Isolation and molecular characterization of chitinase-deficient Bacillus licheniformis strains capable of deproteinization of shrimp shell waste to obtain highly viscous chitin

Enzymatic approaches in the bioprocessing of shellfish wastes

Several tonnes of shellfish wastes are generated globally due to the mass consumption of shellfish meat from crustaceans like prawn, shrimp, lobster, crab, Antarctic krill, etc. These shellfish wastes are a reservoir of valuable by-products like chitin, protein, calcium carbonate, and pigments. In the present scenario, these wastes are treated chemically to recover chitin by the chitin and chitosan industries, using hazardous chemicals like HCl and NaOH. Although this process is efficient in removing proteins and minerals, the unscientific dumping of harmful effluents is hazardous to the ecosystem. Stringent environmental laws and regulations on waste disposal have encouraged researchers to look for alternate strategies to produce near-zero wastes on shellfish degradation. The role of enzymes in degrading shellfish wastes is advantageous yet has not been explored much, although it produces bioactive rich protein hydrolysates with good quality chitin. The main objective of the review is to discuss the potential of various enzymes involved in shellfish degradation and their opportunities and challenges over chemical processes in chitin recovery.

Potentialities and Characterization of an Antifungal Chitinase Produced by a Halotolerant Bacillus licheniformis

The chitinases are gaining much attention based on their role in the defense against pathogen attacks and harmful insects. The partially chitinase produced by Bacillus licheniformis strain J24 exhibited a large antifungal spectrum, and the highest activity was obtained toward Fusarium species in vitro on PDA and in vivo on corn seeds. The chitinase was inducible by the presence of autoclaved Fusarium conidia in the medium culture and it was active at 70 °C and pH 7 and not affected by the tested chemical agents EDTA and SDS. The nucleotide and amino acid sequences encoding chitinase showed the close phylogenetic relation with chitinase from Bacillus paralicheniformis species. Based on the analysis of the putative domain active, the described chitinase from strain J24 was belonging to the GH family-18 and the novelty of its structure was revealed. Here the combination of functional and structural antifungal extremely chitinase proves its importance in biotechnology area.

Sustainable and eco-friendly strategies for shrimp shell valorization

Among the seafood used globally, shellfish consumption is in great demand. The utilization of these shellfish such as prawn/shrimp has opened a new market for the utilization of the shellfish wastes. Considering the trends on the production of wealth from wastes, shrimp shell wastes seem an important resource for the generation of high value products when processed on the principles of a biorefinery. In recent years, various chemical strategies have been tried to valorize the shrimp shell wastes, which required harsh chemicals such as HCl and NaOH for demineralization (DM) and deproteination (DP) of the shrimp wastes. Disposal of chemicals by the chitin and chitosan industries into the aquatic bodies pose harm to the aquatic flora and fauna. Thus, there has been intensive efforts to develop safe and sustainable technologies for the management of shrimp shell wastes. This review provides an insight about environmentally-friendly methods along with biological methods to valorize the shrimp waste compared to the strategies employing concentrated chemicals. The main objective of this review article is to explain the utilization shrimp shell wastes in a productive manner such that it would be offer environment and economic sustainability. The application of valorized by-products developed from the shrimp shell wastes and physical methods to improve the pretreatment process of shellfish wastes for valorization are also highlighted in this paper.

Determinación microbiológica y molecular mediante PCR en tiempo real de dos bacterias del género Bacillus de interés agro biotecnológico

Se efectuó la comparación de curvas de crecimiento a diferentes rangos de pH, salinidad y temperatura, además se determinó el tamaño, forma y posición de endospora de dos diferentes cepas del género Bacillus. Para la identificación molecular se realizó la extracción de ácidos nucleicos, utilizando el kit High Pure PCR Template Preparation Kit de Roche® y posteriormente se analizaron las curvas de amplificación producto de la PCR en Tiempo Real. Se realizaron cinéticas de crecimiento a cada uno de los cultivos de bacterias durante 72 horas y se analizaron estadísticamente las curvas mediante los métodos estadísticos ANOVA y Tukey para determinar significancia (p˂0.001). El análisis factorial para la variable “temperatura” no mostró una diferencia significativa entre cepas y tampoco con los valores fijados (28, 32, 37 °C), la variable “pH” si presentó una interacción con valores (p<0.0001) entre cepas; la variable “salinidad” también presentó diferencia significativa entre cepas y con sus respectivas interacciones. En el análisis del área bajo la curva, la variable “temperatura” no mostró diferencia significativa, mientras que las variables “pH y salinidad” presentaron valores correspondientes a (p<0.0001). Para la determinación molecular, se analizaron las curvas de amplificación, confirmando la presunción bioquímica de la cepa BM como B. megaterium mediante el análisis del gen phaC, así como también se pudo corroborar que la cepa BL corresponde a B. licheniformis al analizar el gen lchAA. La cinética bacteriana permitió establecer las horas clave para el análisis del crecimiento, confirmando que las características analizadas corresponden a especies pertenecientes a la familia Bacillaceae, con aplicación como controladores biológicos en la agricultura.

