Characteristics of a high-concentration-ammonium sulfate-requiring ammonia-oxidizing bacterium isolated from deodorization plants of chicken farms

A high-concentration-ammonium sulfate-requiring, ammonia-oxidizing bacterium, strain K1, was newly isolated from packed tower biological deodorization plants of chicken farms. The cells of strain K1 are rods (0.1-1.0 x 1.0-2.0 microm), gram negative, obligately aerobic, and nonmotile. Colonies (1-2 mm in diameter) on a plate culture are reddish, circular, and smooth. Intracytoplasmic membranes characteristic of nitrifying bacteria are present. The G+C content of the total DNA is 48.5 mol%. The similarity of 16S rRNA (%) to N. europaea ATCC 25978T (type strain) is 93.77%. This bacterium has a higher optimal growth temperature (35 degrees C) than is usually the case and tolerance up to 40 degrees C. The optimum concentration of ammonium sulfate in the medium is 303 mM, which should make it applicable for use in deodorization plants for enhancing the efficiency of deodorization. Phosphoglycerate kinase (PGK) and triosephosphate isomerase (TIM) were found to possess high specific activities (5700 and 4 x 10(5) U/mg, respectively) compared to the activities of these enzymes in strain ATCC 25978T (300 and 14 U/mg).     

Characteristics of an ammonia-oxidizing bacterium with a plasmid isolated from alkaline soils and its phylogenetic relationship

An ammonia-oxidizing bacterium, strain TCH716, was isolated from alkaline soil at Harbin city, China. The cells of strain TCH716 are lobate (0.8-1.5 x 1.0-2.0 microm), gram-negative, obligately aerobic, and nonmotile. Colonies (1-2 mm in diameter) on gellan gum plate culture are reddish, circular, and smooth. The G + C content of DNA is 54.78 mol%. Its percentage of 16S rRNA gene sequence similarity (%) to Nitrosolobus multiformis ATCC 25196T (type strain) is 98.56%. This bacterium has an optimal growth temperature and pH at 30 degrees C and 8.0-8.5, respectively. The concentration of ammonium sulfate in the HEPES medium for optimum growth of this bacterium is 38 mM. Strain TCH716 was found to have a plasmid (approximately 6.5 kbp) that possessed a plasmid-linked gene for sulfonamide resistance. Phosphoglycerate kinase, RubisCO and PEPC were found to possess high specific activities compared to the activities of these enzymes in strain ATCC 25978T. In identification of strain TCH716, both morphological characteristics (compartmentalized cells) and the phylogenetic relationship based on 16S rRNA gene sequence are important. Based on results obtained, strain TCH716 belongs to the genus Nitrosolobus, and designated as Nitrosolobus sp. TCH716.     

Probiotic and milk technological properties of Lactobacillus brevis

Two Lactobacillus brevis strains ATCC 8287 and ATCC 14869(T), were evaluated for their applicability as putative probiotics in dairy products. The strains expressed good in vitro adherence to human Caco-2 and Intestine 407 cells and tolerated well low pH, bile acids and pancreatic fluid under in vitro conditions. In antimicrobial activity assays, strain ATCC 8287 showed inhibitory properties toward selected potential harmful microorganisms, particularly against Bacillus cereus. Both L. brevis strains were resistant to vancomycin, which is typical for the genus Lactobacillus. The L. brevis strains were not able to acidify milk to yoghurt but were suitable as supplement strains in yoghurts. This was shown by producing a set of yoghurt products and analysing their rheological and sensory properties during a cold storage period of 28 days. Survival of the strains through human intestine was examined in 1-week feeding trials. Despite its human origin, L. brevis ATCC 14869(T) could not survive through the gastrointestinal (GI) tract, whereas L. brevis ATCC 8287 was detected in the faecal samples taken during and immediately after ingestion of the strain. In conclusion, L. brevis ATCC 8287 is a promising candidate as a probiotic supplement in dairy products.     

