High-resolution proteome maps of Bacillus licheniformis cells growing in minimal medium.

Bacillus licheniformis is an important host for the industrial production of enzymes mainly because of its ability to secrete large amounts of protein. We analyzed the proteome of B. licheniformis cells growing in a minimal medium. Beside the cytosolic proteome, the membrane and the extracellular proteome were studied. We could identify 1470 proteins; 1168 proteins were classified as cytosolic proteins, 195 proteins with membrane-spanning domains were classified as membrane proteins, and 107 proteins, with either putative signals peptides or flagellin-like sequences, were classified as secreted proteins. The identified proteins were grouped into functional categories and used to reconstruct cellular functions and metabolic pathways of growing B. licheniformis cells. The largest group was proteins with functions in basic metabolic pathways such as carbon metabolism, amino acid and nucleotide synthesis and synthesis of fatty acids and cofactors. Many proteins detected were involved in DNA replication, transcription, and translation. Furthermore, a high number of proteins employed in the transport of a wide variety of compounds were found to be expressed in the cells. All MS data have been deposited in the ProteomeXchange with identifier PXD000791 (http://proteomecentral.proteomexchange.org/dataset/PXD000791).

Advances in protease engineering for laundry detergents.

Proteases are essential ingredients in modern laundry detergents. Over the past 30 years, subtilisin proteases employed in the laundry detergent industry have been engineered by directed evolution and rational design to tailor their properties towards industrial demands. This comprehensive review discusses recent success stories in subtilisin protease engineering. Advances in protease engineering for laundry detergents comprise simultaneous improvement of thermal resistance and activity at low temperatures, a rational strategy to modulate pH profiles, and a general hypothesis for how to increase promiscuous activity towards the production of peroxycarboxylic acids as mild bleaching agents. The three protease engineering campaigns presented provide in-depth analysis of protease properties and have identified principles that can be applied to improve or generate enzyme variants for industrial applications beyond laundry detergents.

Cell physiology of the biotechnological relevant bacterium Bacillus pumilus-an omics-based approach.

Members of the species Bacillus pumilus get more and more in focus of the biotechnological industry as potential new production strains. Based on exoproteome analysis, B. pumilus strain Jo2, possessing a high secretion capability, was chosen for an omics-based investigation. The proteome and metabolome of B. pumilus cells growing either in minimal or complex medium was analyzed. In total, 1542 proteins were identified in growing B. pumilus cells, among them 1182 cytosolic proteins, 297 membrane and lipoproteins and 63 secreted proteins. This accounts for about 43% of the 3616 proteins encoded in the B. pumilus Jo2 genome sequence. By using GC-MS, IP-LC/MS and H NMR methods numerous metabolites were analyzed and assigned to reconstructed metabolic pathways. In the genome sequence a functional secretion system including the components of the Sec- and Tat-secretion machinery was found. Analysis of the exoproteome revealed secretion of about 70 proteins with predicted secretion signals. In addition, selected production-relevant genome features such as restriction modification systems and NRPS clusters of B. pumilus Jo2 are discussed.

A proteomic view of cell physiology of the industrial workhorse Bacillus licheniformis.

Bacillus licheniformis is known for its high protein secretion capacity and is being applied extensively as a host for the industrial production of enzymes such as proteases and amylases. In its natural environment as well as in fermentation processes the bacterium is often facing adverse conditions such as oxidative or osmotic stress or starvation for nutrients. During the last years detailed proteome and transcriptome analyses have been performed to study the adaptation of B. licheniformis cells to various stresses (heat, ethanol, oxidative or salt stress) and starvation conditions (glucose, nitrogen or phosphate starvation). A common feature of the response to all tested conditions is the downregulation of many genes encoding house-keeping proteins and, consequently, a reduced synthesis of the corresponding proteins. Induction of the general stress response (σ(B) regulon) is only observed in cells subjected to heat, ethanol or salt stress. This paper summarizes our current knowledge on general and specific stress and starvation responses of this important industrial bacterium. The importance of selected marker genes and proteins for the monitoring and optimization of B. licheniformis based fermentation processes is discussed.