Chitin extraction from shrimp waste by liquid fermentation using an alkaline protease-producing strain, Brevibacillus parabrevis

In this study, an extracellular protease, but no chitinolytic enzyme-producing strain, Brevibacillus parabrevis TKU046, has been isolated and analyzed for the deproteinization testing of shrimp waste by liquid fermentation. Deproteinization assays of shrimp waste with this microbe showed 95% protein removal after 4 days fermentation. The efficiency of chitin extraction by B. parabrevis TKU046 on wastes of three shrimp species were also investigated in which the highest deproteinization was found on cooked tiger shrimp shell. Infrared spectra (IR) of the obtained chitin displayed characteristic profiles for chitin. The culture supernatant released after fermentation greatly exhibited growth enhancing effect on Lactobacillus rhamnosus. In addition, B. parabrevis TKU046 protease was isolated and determined the characteristics. The molecular mass of B. parabrevis TKU046 protease was determined as 32 kDa and 34 kDa, respectively, by SDS-PAGE and HPLC. Overall, the findings provide strong support for the potential candidacy of this enzyme as an effective and eco-friendly alternative to the conventional chemicals used for the deproteinization of shrimp heads in the chitin processing industry, as well as the production of prebiotics to be used in the nutraceutical industry.

Isolation and characterization of a Bacillus amyloliquefaciens strain with zearalenone removal ability and its probiotic potential

Zearalenone (ZEN) is a non-steroidal estrogenic mycotoxin produced by Fusarium species, which has been shown to be associated with reproductive disorders in livestock, and to a lesser extent with hyperoestrogenic syndromes in humans. The aim of this study was to characterize a Bacillus amyloliquefaciens strain with ZEN removal ability. A pure culture of a strain designated LN isolated from moldy corn samples showed a high ZEN removal capability. Based on microscopic observations, biochemical characteristics, and phylogenetic analysis of the 16S rRNA gene sequence, LN was identified as B. amyloliquefaciens. After incubation of B. amyloliquefaciens LN in Luria-Bertani (LB) medium containing 3.5 ppm of ZEN, the ZEN concentration fell below the detection limit within 24 h. In ZEN-contaminated corn meal medium, B. amyloliquefaciens LN decreased ZEN concentration by 92% after 36 h of incubation. In phosphate-buffered saline (PBS) containing 5 ppm of ZEN, B. amyloliquefaciens LN reduced the ZEN concentration from 5 ppm to 3.28 ppm immediately after coming into contact with ZEN, and further reduced the ZEN concentration to 0.36 ppm after 4 h of incubation. The amounts of ZEN adsorbed by the cells of B. amyloliquefaciens LN did not increase with the extension of incubation time, indicating that B. amyloliquefaciens LN not only possessed ZEN adsorption ability, but also exhibited the ability to degrade ZEN. In addition, B. amyloliquefaciens LN was non-hemolytic, non-enterotoxin producing, and displayed probiotic characteristics including acidic tolerance, bile salt tolerance, and anti-pathogenic activities. These findings suggest that B. amyloliquefaciens LN has a potential to be used as a feed additive to reduce the concentrations of ZEN in feedstuffs.