基于低拷贝质粒的高产紫色杆菌素谷氨酸棒杆菌的构建和发酵

该研究以公认安全(Generally Recognized as Safe,GRAS)的谷氨酸棒杆菌(Corynebacterium glutamicum)为宿主,构建高产紫色杆菌素的重组菌株。利用谷氨酸棒杆菌天然大质粒pTET3的复制与分配元件,构建了低拷贝质粒pOK12CG1,该质粒在谷氨酸棒杆菌中的拷贝数约为6拷贝/基因组,且与谷氨酸棒杆菌常用质粒pEC-XK99E和pXMJ19兼容。以低拷贝质粒pOK12CG1为骨架构建了携带紫色杆菌素合成操纵子(vioABCDE)的质粒pCGvio,并分别以谷氨酸棒杆菌标准株ATCC 13032和插入序列(Insertion Sequence,IS)元件删除株为宿主,构建了7株合成紫色杆菌素的重组菌株。通过初步筛选,发现基于低拷贝质粒的重组菌株ATCC13032/p CGvio,其紫色杆菌素产量(508.24 mg/L)高于基于中高拷贝质粒的重组菌株ATCC 13032/pECvio(376.16 mg/L),而基于低拷贝质粒的IS元件删除重组菌株ISDM023/pCGvio紫色杆菌素产量达到了610.13mg/L。进一步采用正交实验设计对重...     

Antagonism of Helicobacter pylori by bacteriocins of lactic acid bacteria

Antimicrobial activity of seven bacteriocins produced by lactic acid bacteria against Helicobacter pylori strains (ATCC 43504, Deutsche Sammlung von Mikroorganismen und Zellkulturen GmbH [DSM] 4867, DSM 9691, and DSM 10242) was investigated in vitro using a broth microdilution assay. The bacteriocins chosen for the study were nisin A; lacticins A164, BH5, JW3, and NK24; pediocin PO2; and leucocin K. Antimicrobial activity of the bacteriocins varied among the H. pylori strains tested, of which strain ATCC 43504 was the most tolerant. Among the bacteriocins tested, lacticins A164 and BH5 produced by Lactococcus lactis subsp. lactis A164 and L. lactis BH5, respectively, showed the strongest antibacterial activity against H. pylori strains. MICs of the lacticins against H. pylori strains, when assessed by the critical dilution micromethod, ranged from 0.097 to 0.390 mg/liter (DSM strains) or from 12.5 to 25 mg/liter (ATCC 43504), supporting the strain-dependent sensitivity of the pathogen. Pediocin PO2 was less active than the lacticins against four strains of H. pylori, and leucocin K was the least active peptide, with no inhibition toward H. pylori ATCC 43504. Anti-Helicobacter activity of lacticin A164 was dependent on initial inoculum size as well as concentration of the bacteriocin added.     

鼠李糖乳杆菌LR-ZB1107-01的安全性评价及其益生特性初步研究

从广州1月龄婴儿粪便中分离得一株乳酸菌,经鉴定为鼠李糖乳杆菌(Lactobacillus rhamnosus ZB1107-01),通过对该菌的溶血性、抗生素敏感性和动物经口急性毒理等安全性评价,并研究标准菌株与其对致病菌抑菌性、胃肠道液耐受性、肠道黏附性、疏水性和自聚力。结果表明:此菌无溶血性;对四环素、红霉素、氨基西林和卡那霉素等4种抗生素表现高敏感;小鼠经口急性毒理无毒,确定该菌株为食用安全菌。该菌可抑制金黄色葡萄球菌、大肠杆菌、单增李斯特菌的生长,抑菌效果与标准菌株ATCC7469相当。对人工模拟的胃肠道液有很好的耐受性,对pH2的人工胃液耐受性略强于标准菌株。黏附Caco-2细胞数与标准菌株相当。疏水性(48.6%)高于标准菌株(27.2%),自聚性与标准菌株相当。研究为鼠李糖乳杆菌LR-ZB1107-01在食品领域进行商业化应用提供理论依据。     

Identification, cloning, and characterization of a Sporobolomyces singularis beta-galactosidase-like enzyme involved in galacto-oligosaccharide production

Sporobolomyces singularis can be used as a biocatalyst in galacto-oligosaccharide production. We isolated 2-deoxy-D-glucose-resistant mutants of S. singularis ATCC 24193 and recovered a mutant that showed 10-fold higher beta-galactosidase-like activity than the parent strain and which was insensitive to catabolite repression. Thereafter, the beta-galactosidase-like enzyme was purified from the mutant and revealed to be a glycoprotein with both beta-glucosidase- and beta-galactosidase-like activity, the Michaelis-Menten constants of which for o-nitrophenyl-beta-D-galactopyranoside and p-nitrophenyl-beta-D-glucopyranoside were 5.40 and 1.96 mM, respectively, and the maximum velocities were 3.07 and 2.30 micromol/min per mg of protein, respectively. Its molecular mass was estimated to be 73.9 kDa by sodium dodecyl sulfate polyacrylamide gel electrophoresis and 146 kDa by gel filtration, suggesting that it has a homodimeric structure. We sequenced the N-terminus and internal peptides of this protein and isolated both a cDNA and a gene with degenerate primers. The gene, named bg l A, has 18 introns and 19 exons and encodes a polypeptide of 594 amino acids. The Bg l A protein was approximately 35% identical and 50% similar to plant beta-glucosidases belonging to family 1 glycosyl hydrolases, but with a unique 110-amino-acid sequence at the N-terminus. The beta-galactosidase-like enzyme (i.e., Bg l A protein) in S. singularis is a beta-glucosidase with high transgalactosidase activity.     

