RESUMO
Prophages account for most of the genetic diversity among strains of a given bacterial species, and represent a latent source for the generation of virulent phages. In this work, a set of 30 commercial, collection and dairy-isolated Lactobacillus casei group strains were used. A species-specific PCR assay allowed a reclassification, mainly of strains previously considered Lactobacillus casei, into either Lactobacillus paracasei or Lactobacillus rhamnosus. All the strains were induced with mitomycin C, allowing direct recovering of phage DNA in 25 cases, which corroborates the widely occurrence of lysogeny on Lactobacillus genomes, including probiotic strains of Lactobacillus casei group. Ten out of 11 commercial strains studied contained prophages, evidencing the potential risks of their use at industrial scale. Strains were also induced by treatment with different concentrations of hydrogen peroxide but, however, this agent was not able to evidence a prophage release for any of the strains tested. According to a RAPD-PCR fingerprinting with M13, 1254 and G1 primers, most of the commercial strains presented a high degree of homology and, regarding BglII- and BamHI-restriction profiles of phage DNA, six of them harboured the same prophage. Surprisingly, both Lactobacillus paracasei ATCC 27092 and Lactobacillus paracasei ATCC 27139 shared a second prophage with both an INLAIN collection and a commercial Lactobacillus paracasei strains, whereas two collection strains shared a third one. On the other hand, mitomycin C-inducible prophages were detected only on about a half of the strains isolated from dairy products, which had (with only one exception) from moderate to high correlation coefficients according to RAPD-PCR fingerprinting. After induction, supernatants were filtered and tested against nine Lactobacillus strains of the set sensitive to previously assayed virulent phages, allowing isolation of two new virulent phages: Ñ iLp1308 and Ñ iLp84. Both phages were able to lyse all but one strains sensitive to previously assayed phage MLC-A.
Assuntos
Bacteriófagos/fisiologia , Produtos Fermentados do Leite , Indústria de Laticínios , Lactobacillus/genética , Lactobacillus/virologia , Lisogenia , Probióticos , Bacteriófagos/efeitos dos fármacos , Bacteriófagos/genética , Bacteriófagos/patogenicidade , Produtos Fermentados do Leite/microbiologia , Produtos Fermentados do Leite/virologia , DNA Bacteriano/genética , Lactobacillus/classificação , Lactobacillus/efeitos dos fármacos , Lacticaseibacillus casei/classificação , Lacticaseibacillus casei/genética , Lacticaseibacillus casei/virologia , Lacticaseibacillus rhamnosus/classificação , Lacticaseibacillus rhamnosus/genética , Lacticaseibacillus rhamnosus/virologia , Mitomicina/farmacologia , Inibidores da Síntese de Ácido Nucleico/farmacologia , FilogeniaRESUMO
Two greatly related Lactobacillus plantarum bacteriophages (named FAGK1 and FAGK2) were isolated from Kefir grains of different origins. Both phages belonged to the Siphoviridae family (morphotype B1) and showed similar dimensions for head and tail sizes. The host range of the two phages, using 36 strains as potential host strains, differed only in the phage reactivity against one of them. The phages showed latent periods of 30 min, burst periods of 80+/-10 min and burst size values of 11.0+/-1.0 PFU per infected cell as mean value. Identical DNA restriction patterns were obtained for both phages with PvuI, SalI, HindIII and MluI. The viral DNA apparently did not present extremes cos and the structural protein patterns presented four major bands (32.9, 35.7, 43.0 and 66.2 kDa). This study reports the first isolation of bacteriophages of Lb. plantarum from Kefir grains and adds further knowledge regarding the complex microbial community of this fermented milk.