Microbial Degradation of Lobster Shells to Extract Chitin Derivatives for Plant Disease Management

Biodegradation of lobster shells by chitinolytic microorganisms are an environment safe approach to utilize lobster processing wastes for chitin derivation. In this study, we report degradation activities of two microbes, "S223" and "S224" isolated from soil samples that had the highest rate of deproteinization, demineralization and chitinolysis among ten microorganisms screened. Isolates S223 and S224 had 27.3 and 103.8 protease units mg-1 protein and 12.3 and 11.2 μg ml-1 of calcium in their samples, respectively, after 1 week of incubation with raw lobster shells. Further, S223 contained 23.8 μg ml-1 of N-Acetylglucosamine on day 3, while S224 had 27.3 μg ml-1 on day 7 of incubation with chitin. Morphological observations and 16S rDNA sequencing suggested both the isolates were Streptomyces. The culture conditions were optimized for efficient degradation of lobster shells and chitinase (∼30 kDa) was purified from crude extract by affinity chromatography. The digested lobster shell extracts induced disease resistance in Arabidopsis by induction of defense related genes (PR1 > 500-fold, PDF1.2 > 40-fold) upon Pseudomonas syringae and Botrytis cinerea infection. The study suggests that soil microbes aid in sustainable bioconversion of lobster shells and extraction of chitin derivatives that could be applied in plant protection.

Pilot-scale chitin extraction from shrimp shell waste by deproteination and decalcification with bacterial enrichment cultures

Extraction of chitin from mechanically pre-purified shrimp shells can be achieved by successive NaOH/HCl treatment, protease/HCl treatment or by environmentally friendly fermentation with proteolytic/lactic acid bacteria (LAB). For the last mentioned alternative, scale-up of shrimp shell chitin purification was investigated in 0.25 L (F1), 10 L (F2), and 300 L (F3) fermenters using an anaerobic, chitinase-deficient, proteolytic enrichment culture from ground meat for deproteination and a mixed culture of LAB from bio-yoghurt for decalcification. Protein removal in F1, F2, and F3 proceeded in parallel within 40 h at an efficiency of 89-91 %. Between 85 and 90 % of the calcit was removed from the shells by LAB in another 40 h in F1, F2, and F3. After deproteination of shrimp shells in F3, spent fermentation liquor was re-used for a next batch of 30-kg shrimp shells in F4 (300 L) which eliminated 85.5 % protein. The purity of the resulting chitin was comparable in F1, F2, F3, and F4. Viscosities of chitosan, obtained after chitin deacetylation and of chitin, prepared biologically or chemically in the laboratory, were much higher than those of commercially available chitin and chitosan.

The two putative comS homologs of the biotechnologically important Bacillus licheniformis do not contribute to competence development

In Bacillus subtilis, natural genetic competence is subject to complex genetic regulation and quorum sensing dependent. Upon extracellular accumulation of the peptide-pheromone ComX, the membrane-bound sensor histidine kinase ComP initiates diverse signaling pathways by activating-among others-DegQ and ComS. While DegQ favors the expression of extracellular enzymes rather than competence development, ComS is crucial for competence development as it prevents proteolytic degradation of ComK, the key transcriptional activator of all genes required for the uptake and integration of DNA. In Bacillus licheniformis, ComX/ComP sensed cell density negatively influences competence development, suggesting differences from the quorum-sensing-dependent control mechanism in Bacillus subtilis. Here, we show that each of six investigated strains possesses both of two different, recently identified putative comS genes. When expressed from an inducible promoter, none of the comS candidate genes displayed an impact on competence development neither in B. subtilis nor in B. licheniformis. Moreover, disruption of the genes did not reduce transformation efficiency. While the putative comS homologs do not contribute to competence development, we provide evidence that the degQ gene as for B. subtilis negatively influences genetic competency in B. licheniformis.

Unravelling the genetic basis for competence development of auxotrophic Bacillus licheniformis 9945A strains

Bacterial natural genetic competence – well studied in Bacillus subtilis – enables cells to take up and integrate extracellularly supplied DNA into their own genome. However, little is known about competence development and its regulation in other members of the genus, although DNA uptake machineries are routinely encoded. Auxotrophic Bacillus licheniformis 9945A derivatives, obtained from repeated rounds of random mutagenesis, were long known to develop natural competence. Inspection of the colony morphology and extracellular enzyme secretion of two of these derivatives, M28 and M18, suggested that regulator genes are collaterally hit. M28 emerged as a 14 bp deletion mutant concomitantly displaying a shift in the reading frame of degS that encodes the sensor histidine kinase, which is part of the molecular switch that directs cells to genetic competence, the synthesis of extracellular enzymes or biofilm formation, while for M18, sequencing of the suspected gene revealed a 375 bp deletion in abrB, encoding the major transition state regulator. With respect to colony morphology, enzyme secretion and competence development, both of the mutations, when newly generated on the wild-type B. licheniformis 9945A genetic background, resulted in phenotypes resembling M28 and M18, respectively. All of the known naturally competent B. licheniformis representatives, hitherto thoroughly investigated in this regard, carry mutations in regulator genes, and hence genetic competence observed in domesticated strains supposedly results from deregulation.