肠膜明串珠菌ATCC 12291蔗糖磷酸化酶的酶学性质及转糖苷分子改造

根据GenBank数据库公布的肠膜明串珠菌ATCC 12291中蔗糖磷酸化酶基因序列,构建重组表达质粒pQE-lmsp。在大肠杆菌Escherichia coli M15/pREP4中诱导表达,镍亲和层析纯化蛋白,进行酶学性质测定和重组酶转糖苷活性的研究。以蔗糖为底物对LMsp进行酶学性质分析,其最适温度和最适pH值分别为40 ℃和6.5;Km值和Vmax值分别为（34.16±1.219）mmol/L和（370.5±6.049）μmol/（mg·min）。当以葡萄糖-1-磷酸为供体时,对于大多数单糖及其糖醇类受体均具有转糖苷活性,尤其对L-阿拉伯糖具有75%的转化效率。然后通过对LMsp进行同源建模和氨基酸序列比对分析,进行分子改造,并比较酶学性质及转糖苷活性的变化。获得7 个单点和联合的突变体T180A、T219V、P236S、T180A-T219V、T180A-P236S、T219V-P236S、T180A-T219V-P236S,其中突变体T180A、P236S对L-山梨糖的转糖苷活性分别有13.7%和15%的提高。本研究通过对LMsp的研究,发现其具有良好的酸碱稳定性和对L-阿拉伯糖的高转糖苷活性,并且获得了对于L-山梨糖转糖苷活性提高的突变体,丰富了有关于蔗糖磷酸化酶的性质,并且对该酶的分子改造提供了经验依据。     

抗食源性病原菌细菌素的筛选及特性研究

目的 筛选一种抗食源性病原菌的细菌素,并对其稳定性进行研究.方法 以食源性病原菌Bacillus cereus ATCC 14579、Listeria monocytogenes LM201、Listeria monocytogenes LM605为指示菌,采用琼脂扩散法筛选细菌素产生菌,通过离子交换树脂法和高效液相色...     

产胞外多糖乳杆菌的筛选及多糖功能的研究

本论文从大连地区海产品消化腺中筛选产胞外多糖(EPS)的乳杆菌属菌株,并研究其所产EPS的功能特性,选出一株目标菌,对其EPS分离纯化,测定纯化后各多糖组分的相对分子量。获得EPS产量相对较高的菌株经16S r RNA序列测定鉴定为Lactobacillus plantarum subsp.plantarum-4,Lactobacillus plantarum-12,Lactobacillus plantarumsubsp.plantarum-49;对3株植物乳杆菌及其EPS进行清除DPPH自由基的测定,Lactobacillus plantarum-12的EPS浓度为0.5 mg/mL时,清除率为48.82±3.88%,显著高于另外2株菌(p0.05);测定植物乳杆菌的EPS抑制E.coli ATCC25922在HT-29细胞上的粘附效果,Lactobacillus plantarum-12的EPS浓度为0.2mg/mL时,抑制率为78.23%±2.46%,显著高于另外两株菌(p0.05);Lactobacillus plantarum-12的EPS可显著抑制E·coli ATCC25922刺激HT-29细胞产生IL-8(p0.05)。Lactobacillus plantarum-12的EPS经DEAE-Sepharose Fast Flow离子交换柱、Sepharose CL-6B凝胶柱和Sephacryl HR S200凝胶柱层析分离得到两组分,测定两组分的相对分子质量分别为8.5×10~4 u和7.4×10~4 u。     

Paenibacillus tyraminigenes sp. nov. isolated from Myeolchi-jeotgal, a traditional Korean salted and fermented anchovy

