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Commercially produced cyanobacteria preparations sold under the name spirulina are widely consumed, due to their traditional use as a nutrient-rich foodstuff and subsequent marketing as a superfood. Despite their popularity, the microbial composition of ponds used to cultivate these bacteria is understudied. A total of 19 pond samples were obtained from small-scale spirulina farms and subjected to metagenome and/or virome sequencing, and the results were analysed. A remarkable level of prokaryotic and viral diversity was found to be present in the ponds, with Limnospira sp. and Arthrospira sp. sometimes being notably scarce. A detailed breakdown of prokaryotic and viral components of 15 samples is presented. Twenty putative Limnospira sp.-infecting bacteriophage contigs were identified, though no correlation between the performance of these cultures and the presence of phages was found. The high diversity of these samples prevented the identification of clear trends in sample performance over time, between ponds or when comparing successful and failed fermentations. [ABSTRACT FROM AUTHOR]

The distinct conjugation machineries encoded by plasmids pNP40 and pUC11B represent the most prevalent plasmid transfer systems among lactococcal strains. In the current study, we identified genetic determinants that underpin pNP40‐ and pUC11B‐mediated, high‐frequency mobilisation of other, non‐conjugative plasmids. The mobilisation frequencies of the smaller, non‐conjugative plasmids and the minimal sequences required for their mobilisation were determined, owing to the determination of the oriT sequences of both pNP40 and pUC11B, which allowed the identification of similar sequences in some of the non‐conjugative plasmids that were shown to promote their mobilisation. Furthermore, the auxiliary gene mobC, two distinct functional homologues of which are present in several plasmids harboured by the pNP40‐ and pUC11B‐carrying host strains, was observed to confer a high‐frequency mobilisation phenotype. These findings provide mechanistic insights into how lactococcal conjugative plasmids achieve conjugation and promote mobilisation of non‐conjugative plasmids. Ultimately, these insights would be harnessed to optimise conjugation and mobilisation strategies for the rapid and predictable development of robust and technologically improved strains. [ABSTRACT FROM AUTHOR]

Bacteriophages (or phages) represent a persistent threat to the success and reliability of food fermentation processes. Recent reports of phages that infect Streptococcus thermophilus have highlighted the diversification of phages of this species. Phages of S. thermophilus typically exhibit a narrow range, a feature that is suggestive of diverse receptor moieties being presented on the cell surface of the host. Cell wall polysaccharides, including rhamnose-glucose polysaccharides and exopolysaccharides have been implicated as being involved in the initial interactions with several phages of this species. Following internalization of the phage genome, the host presents several defences, including CRISPR-Cas and restriction and modification systems to limit phage proliferation. This review provides a current and holistic view of the interactions of phages and their S. thermophilus host cells and how this has influenced the diversity and evolution of both entities. [ABSTRACT FROM AUTHOR]

Pecorino Siciliano PDO is a semi-hard cheese that is produced in wooden vats using raw sheep's milk and its associated autochthonous microbial community. In the present study, we evaluated the microbial ecology of the milk, curd and whey from five Pecorino Siciliano PDO-producing farms in Sicily using a combination of metagenomic and microbiological approaches. We present an overview of the species and strain-level diversity of dairy lactococcal and streptococcal isolates using established genotyping tools and compare the lactic acid bacterial populations present in samples from these farms. Whole genome sequences of representative isolates of Lactococcus spp. and Streptococcus thermophilus were elucidated and the genetic diversity of the strains was established through analysis of predicted phage-resistance systems and prophage-associated regions. The analysis revealed farm-specific dairy lactococcal and streptococcal isolates that possess diverse genotypic features including newly described phage-resistance systems. [ABSTRACT FROM AUTHOR]