Microbial metabolites, including B complex vitamins contribute to diverse aspects of human health. Folate, or vitamin B9, refers to a broad category of biomolecules that include pterin, para-aminobenzoic acid (pABA), and glutamate subunits. Folates are required for DNA synthesis and epigenetic regulation. In addition to dietary nutrients, the gut microbiota has been recognized as a source of B complex vitamins, including folate. This study evaluated the predicted folate synthesis capabilities in the genomes of human commensal microbes identified in the Human Microbiome Project and folate production by representative strains of six human intestinal bacterial phyla. Bacterial folate synthesis genes were ubiquitous across 512 gastrointestinal reference genomes with 13% of the genomes containing all genes required for complete de novo folate synthesis. An additional 39% of the genomes had the genetic capacity to synthesize folates in the presence of pABA, an upstream intermediate that can be obtained through diet or from other intestinal microbes. Bacterial folate synthesis was assessed during exponential and stationary phase growth through the evaluation of expression of select folate synthesis genes, quantification of total folate production, and analysis of folate polyglutamylation. Increased expression of key folate synthesis genes was apparent in exponential phase, and increased folate polyglutamylation occurred during late stationary phase. Of the folate producers, we focused on the commensal Lactobacillus reuteri to examine host–microbe interactions in relation to folate and examined folate receptors in the physiologically relevant human enteroid model. RNAseq data revealed segment-specific folate receptor distribution. Treatment of human colonoid monolayers with conditioned media (CM) from wild-type L. reuteri did not influence the expression of key folate transporters proton-coupled folate transporter (PCFT) or reduced folate carrier (RFC). However, CM from L. reuteri containing a site-specific inactivation of the folC gene, which prevents the bacteria from synthesizing a polyglutamate tail on folate, significantly upregulated RFC expression. No effects were observed using L. reuteri with a site inactivation of folC2, which results in no folate production. This work sheds light on the contributions of microbial folate to overall folate status and mammalian host metabolism.

Bacterial‐derived compounds from the intestinal microbiome modulate host mucosal immunity. Identification and mechanistic studies of these compounds provide insights into host–microbial mutualism. Specific Lactobacillus reuteri strains suppress production of the proinflammatory cytokine, tumor necrosis factor (TNF), and are protective in a mouse model of colitis. Human‐derived L. reuteri strain ATCC PTA 6475 suppresses intestinal inflammation and produces 5,10‐methenyltetrahydrofolic acid polyglutamates. Insertional mutagenesis identified the bifunctional dihydrofolate synthase/folylpolyglutamate synthase type 2 (folC2) gene as essential for 5,10‐methenyltetrahydrofolic acid polyglutamate biosynthesis, as well as for suppression of TNF production by activated human monocytes, and for the anti‐inflammatory effect of L. reuteri 6475 in a trinitrobenzene sulfonic acid‐induced mouse model of acute colitis. In contrast, folC encodes the enzyme responsible for folate polyglutamylation but does not impact TNF suppression by L. reuteri. Comparative transcriptomics between wild‐type and mutant L. reuteri strains revealed additional genes involved in immunomodulation, including previously identified hdc genes involved in histidine to histamine conversion. The folC2 mutant yielded diminished hdc gene cluster expression and diminished histamine production, suggesting a link between folate and histadine/histamine metabolism. The identification of genes and gene networks regulating production of bacterial‐derived immunoregulatory molecules may lead to improved anti‐inflammatory strategies for digestive diseases.

Colonization of the gut by certain probiotic Lactobacillus reuteri strains has been associated with reduced risk of inflammatory diseases and colorectal cancer. Previous studies pointed to a functional link between immunomodulation, histamine production, and folate metabolism, the central 1‐carbon pathway for the transfer of methyl groups. Using mass spectrometry and NMR spectroscopy, we analyzed folate metabolites of L. reuteri strain 6475 and discovered that the bacterium produces a 2‐carbon‐transporting folate in the form of 5, 10‐ethenyl‐tetrahydrofolyl polyglutamate. Isotopic labeling permitted us to trace the source of the 2‐carbon unit back to acetate of the culture medium. We show that the 2C folate cycle of L. reuteri is capable of transferring 2 carbon atoms to homocysteine to generate the unconventional amino acid ethionine, a known immunomodulator. When we treated monocytic THP‐1 cells with ethionine, their transcription of TNF‐α was inhibited and cell proliferation reduced. Mass spectrometry of THP‐1 histones revealed incorporation of ethionine instead of methionine into proteins, a reduction of histone‐methylation, and ethylation of histone lysine residues. Our findings suggest that the microbiome can expose the host to ethionine through a novel 2‐carbon transporting variant of the folate cycle and modify human chromatin via ethylation.—Roth, D., Chiang, A. J., Hu, W., Gugiu, G. B., Morra, C. N., Versalovic, J., Kalkum, M. The two‐carbon folate cycle of commensal Lactobacillus reuteri 6475 gives rise to immunomodulatory ethionine, a source for histone ethylation. FASEB J. 33,3536‐3548 (2019). http://www.fasebj.org