A bacterial strain H3029, a gram-positive, rod-shaped, oxidase-negative, endospore-forming bacterium that characteristically produces tyramine from tyrosine, was isolated from a Myeolchi-jeotgal, a traditional Korean salted and fermented anchovy (Engraulis japonicus). The H3029 strain showed a high ability to produce 4140 microg/ml of tyramine from the culture broth containing 5000 microg/ml tyrosine. On the other hand, the strain produced a relatively low level of other putrefactive amines, at 973 microg/ml of putrescine and 147 microg/ml of cadaverine from the media, with each 5000 microg/ml of ornithine hydrochloride and lysine hydrochloride. The H3029 strain produced no detectable level of histamine (detection limit of 4 microg/ml) from the media containing 5000 microg/ml of histidine hydrochloride. Meanwhile, tyramine, the main product of the strain, showed the antimicrobial activity at the level of over 1 mg/disk against Staphylococcus aureus by agar diffusion test, and the mutagenicity in Ames test at 0.1 mg/plate using Salmonella typhimurium TA98 and TA1535. On the basis of the polyphasic taxonomic study, the H3029(T) strain was assigned a novel species of the genus Paenibacillus as Paenibacillus tyraminigenes sp. nov. The type strain of which is strain H3029(T) (=KCTC 10694BP(T)).     

Inactivation effect of an 18-T pulsed magnetic field combined with other technologies on Escherichia coli

The inactivation effect of 18 T pulsed magnetic fields in combination with selected non-thermal technologies was studied on Escherichia coli ATCC 11775. The bacteria were subjected to a treatment of either ultrasound (20 kHz, 70 W, 242 μm), high hydrostatic pressure (207 MPa, 5 min), pulsed electric field (6.25 kV/cm, 5.6 ms), or anti-microbials (Nisin 77.5 mg/l, lysozyme 1 mg/ml) and 50 magnetic field pulses (18 T, 30 μs). No additional inactivation or cell damage due to exposure to the pulsed magnetic field at 42°C was observed.     

Enhancement of the activity of novobiocin against Escherichia coli by lactoferrin

The activity of novobiocin against Escherichia coli ATCC 25922 and three E. coli strains that were isolated from cases of bovine mastitis was determined in timekill studies in the presence of bovine lactoferrin. Lactoferrin alone did not affect the growth of any of the strains of E. coli. A combination of 1.0 mg/ml of lactoferrin and novobiocin at 1/16x minimum inhibitory concentration (MIC) was bactericidal for E. coli ATCC 25922. When the concentration was increased to 3.0 mg/ml of lactoferrin, novobiocin was bactericidal at 1/64x MIC. Among the mastitis strains tested, 6789 and 6806 were more susceptible to killing by novobiocin than was strain 6800. Strains 6789 and 6806 were killed when treated with novobiocin concentrations of 2, 1/2, and 1/4x MIC. When these strains were also treated with lactoferrin at 3.0 mg/ml, there was a bacteriostatic effect at novobiocin concentrations of 1/8 and 1/16x MIC for strains 6789 and 6800. Strain 6806 appeared to be more susceptible to the combination of lactoferrin and novobiocin as was evidenced by a bactericidal effect over the 24-h testing period. The combination treatment with cephapirin and lactoferrin showed that there was a synergistic bactericidal effect against all of the E. coli strains tested. These studies indicate that lactoferrin can potentiate the activity of antibiotics against Gram-negative bacteria.     

Transformation of bisphenol A and alkylphenols by ammonia-oxidizing bacteria through nitration

Transformation of bisphenol A (BPA) by ammonia-oxidizing bacteria (AOB) Nitrosomonas europaea ATCC 19718 was investigated. On the basis of the ultraperformance liquid chromatography (UPLC) coupled to quadrupole time-of-flight mass spectrometry (Q-TOF MS) and nuclear magnetic resonance analysis, we found N. europaea could transform BPA into nitro- and dinitro-BPA, suggesting that abiotic nitration between the biogenic nitrite and BPA played a major role in the transformation of BPA in the batch AOB system. Nitrite concentrations, temperature, and pH values were the major factors to influence the reaction rate. Furthermore, the yeast estrogenic screening assay showed that the formed nitro- and dinitro-BPA had much less estrogenic activity as compared with its parent compound BPA. Similar reactions of abiotic nitration were considered for 4-n-nonylphenol (nNP) and 4-n-octylphenol (nOP) since nitro-nNP and nitro-nOP were detected by UPLC-Q-TOF MS. In addition, results from the local wastewater treatment plant (WWTP) showed the occurrence of nitro-BPA and dinitro-BPA during the biological treatment process and in the effluent, indicating that nitration of BPA is also a pathway for removal of BPA. Results of this study provided implication that AOB in the WWTPs might contribute to removal of selected endocrine-disrupting compounds (EDCs) through abiotic nitritation.     