Generation of biologically contained, readily transformable, and genetically manageable mutants of the biotechnologically important Bacillus pumilus

Bacillus pumilus mutants were generated by targeted deletion of a set of genes eventually facilitating genetic handling and assuring biological containment. The well-defined and stable mutants do not form functional endospores due to the deletion of yqfD, an essential sporulation gene; they are affected in DNA repair, as ΔuvrBA rendered them UV hypersensitive and, thus, biologically contained; they are deficient for the uracil phosphoribosyl-transferase (Δupp), allowing for 5-fluorouracil-based counterselection facilitating rapid allelic exchanges; and they are readily transformable due to the deletion of the restrictase encoding locus (ΔhsdR) of a type I restriction modification system. Vegetative growth as well as extracellular enzyme production and secretion are in no case affected. The combination of such gene deletions allows for development of B. pumilus strains suited for industrial use and further improvements.

The direct repeat sequence upstream of Bacillus chitinase genes is cis-acting elements that negatively regulate heterologous expression in E. coli

To explore the influence of the direct repeat sequence (DRS) in Bacillus chitinase genes on heterogonous expression in Escherichia coli, we cloned and sequenced the entire open reading frame (ORF) and upstream sequences of the chitinase B (chiB) and chitinase MY75 (chiMY75) from Bacillus thuringiensis and Bacillus licheniformis. A pair of 8-bp DRS was found upstream of each chi gene. Chi ORFs with a series of truncated DRS were cloned and transformed into E. coli XL-Blue. The activity of the transformants without the DRS were significantly higher in chitinase assays than transformants containing the DRS. SDS-PAGE showed that part and full deletion of the DRS increased chi gene expression by approximately 1.7 and 3.8-fold, respectively. Northern blotting revealed deletion of the DRS regions increased chiB and chiMY75 mRNA expression. Specific binding of DNA-binding factors in the E. coli cell lyaste was observed to both the chiB and chiMY75 promoter regions and DRS elements. This is the first investigation to demonstrate that heterologous expression of Bacillus chi genes in E. coli is negatively regulated by their upstream DRS regions, which act as cis-acting elements.

Chitinase production by Bacillus thuringiensis and Bacillus licheniformis: their potential in antifungal biocontrol

Thirty bacterial strains were isolated from the rhizosphere of plants collected from Egypt and screened for production of chitinase enzymes. Bacillus thuringiensis NM101-19 and Bacillus licheniformis NM120-17 had the highest chitinolytic activities amongst those investigated. The production of chitinase by B. thuringiensis and B. licheniformis was optimized using colloidal chitin medium amended with 1.5% colloidal chitin, with casein as a nitrogen source, at 30°C after five days of incubation. An enhancement of chitinase production by the two species was observed by addition of sugar substances and dried fungal mats to the colloidal chitin media. The optimal conditions for chitinase activity by B. thuringiensis and B. licheniformis were at 40°C, pH 7.0 and pH 8.0, respectively. Na(+), Mg(2+), Cu(2+), and Ca(2+) caused enhancement of enzyme activities whereas they were markedly inhibited by Zn(2+), Hg(2+), and Ag(+). In vitro, B. thuringiensis and B. licheniformis chitinases had potential for cell wall lysis of many phytopathogenic fungi tested. The addition of B. thuringiensis chitinase was more effective than that of B. licheniformis in increasing the germination of soybean seeds infected with various phytopathogenic fungi.

Overexpression and characterization of thermostable chitinase from Bacillus atrophaeus SC081 in Escherichia coli

The chitinase-producing strain SC081 was isolated from Korean traditional soy sauce and identified as Bacillus atrophaeus based on a phylogenetic analysis of the 16S rDNA sequence and a phenotypic analysis. A gene encoding chitinase from B. atrophaeus SC081 was cloned in Escherichia coli and was named SCChi-1 (GQ360078). The SCChi-1 nucleotide sequences were composed of 1788 base pairs and 596 amino acids, which were 92.6, 89.6, 89.3, and 78.9% identical to those of Bacillus subtilis (ABG57262), Bacillus pumilus (ABI15082), Bacillus amyloliquefaciens (ABO15008), and Bacillus licheniformis (ACF40833), respectively. A recombinant SCChi-1 containing a hexahistidine tag at the amino- terminus was constructed, overexpressed, and purified in E. coli to characterize SCChi-1. H(6)SCChi-1 revealed a hydrolytic band on zymograms containing 0.1% glycol chitin and showed the highest lytic activity on colloidal chitin and acidic chitosan. The optimal temperature and pH for chitinolytic activity were 50°C and pH 8.0, respectively.