Developing a new production host from a blueprint: Bacillus pumilus as an industrial enzyme producer.

BACKGROUND: Since volatile and rising cost factors such as energy, raw materials and market competitiveness have a significant impact on the economic efficiency of biotechnological bulk productions, industrial processes need to be steadily improved and optimized. Thereby the current production hosts can undergo various limitations. To overcome those limitations and in addition increase the diversity of available production hosts for future applications, we suggest a Production Strain Blueprinting (PSB) strategy to develop new production systems in a reduced time lapse in contrast to a development from scratch.To demonstrate this approach, Bacillus pumilus has been developed as an alternative expression platform for the production of alkaline enzymes in reference to the established industrial production host Bacillus licheniformis. RESULTS: To develop the selected B. pumilus as an alternative production host the suggested PSB strategy was applied proceeding in the following steps (dedicated product titers are scaled to the protease titer of Henkel's industrial production strain B. licheniformis at lab scale): Introduction of a protease production plasmid, adaptation of a protease production process (44%), process optimization (92%) and expression optimization (114%). To further evaluate the production capability of the developed B. pumilus platform, the target protease was substituted by an α-amylase. The expression performance was tested under the previously optimized protease process conditions and under subsequently adapted process conditions resulting in a maximum product titer of 65% in reference to B. licheniformis protease titer. CONCLUSIONS: In this contribution the applied PSB strategy performed very well for the development of B. pumilus as an alternative production strain. Thereby the engineered B. pumilus expression platform even exceeded the protease titer of the industrial production host B. licheniformis by 14%. This result exhibits a remarkable potential of B. pumilus to be the basis for a next generation production host, since the strain has still a large potential for further genetic engineering. The final amylase titer of 65% in reference to B. licheniformis protease titer suggests that the developed B. pumilus expression platform is also suitable for an efficient production of non-proteolytic enzymes reaching a final titer of several grams per liter without complex process modifications.

Bacillus pumilus reveals a remarkably high resistance to hydrogen peroxide provoked oxidative stress.

Bacillus pumilus is characterized by a higher oxidative stress resistance than other comparable industrially relevant Bacilli such as B. subtilis or B. licheniformis. In this study the response of B. pumilus to oxidative stress was investigated during a treatment with high concentrations of hydrogen peroxide at the proteome, transcriptome and metabolome level. Genes/proteins belonging to regulons, which are known to have important functions in the oxidative stress response of other organisms, were found to be upregulated, such as the Fur, Spx, SOS or CtsR regulon. Strikingly, parts of the fundamental PerR regulon responding to peroxide stress in B. subtilis are not encoded in the B. pumilus genome. Thus, B. pumilus misses the catalase KatA, the DNA-protection protein MrgA or the alkyl hydroperoxide reductase AhpCF. Data of this study suggests that the catalase KatX2 takes over the function of the missing KatA in the oxidative stress response of B. pumilus. The genome-wide expression analysis revealed an induction of bacillithiol (Cys-GlcN-malate, BSH) relevant genes. An analysis of the intracellular metabolites detected high intracellular levels of this protective metabolite, which indicates the importance of bacillithiol in the peroxide stress resistance of B. pumilus.

Stress responses of the industrial workhorse Bacillus licheniformis to osmotic challenges.

The Gram-positive endospore-forming bacterium Bacillus licheniformis can be found widely in nature and it is exploited in industrial processes for the manufacturing of antibiotics, specialty chemicals, and enzymes. Both in its varied natural habitats and in industrial settings, B. licheniformis cells will be exposed to increases in the external osmolarity, conditions that trigger water efflux, impair turgor, cause the cessation of growth, and negatively affect the productivity of cell factories in biotechnological processes. We have taken here both systems-wide and targeted physiological approaches to unravel the core of the osmostress responses of B. licheniformis. Cells were suddenly subjected to an osmotic upshift of considerable magnitude (with 1 M NaCl), and their transcriptional profile was then recorded in a time-resolved fashion on a genome-wide scale. A bioinformatics cluster analysis was used to group the osmotically up-regulated genes into categories that are functionally associated with the synthesis and import of osmostress-relieving compounds (compatible solutes), the SigB-controlled general stress response, and genes whose functional annotation suggests that salt stress triggers secondary oxidative stress responses in B. licheniformis. The data set focusing on the transcriptional profile of B. licheniformis was enriched by proteomics aimed at identifying those proteins that were accumulated by the cells through increased biosynthesis in response to osmotic stress. Furthermore, these global approaches were augmented by a set of experiments that addressed the synthesis of the compatible solutes proline and glycine betaine and assessed the growth-enhancing effects of various osmoprotectants. Combined, our data provide a blueprint of the cellular adjustment processes of B. licheniformis to both sudden and sustained osmotic stress.