Supercritical fluid extraction of antioxidant and antimicrobial compounds from Laurus nobilis L. Chemical and functional characterization

Extraction of laurel leaves by using supercritical carbon dioxide was carried out on a supercritical fluid (SF) pilot-scale plant. The extraction pressure and temperature were set to 250 bar and 60°C, respectively, using a 4% of ethanol as modifier. The employed apparatus, owing to a two-stage separation, allowed us to obtain two different fractions (F1 and F2), whose antioxidant and antimicrobial activities were investigated. Two different methods, β-carotene bleaching test and DPPH^• free radical–scavenging assay, were carried out to determine the antioxidant activity. Moreover, antimicrobial activity of laurel fractions was tested against Staphylococcus aureus ATCC 25923, Bacillus subtilis ATCC 6633, Pseudomonas aeruginosa ATCC 10145, Escherichia coli ATCC 11775, Candida albicans ATCC 60193 and Aspergillus niger ATCC 16404. Minimum inhibitory concentration (MIC) and minimal bactericidal and fungicidal concentration (MBC) were obtained. Both fractions showed a similar antioxidant activity, although it was slightly higher for the fraction recovered in separator 2. However, antimicrobial activity against the microorganisms tested was only found when fraction 2 was used. Staphylococcus aureus was the most sensitive microorganism to this fraction, with maximal inhibition zones (25 mm) and the lowest MBC values (1.25 mg/ml), whereas the least susceptible was the fungi Aspergillus niger. In order to determine the compounds responsible for the antimicrobial activity, fraction 2 was analysed by GC–MS; results obtained showed that most of the compounds identified in the supercritical extract have been previously described to show antimicrobial activity; among them, the major compound found in the supercritical extract corresponded to a sesquiterpene lactone of the germacrolide type (6-epi-desacetyllaurenobiolide) previously described in laurel.     

Ribulose-1,5-bisphosphate carboxylase/oxygenase from an ammonia-oxidizing bacterium, Nitrosomonas sp. K1: purification and properties

The ammonia-oxidizing chemoautotrophic Nitrosomonas sp. strain K1 exhibited marked ribulose-1,5-bisphosphate carboxylase (RubisCO) activity. The RubisCO [EC 4.1.1.39] was purified as an electrophoretically homogeneous protein. The molecular mass of the enzyme was estimated to be about 460 kDa by gel filtration, and it consists of two subunits [large (L): 52.2 kDa; small (S): 13.3 kDa] as demonstrated by SDS-PAGE. This confirmed that the enzyme has an L(8)S(8) structure. The K(m) values of the enzyme for RuBP, NaHCO3, and Mg2+ were estimated to be 0.112, 0.415, and 1.063 mM, respectively. The optimum pH and temperature for its activity were approximately 7.0 and 45 degrees C. The enzyme was stable up to 45 degrees C and in a pH range from 7.0-9.0 (4 degrees C, 48 h). The enzyme activity was inhibited by Cu2+, Hg2+, N-ethylmaleimide, p-chloromercuribenzoate, and SDS (0.1 mM). The activity was also inhibited by ammonium sulfate at high concentrations (38-303 mM) but the stability of the enzyme showed no inhibition at the same ammonium sulfate concentrations. The N-terminal amino acid sequences of the large and small subunits are AIKTYQAGVKEYRQTYW QPDYVPL and AIQAYHLTKKYETFSYLPQM, respectively.     

Characterisation of an antiviral pediocin-like bacteriocin produced by Enterococcus faecium

The bacteriocin-producing strain Enterococcus faecium ST5Ha was isolated from smoked salmon and identified by biomolecular techniques. Ent. faecium ST5Ha produces a pediocin-like bacteriocin with activity against several lactic acid bacteria, Listeria spp. and some other human and food pathogens, and remarkably against HSV-1 virus. Bacteriocin ST5Ha was produced at high levels in MRS broth at 30 °C and 37 °C, reaching a maximum production of 1.0 × 10⁹ AU/ml, checked against Listeria ivanovii ATCC19119 as target strain and surrogate of pathogenic strain Listeria monocytogenes. The molecular weight of bacteriocin ST5Ha was estimated to be 4.5 kDa according to tricine-SDS-PAGE data. Ent. faecium ST5Ha harbors a 1.044 kb chromosomal DNA fragment fitting in size to that of pediocin PA-1/AcH. In addition, the sequencing of bacteriocin ST5Ha gene indicated 99% of DNA homology to pediocin PA-1/AcH. The combined application of low levels (below MIC) of ciprofloxacin and bacteriocin ST5Ha resulted in a synergetic effect in the inhibition of target strain L. ivanovii ATCC19119. Bacteriocin ST5Ha displayed antiviral activity against HSV-1, an important human pathogen, with a selectivity index of 173. To the best of our knowledge, this is the first report on Ent. faecium as a potential producer of pediocin-like bacteriocin with antiviral activity.     