Genetic improvement of Bacillus licheniformis strains for efficient deproteinization of shrimp shells and production of high-molecular-mass chitin and chitosan

By targeted deletion of the polyglutamate operon (pga) in Bacillus licheniformis F11, a derivative form, F11.1 (Δpga), was obtained that, along with lacking polyglutamate (PGA) formation, displayed enhanced proteolytic activities. The phenotypic properties were maintained in a strain in which the chiBA operon was additionally deleted: F11.4 (ΔchiBA Δpga). These genetically modified strains, carrying the Δpga deletion either alone (F11.1) or together with the ΔchiBA (F11.4) deletion, were used in fermentations (20-liter scale) aiming at the deproteinization of shrimp shells in order to obtain long-chain chitin. After chemical deacetylation, the resulting chitosan samples were analyzed by nuclear magnetic resonance spectroscopy, size exclusion chromatography, and viscometry and compared to a chitosan preparation that was produced in parallel by chemical methods by a commercial chitosan supplier (GSRmbH). Though faint lipid impurities were present in the fermented polysaccharides, the viscosity of the material produced with the double-deletion mutant F11.4 (Δpga ΔchiBA) was higher than that of the chemically produced and commercially available samples (Cognis GmbH). Thus, enhanced proteolytic activities and a lack of chitinase activity render the double mutant F11.4 a powerful tool for the production of long-chain chitosan.

Facilitation of direct conditional knockout of essential genes in Bacillus licheniformis DSM13 by comparative genetic analysis and manipulation of genetic competence

The genetic manageability of the biotechnologically important Bacillus licheniformis is hampered due to its poor transformability, whereas Bacillus subtilis efficiently takes up DNA during genetic competence, a quorum-sensing-dependent process. Since the sensor histidine kinase ComP, encoded by a gene of the quorum-sensing module comQXPA of B. licheniformis DSM13, was found to be inactive due to an insertion element within comP, the coding region was exchanged with a functional copy. Quorum sensing was restored, but the already-poor genetic competence dropped further. The inducible expression of the key regulator for the transcription of competence genes, ComK, in trans resulted in highly competent strains and facilitated the direct disruption of genes, as well as the conditional knockout of an essential operon. As ComK is inhibited at low cell densities by a proteolytic complex in which MecA binds ComK and such inhibition is antagonized by the interaction of MecA with ComS (the expression of the latter is controlled by cell density in B. subtilis), we performed an in silico analysis of MecA and the hitherto unidentified ComS, which revealed differences for competent and noncompetent strains, indicating that the reduced competence possibly is due to a nonfunctional coupling of the comQXPA-encoded quorum module and ComK. The obtained increased genetic tractability of this industrial workhorse should improve a wide array of scientific investigations.

Efficient decomposition of shrimp shell waste using Bacillus cereus and Exiguobacterium acetylicum

Two bacterial cultures were isolated and tested for degradation of shrimp shell waste. According to morphological examination, physiological tests, and applied molecular techniques, isolates were identified as Bacillus cereus and Exiguobacterium acetylicum. Both strains were cultivated separately in flasks with 100 mL of shrimp shell waste broth (3% of washed, dried and ground shrimp shell waste in tap water, pH 7.0) at 37 degrees C. At determined periods of time, deproteinization and demineralization of residuals were measured. Fermentation of 3% shell waste with B. cereus indicated 97.1% deproteinization and 95% demineralization. For E. acetylicum, the level of deproteinization and demineralization was 92.8 and 92%, respectively. Protein content was reduced from 18.7 to 5.3% with B. cereus and to 7.3% with E. acetylicum. No additional supplements were used during the fermentation of shell waste. B. cereus strain showed higher efficacy in decomposition of shell waste and was used for large-scale fermentation in 12 L of 10% shrimp shell waste broth. Incubation of bacteria with shell waste during 14 days at 37 degrees C resulted in 78.6% deproteinization and 73% demineralization. High activity of isolated cultures in decomposition of shrimp shell waste suggests broad potential for application of these bacteria in environmentally friendly approaches to chitin extraction from chitin-rich wastes.