Size unlimited markerless deletions by a transconjugative plasmid-system in Bacillus licheniformis.

Conjugative shuttle vectors of the pKVM series, based on an IncP transfer origin and the pMAD vector with a temperature sensitive replication were constructed to establish a markerless gene deletion protocol for Bacilli without natural competence such as the exoenzyme producer Bacillus licheniformis. The pKVM plasmids can be conjugated to strains of B. licheniformis and B. subtilis. For chromosomal gene deletion, regions flanking the target gene are fused and cloned in a pKVM vector prior to conjugative transfer from Escherichia coli to B. licheniformis. Appropriate markers on the vector backbone allow for the identification of the integration at the target locus and thereafter the vector excision, both events taking place via homologous recombination. The functionality of the deletion system was demonstrated with B. licheniformis by a markerless 939 bp in-frame deletion of the yqfD gene and the deletion of a 31 kbp genomic segment carrying a PBSX-like prophage.

Redirecting catalysis from proteolysis to perhydrolysis in subtilisin Carlsberg.

Enzyme promiscuity describes the ability of biocatalysts to catalyze conversions beyond their natural reactions. Enzyme engineering to promote side reactions is attractive for synthetic and industrial applications. For instance, a subtilisin Carlsberg protease variant (T58A/L216W) catalyzes in addition to its proteolytic activity the generation of peroxycarboxylic acids from corresponding esters in the presence of hydrogen peroxide. In the current study we used a semi-rational design approach to shift the specificity of subtilisin Carlsberg towards production of peroxycarboxylic acid. Among other identified amino acid substitutions, position Gly165 in the S1 binding pocket provided insights in subtilisin Carlsberg's promiscuity by promoting ester perhydrolysis. Catalytic constants of subtilisin Carlsberg for perhydrolysis of methyl-propionate, methyl-butyrate and methyl-pentanoate were increased up to 3.5-, 5.4- and 5.5-fold, respectively, while proteolysis was decreased up to 100-fold for N-succinyl-Ala-Ala-Pro-Phe-p-nitroanilide substrate (suc-AAPF-pNA).

The response of Bacillus licheniformis to heat and ethanol stress and the role of the SigB regulon.

The heat and ethanol stress response of Bacillus licheniformis DSM13 was analyzed at the transcriptional and/or translational level. During heat shock, regulons known to be heat-induced in Bacillus subtilis 168 are upregulated in B. licheniformis, such as the HrcA, SigB, CtsR, and CssRS regulon. Upregulation of the SigY regulon and of genes controlled by other extracytoplasmic function (ECF) sigma factors indicates a cell-wall stress triggered by the heat shock. Furthermore, tryptophan synthesis enzymes were upregulated in heat stressed cells as well as regulons involved in usage of alternative carbon and nitrogen sources. Ethanol stress led to an induction of the SigB, HrcA, and CtsR regulons. As indicated by the upregulation of a SigM-dependent protein, ethanol also triggered a cell wall stress. To characterize the SigB regulon of B. licheniformis, we analyzed the heat stress response of a sigB mutant. It is shown that the B. licheniformis SigB regulon comprises additional genes, some of which do not exist in B. subtilis, such as BLi03885, encoding a hypothetical protein, the Na/solute symporter gene BLi02212, the arginase homolog-encoding gene BLi00198 and mcrA, encoding a protein with endonuclease activity.