斜叶黄檀精油功能活性

本文主要测定斜叶黄檀精油中的挥发性成分、多酚和黄酮含量,采用体外抗氧化评价斜叶黄檀精油的清除DPPH和ABTS自由基能力、总还原力和总抗氧化能力,以金黄色葡萄球菌(G+)、化脓性链球菌(G+)、大肠杆菌(G-)、铜绿假单胞菌(G-)、鼠伤寒沙门氏菌(G-)以及白色念珠菌(真菌)为待测菌,评价精油的抑菌效果,通过对酪氨酸酶的抑制活性评价精油抑制黑色素的形成能力。结果表明斜叶黄檀精油在浓度为0.18 mg/mL时,对DPPH和ABTS自由基的清除能力均达到70%左右,在浓度分别为0.18 mg/mL和1 mg/mL时,总还原力和总抗氧化能力的吸光度值均达到0.4以上。对金黄色葡萄球菌、化脓性链球菌以及白色念珠菌的抑菌圈直径分别为:12.83、11.50和10.25 mm,呈现中敏程度的抑制性,但对三种革兰氏阴性菌无明显的抑制效果。精油对酪氨酸酶的抑制活性要强于阳性对照熊果苷,在浓度为0.1 mg/mL抑制率将近90%。本文得出斜叶黄檀精油有较好的抗氧化活性、抑制革兰氏阳性菌和真菌以及抑制酪氨酸酶活性,比较完善的介绍了斜叶黄檀精油的功能活性。     

Two kinds of ammonia-oxidizing bacteria isolated from biologically deodorizing plants in cold district

Two kinds of ammonia-oxidizing bacteria isolated from biologically deodorizing plants in cold districts in Japan were identified as Nitrosomonas sp. IWT202 and Nitrosomonas sp. IWT514. The optimum pHs for growth were 8.0 (IWT202) and 7.5 (IWT514). Although rockwool samples for isolation were collected from the same plants, the optimum temperature for growth of strain IWT202 (37 degrees C) differed from that of strain IWT514 (30 degrees C). The bacteria had a higher (IWT202, 37 degrees C) and lower (IWT514, 20 degrees C) growth temperature than is usually the case. Both strains were shown to differ completely in regard to the effect of the ammonium sulfate concentration in the medium for a 20 degrees C culture and 30 degrees C culture. The inoculation of these bacteria provides the possibility of recovering ammonia-oxidizing activity, when the ammonia-oxidizing activity is lowered in biological deodorizing plants in cold districts. It seems that these strains are suitable for application to deodorization.     

Performance of Lactobacillus helveticus Spontaneous Phage-resistant Mutants in Hard Cheese Production

From the strain Lactobacillus helveticus ATCC 15807, a total of 66 clones were isolated using the lytic phages hv and ATCC 15807-B1. Phenotypic parameters related to their phage resistance capacity (efficiency of plaquing, phage resistance stability, lysogeny and adsorption rates) were determined. The morphological, biochemical (sugar fermentation patterns) and technological (acidifying power, proteolytic activity and slime production) characteristics of the isolates were also studied. Phage resistance stability was a variable property among the isolates but a high level of resistance was exhibited as quantified by the efficiency of plaquing. Furthermore, a total absence of acquired lysogeny was demonstrated. The phage-resistant variants were completely or partially unable to bind phages and did not show differences with Lb. helveticus ATCC 15807 in their biochemical characteristics. However, the technological properties (acidifying powers and proteolytic activities) were heterogeneously distributed among the mutants. The variant RB1-28 (isolated under selective pressure of the phage ATCC 15807-B1) was evaluated for the technological performance in Sardo cheese production in comparison with Lb. helveticus ATCC 15807. There were no significant differences between the two types of cheeses, taking in consideration physicochemical parameters (proteolysis level, dry matter, total and soluble proteins, moisture), microbiological counts or sensory analysis. These phage-resistant variants could be employed in starter strain rotation programs for cheesemaking.