Identification of Small Regulatory RNA Transcripts in Extracellular Vesicles from Lactic Acid Bacteria

Extracellular Vesicles, also referred to as EVs, are spherical lipid membrane-bound vesicles produced by both Gram positive and Gram negative bacteria. These vesicles are secreted into the extracellular space and play important roles in cellular and host communication, elimination of competitors, virulence, detoxification of environmental stress, and nutrient sensing. They are often packed with proteins, enzymes, lipids, nucleic acids and other biomolecules. Streptococcus thermophilus is a lactic acid bacteria (LAB), inhabiting the human digestive tract, that has been shown to produce EVs. The bacterial florae are known to influence the host immune system, metabolism, and neurological processes, but little is known about the biochemical pathways involved. Since EVs are involved in host communication, they may play a key role in affecting the biochemical processes of the host. To study the content and potential effects of EVs, we have grown different LAB strains under anaerobic conditions, including S. thermophilus, Lactobacillus acidophilus, and Lactobacillus bulgaricus. Our goal is to isolate EVs from these LAB strains and identify small regulatory RNA (sRNA) molecules that mediate communication and biochemical effects on the host systems. As part of this study, we have begun to identify sRNA genes in LAB strains that may mediate communication with other bacteria or the host. In S. thermophilus, we have focused on the AsdS sRNA transcript, that is 152 base pairs in length, and is involved in quorum sensing. This gene is conserved among other streptococcal species and in the human pathogen, S. pyogenes, a homologous sRNA, known as MarS, is associated with the regulation of virulence factors. Since S. thermophilus is a non-pathogenic species, the AsdS gene cannot be involved in virulence, but based on functional bioinformatics predictions, it may be responsible for intraspecies communication, biofilm formation, and transport processes. Our current studies aim to identify additional sRNA transcripts that may be found in EVs and mediate effects on the host systems.