Surface charge engineering of a Bacillus gibsonii subtilisin protease.

In proteins, a posttranslational deamidation process converts asparagine (Asn) and glutamine (Gln) residues into negatively charged aspartic (Asp) and glutamic acid (Glu), respectively. This process changes the protein net charge affecting enzyme activity, pH optimum, and stability. Understanding the principles which affect these enzyme properties would be valuable for protein engineering in general. In this work, three criteria for selecting amino acid substitutions of the deamidation type in the Bacillus gibsonii alkaline protease (BgAP) are proposed and systematically studied in their influence on pH-dependent activity and thermal resistance. Out of 113 possible surface amino acids, 18 (11 Asn and 7 Gln) residues of BgAP were selected and evaluated based on three proposed criteria: (1) The Asn or Gln residues should not be conserved, (2) should be surface exposed, and (3) neighbored by glycine. "Deamidation" in five (N97, N253, Q37, Q200, and Q256) out of eight (N97, N154, N250, N253, Q37, Q107, Q200, and Q256) amino acids meeting all criteria resulted in increased proteolytic activity. In addition, pH activity profiles of the variants N253D and Q256E and the combined variant N253DQ256E were dramatically shifted towards higher activity at lower pH (range of 8.5-10). Variant N253DQ256E showed twice the specific activity of wild-type BgAP and its thermal resistance increased by 2.4 °C at pH 8.5. These property changes suggest that mimicking surface deamidation by substituting Gln by Glu and/or Asn by Asp might be a simple and fast protein reengineering approach for modulating enzyme properties such as activity, pH optimum, and thermal resistance.

Secretory production of an FAD cofactor-containing cytosolic enzyme (sorbitol-xylitol oxidase from Streptomyces coelicolor) using the twin-arginine translocation (Tat) pathway of Corynebacterium glutamicum.

Carbohydrate oxidases are biotechnologically interesting enzymes that require a tightly or covalently bound cofactor for activity. Using the industrial workhorse Corynebacterium glutamicum as the expression host, successful secretion of a normally cytosolic FAD cofactor-containing sorbitol-xylitol oxidase from Streptomyces coelicolor was achieved by using the twin-arginine translocation (Tat) protein export machinery for protein translocation across the cytoplasmic membrane. Our results demonstrate for the first time that, also for cofactor-containing proteins, a secretory production strategy is a feasible and promising alternative to conventional intracellular expression strategies.

Reengineering of subtilisin Carlsberg for oxidative resistance.

Mild bleaching conditions by in situ production of hydrogen peroxide or peroxycarboxylic acid is attractive for pulp, textile, and cosmetics industries. The enzymatic generation of chemical oxidants is often limited by enzyme stability. The subtilisin Carlsberg variant T58A/L216W/M221 is a promiscuous protease that was improved in producing peroxycarboxylic acids. In the current article, we identified two amino acid positions (Trp216 and Met221) that are important for the oxidative resistance of subtilisin Carlsberg T58A/L216W/M221. Site-saturation mutagenesis at positions Trp216 and Met221, which are located close to the active site, resulted in variants M4 (T58/W216M/M221) and M6 (T58A/W216L/M221C). Variants M4 (T58/W216M/M221) and M6 (T58A/W216L/M221C) have a 2.6-fold (M4) and 1.5-fold (M6) increased oxidative resistance and 1.4-fold increased kcat values for peroxycarboxylic acid formation, compared with wild-type subtilisin Carlsberg.

Increasing activity and thermal resistance of Bacillus gibsonii alkaline protease (BgAP) by directed evolution.