Purpose of review The human body plays host to bacterial biofilms across diverse anatomical sites. The treatment of pathogenic biofilm infection is confounded by their high rate of antibiotic resistance. Therefore, it is critical to understand the interplay between these biofilms and the host immune system to develop new tactics to combat these infections. Recent findings Bacterial biofilms and the components they produce affect and are affected by the host immune system. Host anatomical sites represent distinct niches in which defined bacterial biofilms are able to form and interact with the host immune system. For persistent colonization to occur, the bacteria must either avoid or suppress the host immune system, or induce an immune response that facilitates their perpetuation. Summary Commensal bacterial biofilms form a protective barrier against colonization by pathogens. Using similar mechanisms, bacteria modulate the immune system to orchestrate persistence and sometimes disease. Clinicians must balance the need to avoid disturbing beneficial commensal biofilms with the difficulty in preventing or treating pathogenic bacterial biofilms such as those that develop on medical implants and open wounds.

Gut pathogens initially encounter the host at the gastrointestinal (GI) mucus layer making its regulation a crucial aspect of gut health. Few studies have addressed bacteria‐mucus adherence or mucus oligosaccharide utilization by commensal or pathogenic bacteria. To address this gap in knowledge, the interaction between mucus (human stool, HT‐29‐MTX cells and human ileal enteroids) and commensal bacteria (B. thetaiotaomicron, C. coccoides, C. butryicum, B. producta, A. muciniphila, F. prausnitzii, R. torques, L. reuteri) or the pathogen C. difficile was examined. In vitro cultures in tryptone‐yeast extract media revealed that C. difficile and B. producta were capable of using multiple types of oligosaccharides (fucose, mannose, galactose, GlcNAc, GalNAC, sialic acid) as a sole carbon source, while other commensal bacteria exhibited specific oligosaccharide preferences. Commensal bacteria had enhanced adherence to mucus from human stool compared to HT‐29‐MTX mucus. Additionally, FITC‐labeled oligosaccharide specific lectins demonstrated that all tested commensal bacteria were capable of altering mucus oligosaccharide composition. Select commensal species were also able to stimulate mucus secretion. In contrast, the pathogen C. difficile adhered to multiple oligosaccharides in human stool mucus, but had limited adherence to HT‐29‐MTX mucus. C. difficile did not stimulate mucus secretion in HT‐29‐MTX cells and decreased secretion in enteroids. Together this data demonstrates that commensal and pathogenic bacteria adhere directly to GI mucus, but this interaction is mucin type and composition dependent. Manipulation or adherence to intestinal mucus may represent a method of bacterial‐host modulation. T32DK07644

The COVID-19 pandemic has affected all spheres of life, including the world of education. Within no time, the once-bustling university classrooms were compelled to be moved online, leaving the educators to rely on virtual engagement tools.

As evidence mounted that existing prevention methods would be insufficient to end the COVID-19 pandemic, it became clear that vaccines would be critical to achieve and maintain reduced rates of infection. However, vaccine-hesitant sentiments have become widespread, particularly in populations with lower scientific literacy. The non-STEM major (called non-major) college students represent one such population who rely on one or more science classes to develop their scientific literacy and thus, become candidates of interest for the success of the COVID-19 vaccine campaign. As these students have fewer opportunities to learn how to identify reputable scientific sources or judge the validity of novel scientific findings, it is particularly important that these skills are included in the science courses offered to non-majors. Two concurrent non-major biology courses (N = 98) at the University of Alabama at Birmingham in Spring 2021 completed Likert questionnaires with open-ended questions prior to and after an expert-led Vaccine Awareness educational intervention addressing vaccine-related concerns. In the module, experts gave presentations about COVID-19 related to microbiology, epidemiological factors, and professional experiences relating to COVID-19. Ten students agreed to participate in post-semester one-on-one interviews. Student interviews revealed that students perceived guest lecturers as providing more information and assurance. Questionnaire data showed an increase in student willingness to accept a COVID-19 vaccine as well as increased student perception of the COVID-19 vaccines as both safe and effective (Wilcoxon Rank Sum Test, p < 0.05). However, the questionnaire data revealed 10 of 98 students remained vaccine-resistant, and these students expressed insufficient research and side effects as leading vaccination concerns. Overall, we show expert-led modules can be effective in increasing non-majors willingness to accept COVID-19 vaccines. Future research should explore the experiences of non-majors and guest lectures, particularly as they relate to vaccination and vaccine concerns.

Student instructional assistants (IAs) are an integral part of most students’ college experience in higher education. When properly trained, IAs can improve students’ grades, engagement with course content, persistence, and retention.