An organic-solvent-tolerant esterase from thermophilic Bacillus licheniformis S-86

A thermophile, halotolerant and organic-solvent-tolerant esterase producer Bacillus sp. S-86 strain previously isolated was found to belong to Bacillus licheniformis species through morphological, biochemical, 16S rRNA gene sequence analyses and rDNA intergenic spacers amplification (ITS-PCR). The strain can grow at 55 degrees C in presence of C2-C7 alkanols (log P=-0.86 to 2.39), and NaCl concentrations up to 15% (w/v). This bacterium showed optimal growth and esterase production at 50 degrees C. Two different molecular weight esterase activities were detected in zymographic assays. PMSF inhibited type I esterase activity, showing no inhibitory effect on type II esterase activity. B. licheniformis S-86 was able to grow in presence of hydroxylic organic-solvents like propan-2-ol, butan-1-ol and 3-methylbutan-1-ol. At a sub-lethal concentration of these solvents (392 mmoll(-1) propan-2-ol; 99 mmol l(-1) butan-1-ol, 37 mmol l(-1) 3-methylbutan-1-ol), adequate to produce 50% cell growth inhibition at 50 degrees C, an increment between 1.9 and 2.3 times was observed in type I esterase production, and between 2.2 and 3.1 times in type II esterase production.

Chitin purification from shrimp wastes by microbial deproteination and decalcification

Chitin was purified from Penaeus monodon and Crangon crangon shells using a two-stage fermentation process with anaerobic deproteination followed by decalcification through homofermentative lactic acid fermentation. Deproteinating enrichment cultures from sewage sludge and ground meat (GM) were used with a proteolytic activity of 59 and 61 mg N l(-1) h(-1) with dried and 26 and 35 mg N l(-1) h(-1) with wet P. monodon shells. With 100 g wet cells of proteolytic bacteria per liter, protein removal was obtained in 42 h. An anaerobic spore-forming bacterium HP1 was isolated from enrichment GM. Its proteolytic activity was 76 U ml(-1) compared to 44 U ml(-1) of the consortium. Glucose was fermented with Lactobacillus casei MRS1 to lactic acid. At a pH of 3.6, calcium carbonate of the shells was solubilised. After deproteination and decalcification of P. monodon or C. crangon shells, the protein content was 5.8% or 6.7%, and the calcium content was 0.3% or 0.4%, respectively. The viscosity of the chitin from P. monodon and C. crangon was 45 and 135 mPa s, respectively, whereas purchased crab shell chitin (practical grade) had a viscosity of 21 mPa s, indicating a higher quality of biologically purified chitin.

Targeted deletion of genes encoding extracellular enzymes in Bacillus licheniformis and the impact on the secretion capability

The general secretory pathway is routinely concerned with a multitude of extracellular enzymes. By eliminating obstructive competitors the export machinery may transport larger quantities of remaining proteins under circumstances in which the secretion machinery is fully loaded. Hence, in this study, genes encoding efficiently expressed but dispensable exoenzymes were knocked out in Bacillus licheniformis MD1. Single, double, and triple mutants with deletions of celA, chiA, and amyB, respectively, were generated via in vivo recombination by making use of a vector with a temperature sensitive origin of replication. Overexpression of a heterologous amylase gene on a multi-copy plasmid, a common scenario in biotechnological processes, resulted in an articulate reduction of chromosomally encoded extracellular enzyme activities indicating that the secretion machinery works to capacity in such transformants. Deletion mutants with the expression plasmid displayed enhanced amylase activities compared to the strain with the wild type genetic background. In addition, the chromosomally encoded protease activity was clearly higher in transformants with deletions.

Targeted deletion of the uvrBA operon and biological containment in the industrially important Bacillus licheniformis

From a Bacillus licheniformis wild type as well as a defined asporogenous derivative, stable UV hypersensitive mutants were generated by targeted deletion of the uvrBA operon, encoding highly conserved key components of the nucleotide excision repair. Comparative studies, which included the respective parental strains, revealed no negative side effects of the deletion, neither on enzyme secretion nor on vegetative propagation. Thus, the uvrBA locus proved to be a useful deletion target for achieving biological containment in this industrially exploited bacterium. In contrast to recA mutants, which also display UV hypersensitivity, further strain development via homologous recombination techniques will be still possible in such uvr mutants.