Bacillus gibsonii Alkaline Protease (BgAP) is a recently reported subtilisin protease exhibiting activity and stability properties suitable for applications in laundry and dish washing detergents. However, BgAP suffers from a significant decrease of activity at low temperatures. In order to increase BgAP activity at 15°C, a directed evolution campaign based on the SeSaM random mutagenesis method was performed. An optimized microtiter plate expression system in B. subtilis was established and classical proteolytic detection methods were adapted for high throughput screening. In parallel, the libraries were screened for increased residual proteolytic activity after incubation at 58°C. Three iterative rounds of directed BgAP evolution yielded a set of BgAP variants with increased specific activity (K(cat)) at 15°C and increased thermal resistance. Recombination of both sets of amino acid substitutions resulted finally in variant MF1 with a 1.5-fold increased specific activity (15°C) and over 100 times prolonged half-life at 60°C (224 min compared to 2 min of the WT BgAP). None of the introduced amino acid substitutions were close to the active site of BgAP. Activity-altering amino acid substitutions were from non-charged to non-charged or from sterically demanding to less demanding. Thermal stability improvements were achieved by substitutions to negatively charged amino acids in loop areas of the BgAP surface which probably fostered ionic and hydrogen bonds interactions.

Fluorescent assay for directed evolution of perhydrolases.

Directed evolution offers opportunities to improve promiscuous activities of hydrolases in rounds of diversity generation and high-throughput screening. In this article, we developed and validated a screening platform to improve the perhydrolytic activity of proteases and likely other hydrolases (e.g., lipases or esterases). Key was the development of a highly sensitive fluorescent assay (sensitivity in the µM range) based on 3-carboxy-7-hydroxycoumarin (HCC) formation. HCC is released through an hypobromite-mediated oxidation of 7-(4'-aminophenoxy)-3-carboxycoumarin (APCC), which enables for the first time a continuous measurement of peroxycarboxylic acid formation with a standard deviation of 11% in microtiter plates with a wide pH range window (5-9). As example, subtilisin Carlsberg was subjected to site saturation mutagenesis at position G165, yielding a variant T58A/G165L/L216W with 5.4-fold increased k(cat) for perhydrolytic activity compared with wild type.

An efficient transformation method for Bacillus subtilis DB104.

Bacillus subtilis strains are used for extracellular expression of enzymes (i.e., proteases, lipases, and cellulases) which are often engineered by directed evolution for industrial applications. B. subtilis DB104 represents an attractive directed evolution host since it has a low proteolytic activity and efficient secretion. B. subtilis DB104 is hampered like many other Bacillus strains by insufficient transformation efficiencies (≤10(3) transformants/µg DNA). After investigating five physical and chemical transformation protocols, a novel natural competent transformation protocol was established for B. subtilis DB104 by optimizing growth conditions and histidine concentration during competence development, implementing an additional incubation step in the competence development phase and a recovery step during the transformation procedure. In addition, the influence of the amount and size of the transformed plasmid DNA on transformation efficiency was investigated. The natural competence protocol is "easy" in handling and allows for the first time to generate large libraries (1.5 × 10(5) transformants/µg plasmid DNA) in B. subtilis DB104 without requiring microgram amounts of DNA.

Asymmetric synthesis of D-glyceric acid by an alditol oxidase and directed evolution for enhanced oxidative activity towards glycerol.

Glycerol as a by-product of biodiesel production is an attractive precursor for producing d-glyceric acid. Here, we demonstrate the successful production of d-glyceric acid based on glycerol via glyceraldehyde in a two-step enzyme reaction with the FAD-dependent alditol oxidase from Streptomyces coelicolor A3(2). The hydrogen peroxide generated in the reaction can be used in detergent, food, and paper industry. In order to apply the alditol oxidase in industry, the enzyme was subjected to protein engineering. Different strategies were used to enhance the substrate specificity towards glycerol. Initial attempts based on rational protein design in the active site region were found unsuccessful to increase activity. However, through directed evolution, an alditol oxidase double mutant (V125M/A244T) with 1.5-fold improved activity for glycerol was found by screening 8,000 clones. Further improvement of activity was achieved by combinatorial experiments, which led to a quadruple mutant (V125M/A244T/V133M/G399R) with 2.4-fold higher specific activity towards glycerol compared to the wild-type enzyme. Through studying the effects of mutations created, we were able to understand the importance of certain amino acids in the structure of alditol oxidase, not only for conferring enzymatic structural stability but also with respect to their influence on oxidative activity.

The peroxide stress response of Bacillus licheniformis.

