Proteomic Analysis of Lactobacillus species

The gut microbiota is important to human health as it provides pathogen protection and strengthens immunity. Probiotics are live microorganisms that confer positive effects on the human host, including strengthening the intestinal barrier and modulating immune response. Lactobacillus species are used in probiotic formulations and despite their relatively low abundance in the distal human gut, they are often positively or negatively correlated with intestinal diseases and infections. Lactobacilli are impacted by changes in dietary metals, like iron and zinc. Iron deficiency can promote Lactobacilli growth, zinc deficiency correlates to damaged immune systems, and zinc overload correlates with increased susceptibility to infections. Lactobacilli have low iron and high manganese needs for growth. However, the roles of these metals in metabolism and function of Lactobacilli in the gut microbiota are unclear. This study is a computational proteomic analysis aiming to identify roles of metals in Lactobacilli by analyzing metal-associated proteins. We quantified and categorized metal-associated proteins in several intestinal Lactobacillus species based on annotated proteomes pooled from the UniProtKB database. Results show at least 15% of Lactobacilli proteins are metal-associated, with zinc, manganese, and iron most abundant. Metalloproteomes of Lactobacilli are more extensive and diverse than currently recognized. Compared to well-studied bacteria like E. coli K-12, there are less proteins annotated on UniProtKB for Lactobacilli. According to our results, an average of 20.4% of proteins in the Lactobacillus bacteria are uncharacterized. Defining and characterizing the metalloproteomes of probiotics inform us which metals play important roles in their ability to colonize the host.