Evaluating single-particle tracking by photo-activation localization microscopy (sptPALM) in Lactococcus lactis

Lactic acid bacteria play a central role in food fermentation, influencing both flavor and nutritional content. Despite their importance, the biochemical and microbiological mechanisms behind their behavior remain poorly understood. Single-molecule techniques offer a powerful way to study cellular processes at high resolution. However, these methods are not widely used in lactic acid bacteria due to a lack of suitable protocols and assays. Researchers have yet to test whether fluorescent proteins compatible with single-particle tracking can be used in these organisms. This gap motivated the need to explore the feasibility of using sptPALM in Lactococcus lactis. Prior work has demonstrated the utility of fluorescent proteins in other bacterial systems, but their application in LABs remains unproven. The ability to track individual proteins in real time could provide insights into gene regulation and cell-to-cell variability. No prior studies have tested photoactivatable fluorescent proteins in L. lactis for this purpose. This uncertainty drove the current investigation into fluorescent protein compatibility and tracking potential.

The goal of this research was to assess whether sptPALM can be applied to Lactococcus lactis. The study aimed to determine if fluorescent proteins suitable for single-particle tracking are functional in this organism. Researchers focused on testing various fluorescent protein variants, particularly those that are photoactivatable. The experiment sought to evaluate whether these proteins could be used to track individual dCas9 proteins in live cells. The researchers also wanted to confirm that dCas9 fused to fluorescent proteins retained its biological activity. A key objective was to observe the diffusional behavior of dCas9 in the absence of target DNA. The study aimed to establish a foundation for future investigations into CRISPR-Cas systems in LABs. This work could help develop new tools for studying gene regulation and cell function in lactic acid bacteria.

The researchers used Lactococcus lactis as the model organism for this study. They tested multiple fluorescent protein variants, including PAmCherry2, for compatibility with sptPALM. The selected proteins were fused to dCas9 to create chimeric constructs. These chimeras were introduced into L. lactis using genetic transformation techniques. The team used guide RNAs to direct dCas9 to specific genomic locations. Fluorescently labeled dCas9 was observed using sptPALM to track individual molecules. The movement of dCas9 was analyzed to identify distinct diffusional states. The researchers confirmed that the chimeras retained their gene silencing function in vivo.

The study found that PAmCherry2 was compatible with sptPALM in L. lactis. Fluorescently labeled dCas9 could be tracked as individual molecules within the cell. The dCas9 chimeras retained their ability to silence genes when bound to guide RNAs. The diffusional behavior of dCas9 showed three distinct states: free diffusion, DNA binding, and transient interaction. These states were identified through analysis of movement patterns and localization. The researchers observed that dCas9 without target DNA exhibited more random movement. The results suggest that sptPALM can be used to study CRISPR-Cas dynamics in LABs. This approach opens new possibilities for investigating gene regulation in lactic acid bacteria.

The findings indicate that sptPALM is a viable technique for studying Lactococcus lactis. The use of PAmCherry2-fused dCas9 enabled successful single-particle tracking. The dCas9 chimeras retained their gene silencing activity in the presence of guide RNAs. The observed diffusional states suggest that dCas9 interacts with DNA in multiple ways. These results support the potential of sptPALM for studying CRISPR-Cas systems in LABs. The study provides a foundation for future investigations into gene regulation and cell function. The compatibility of fluorescent proteins with L. lactis opens new experimental possibilities. This work may lead to a better understanding of microbial behavior in food fermentation.