The oxidative stress response of Bacillus licheniformis after treatment with hydrogen peroxide was investigated at the transcriptome, proteome and metabolome levels. In this comprehensive study, 84 proteins and 467 transcripts were found to be up or downregulated in response to the stressor. Among the upregulated genes were many that are known to have important functions in the oxidative stress response of other organisms, such as catalase, alkylhydroperoxide reductase or the thioredoxin system. Many of these genes could be grouped into putative regulons by genomic mining. The occurrence of oxidative damage to proteins was analyzed by a 2-DE-based approach. In addition, we report the induction of genes with hitherto unknown functions, which may be important for the specific oxidative stress response of B. licheniformis. The genes BLi04114 and BLi04115, that are located adjacent to the catalase gene, were massively induced during peroxide stress. Furthermore, the genes BLi04207 and BLi04208, which encode proteins homologous to glyoxylate cycle enzymes, were also induced by peroxide. Metabolomic analyses support the induction of the glyoxylate cycle during oxidative stress in B. licheniformis.

Hydrolysis of polyethyleneterephthalate by p-nitrobenzylesterase from Bacillus subtilis.

From a screening on agar plates with bis(benzoyloxyethyl) terephthalate (3PET), a Bacillus subtilis p-nitrobenzylesterase (BsEstB) was isolated and demonstrated to hydrolyze polyethyleneterephthalate (PET). PET-hydrolase active strains produced clearing zones and led to the release of the 3PET hydrolysis products terephthalic acid (TA), benzoic acid (BA), 2-hydroxyethyl benzoate (HEB), and mono-(2-hydroxyethyl) terephthalate (MHET) in 3PET supplemented liquid cultures. The 3PET-hydrolase was isolated from non-denaturating polyacrylamide gels using fluorescein diacetate (FDA) and identified as BsEstB by LC-MS/MS analysis. BsEstB was expressed in Escherichia coli with C-terminally fused StrepTag II for purification. The tagged enzyme had a molecular mass of 55.2 kDa and a specific activity of 77 U/mg on p-nitrophenyl acetate and 108 U/mg on p-nitrophenyl butyrate. BsEstB was most active at 40°C and pH 7.0 and stable for several days at pH 7.0 and 37°C while the half-life times decreased to 3 days at 40°C and only 6 h at 45°C. From 3PET, BsEstB released TA, MHET, and BA, but neither bis(2-hydroxyethyl) terephthalate (BHET) nor hydroxyethylbenzoate (HEB). The kcat values decreased with increasing complexity of the substrate from 6 and 8 (s-1) for p-nitrophenyl-acetate (4NPA) and p-nitrophenyl-butyrate (4NPB), respectively, to 0.14 (s-1) for bis(2-hydroxyethyl) terephthalate (BHET). The enzyme hydrolyzed PET films releasing TA and MHET with a concomitant decrease of the water-contact angle (WCA) from 68.2°±1.7° to 62.6°±1.1° due to formation of novel hydroxyl and carboxyl groups. These data correlated with a fluorescence emission intensity increase seen for the enzyme treated sample after derivatization with 2-(bromomethyl)naphthalene.

Genetic control of amadori product degradation in Bacillus subtilis via regulation of frlBONMD expression by FrlR.

Bacillus subtilis is capable of degrading fructosamines. The phosphorylation and the cleavage of the resulting fructosamine 6-phosphates is catalyzed by the frlD and frlB gene products, respectively. This study addresses the physiological importance of the frlBONMD genes (formerly yurPONML), revealing the necessity of their expression for growth on fructosamines and focusing on the complex regulation of the corresponding transcription unit. In addition to the known regulation by the global transcriptional regulator CodY, the frl genes are repressed by the convergently transcribed FrlR (formerly YurK). The latter causes repression during growth on substrates other than fructosamines. Additionally, we identified in the first intergenic region of the operon an FrlR binding site which is centrally located within a 38-bp perfect palindromic sequence. There is genetic evidence that this sequence, in combination with FrlR, contributes to the remarkable decrease in the transcription downstream of the first gene of the frl operon.