees C, respectively. Therefore, cold-active beta-galactosidase from the psychrotrophic and halotolerant Planococcus sp. L4 could conceivably be developed to fulfill the practical requirements to enable its use for lactose removal in milk and dairy products at low temperature or a reporter enzyme for psychrophilic genetic systems.

Purification and molecular characterization of cold-active β-galactosidase from Arthrobacter psychrolactophilus strain F2

In this study, we purified and molecularly characterized a cold-active beta-galactosidase from Arthrobacter psychrolactophilus strain F2. The purified beta-galactosidase from strain F2 exhibited high activity at 0 degrees C, and its optimum temperature and pH were 10 degrees C and 8.0, respectively. It was possible to inactivate the beta-galactosidase rapidly at 45 degrees C in 5 min. The enzyme was able to hydrolyze lactose as a substrate, as well as o-nitrophenyl-beta-D-galactopyranoside (ONPG), the Km values with ONPG and lactose being calculated to be 2.8 mM and 50 mM, respectively, at 10 degrees C. Moreover, the bglA gene encoding the beta-galactosidase of strain F2 was cloned and analyzed. The bglA gene consists of a 3,084-bp open reading frame corresponding to a protein of 1,028 amino acid residues. BglAp, the gene product derived from bglA, had several conserved regions for glycosyl hydrolase family 2, e.g., the glycosyl hydrolase 2 (GH2) sugar binding domain, GH2 acid-base catalyst, GH2 triosephosphate isomerase barrel domain, GH2 signature 1, and several other GH2 conserved regions. From these facts, we conclude that the beta-galactosidase from A. psychrolactophilus strain F2, which is a new member of glycosyl hydrolase family 2, is a cold-active enzyme that is extremely heat labile and could have advantageous applications in the food industry.