Pettersen, V. K. | bioRxiv Science

bioRxiv2020

Metaproteomic Profiling of Fungal Gut Colonization in Gnotobiotic Mice

Eukaryotic microbes can modulate mammalian host health and disease states, yet the molecular contribution of gut fungi remains nascent. We previously showed that mice exclusively colonized with fungi displayed increased sensitivity to allergic airway inflammation and fecal metabolite profiles similar to germ-free mice. To gain insights into the functional changes attributed to fungal colonization, we performed quantitative proteomic analyses of feces and small intestine of four-week-old gnotobiotic mice colonized with bacteria, fungi, or both. A comparison of fecal metaproteomic profiles between the mouse groups yielded broad changes in the relative levels of bacterial (46% of 2,860) and mouse (76% from 405) proteins. Many of the detected fungal proteins (3% of 1,492) have been previously reported as part of extracellular vesicles and having immunomodulating properties. Changes in the levels of mouse proteins derived from the jejunum (4% of 1,514) were mainly driven by proteins functional in lipid metabolism and apoptosis. Using metaproteomic profiling of gnotobiotic conditions, we show that fungal colonization profoundly impacts the host gut proteome. Our results suggest that an increased abundance of certain gut fungal species in early life may impact the developing intracellular balance of epithelial and immune cells.

microbiology↗

bioRxiv2020

Protein interactions between the oral bacteria Fusobacterium nucleatum and Porphyromonas gingivalis in biofilm and planktonic culture

The opportunistic pathogens Fusobacterium nucleatum and Porphyromonas gingivalis are Gram-negative bacteria associated with oral biofilm and periodontal disease. Although liquid cultures are often the preferred cultivation method in microbiology, bacterial cells in biofilm adopt a profoundly different phenotype reflecting the close cell-to-cell contact compare to their planktonic counterparts. To investigate F. nucleatum and P. gingivalis interactions relevant in biofilm formation, we applied liquid chromatography-tandem mass spectrometry to determine the expressed proteome of F. nucleatum and P. gingivalis cells that were grown either as biofilm or in planktonic culture, and individually or together. The proteomic analyses detected 1,322 F. nucleatum and 966 P. gingivalis proteins. We statistically compared the proteins label-free quantitative (LFQ) intensities between biofilm and planktonic culture and identified significant changes (p-value [≤]0.05) in 0,4% F. nucleatum proteins, 7% P. gingivalis proteins, and more than 14% of all proteins in the dual-species model. For both species, proteins involved in vitamin B2 (riboflavin) metabolic process had significantly increased levels in the biofilm condition. In both mono- and dual-species biofilm models, P. gingivalis increased the production of proteins functional in translation, oxidation-reduction, and amino acid metabolism, when compared to planktonic cultures. However, when we compared LFQ intensities between mono- and dual-species models, over 90% of the significantly changed P. gingivalis proteins had their levels reduced in biofilm and planktonic settings of the dual-species model. Our findings suggest that the two bacteria interact with each other at the protein level and indicate that P. gingivalis reduces the production of multiple proteins because of more favourable growth conditions provided by F. nucleatum presence. The results highlight the complex interactions of bacteria contributing to oral biofilm, which need to be considered in the design of future prevention strategies.

microbiology↗