| Congresso Brasileiro de Microbiologia 2023 | Resumo: 1105-1 | ||||
Resumo:The growth of lactic acid bacteria (LAB) during the manufacture of fermented foods is desirable because these bacteria improve hygienic characteristics and sensory profile of the product and increase its conservation time. The main LAB used in the dairy industry in Argentina is Streptococcus thermophilus, which is susceptible to bacteriophage attack. Among all the known tools used by bacteria to evade phages, CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats) systems are particularly important in S. thermophilus. Consequently, CRISPR systems have been extensively studied in strains of S. thermophilus in many countries, but not in Argentina. CRISPR systems incorporate short fragments of exogenous DNA (called spacers), for example from a phage, rendering the bacterial cell and its offspring immune to future infections by either that phage or another one sharing that specific short DNA sequence. Four different CRISPR systems (CRISPR1, CRISPR2, CRISPR3 and CRISPR4) have been reported in S. thermophilus, but only CRISPR1 and CRISPR3 were found to be active against phages. In the present study, we used PCR with universal primers and determined the presence of CRISPR1 and CRISPR3 systems in 35 and 40 strains (respectively), out of 79 S. thermophilus strains tested. Among these strains, 21 presented both systems. Thirteen CRISPR1 loci were sequenced, containing 77 unique spacers, 48 found in reported phage genomes, and 1 in plasmids. Regarding CRISPR3, 28 sequenced loci contained 183 unique spacers, 123 found in phage genomes, and 7 in plasmids. Among all the spacers, 36 were "new", meaning that they were not found in databases: 6 for CRISPR1, found in a single local strain, and 30 for CRISPR3, distributed in 19 strains. The analysis of spacers showed a high similarity between our strains and those reported in other countries. However, in the local strains, a significantly lower acquisition of new and different spacers was observed in the CRISPR1 systems, which would indicate a low activity or, alternatively, a bacterial resistance to infection by most of the phages in their environment. Unlike previous reports, we found a higher proportion of unique arrangements for CRISPR3 with respect to CRISPR1, possibly indicating a greater activity of CRISPR3 systems in nationally circulating strains, although the spacer arrangements resemble those already reported in S. thermophilus. The presence of spacers in a pool of 66 bacteriophage genomes reported in the database was analyzed; CRISPR1-sp22 and CRISPR3-sp30 were the two most conserved spacers, being found in 12 and 19 phages of the pool, respectively. Our results demonstrated the diversity of CRISPR systems in S. thermophilus strains circulating in Argentina and constitute a good resource for the design of strategies to reduce the impact of bacteriophages in the regional dairy industry. Palavras-chave: Bacteriophages, CRISPR, Dairy products, Fermentations, Streptococcus thermophilus Agência de fomento:Agencia Nacional de Promoción Científica y Tecnológica (ANPCyT), Agencia Santafesina de Ciencia Tecnología e Innovación (ASaCTeI) | |||||