Crossing Kingdoms: How the Mycobiota and Fungal-Bacterial Interactions Impact Host Health and Disease

The pathobiology of human fungal infections

Human fungal infections are a historically neglected area of disease research, yet they cause more than 1.5 million deaths every year. Our understanding of the pathophysiology of these infections has increased considerably over the past decade, through major insights into both the host and pathogen factors that contribute to the phenotype and severity of these diseases. Recent studies are revealing multiple mechanisms by which fungi modify and manipulate the host, escape immune surveillance and generate complex comorbidities. Although the emergence of fungal strains that are less susceptible to antifungal drugs or that rapidly evolve drug resistance is posing new threats, greater understanding of immune mechanisms and host susceptibility factors is beginning to offer novel immunotherapeutic options for the future. In this Review, we provide a broad and comprehensive overview of the pathobiology of human fungal infections, focusing specifically on pathogens that can cause invasive life-threatening infections, highlighting recent discoveries from the pathogen, host and clinical perspectives. We conclude by discussing key future challenges including antifungal drug resistance, the emergence of new pathogens and new developments in modern medicine that are promoting susceptibility to infection.

Pyricularia oryzae enhances Streptomyces griseus growth via non-volatile alkaline metabolites

Chemical compounds that affect microbial interactions have attracted wide interest. In this study, Streptomyces griseus showed enhanced growth when cocultured with the rice blast fungus Pyricularia oryzae on potato dextrose agar (PDA) medium. An improvement in S. griseus growth was observed before contact with P. oryzae, and no growth-promoting effect was observed when the growth medium between the two microorganisms was separated. These results suggested that the chemicals produced by P. oryzae diffused through the medium and were not volatile. A PDA plate supplemented with phenol red showed that the pH of the area surrounding P. oryzae increased. The area with increased pH promoted S. griseus growth, suggesting that the alkaline compounds produced by P. oryzae were involved in this growth stimulation. In contrast, coculture with the soilborne plant pathogen Fusarium oxysporum and entomopathogenic fungus Cordyceps tenuipes did not promote S. griseus growth. Furthermore, DL-α-Difluoromethylornithine, a polyamine biosynthesis inhibitor, prevented the increase in pH and growth promotion of S. griseus by P. oryzae. These results indicated that P. oryzae increased pH by producing a polyamine.

Controlling Candida: immune regulation of commensal fungi in the gut

The intestinal microbiome harbors fungi that pose a significant risk to human health as opportunistic pathogens and drivers of inflammation. Inflammatory and autoimmune diseases are associated with dysbiotic fungal communities and the expansion of potentially pathogenic fungi. The gut is also the main reservoir for disseminated fungal infections. Immune interactions are critical for preventing commensal fungi from becoming pathogenic. Significant strides have been made in defining innate and adaptive immune pathways that regulate intestinal fungi, and these discoveries have coincided with advancements in our understanding of the fungal molecular pathways and effectors involved in both commensal colonization and pathogenesis within the gut. In this review, we will discuss immune interactions important for regulating commensal fungi, with a focus on how specific cell types and effectors interact with fungi to limit their colonization or pathogenic potential. This will include how innate and adaptive immune pathways target fungi and orchestrate antifungal immune responses, in addition to how secreted immune effectors, such as mucus and antimicrobial peptides, regulate fungal colonization and inhibit pathogenic potential. These immune interactions will be framed around our current understanding of the fungal effectors and pathways regulating colonization and pathogenesis within this niche. Finally, we highlight important unexplored mechanisms by which the immune system regulates commensal fungi in the gut.

Navigating the fungal battlefield: cysteine-rich antifungal proteins and peptides from Eurotiales

Fungi are ubiquitous in the environment and play a key role in the decomposition and recycling of nutrients. On the one hand, their special properties are a great asset for the agricultural and industrial sector, as they are used as source of nutrients, producers of enzymes, pigments, flavorings, and biocontrol agents, and in food processing, bio-remediation and plant growth promotion. On the other hand, they pose a serious challenge to our lives and the environment, as they are responsible for fungal infections in plants, animals and humans. Although host immunity opposes invading pathogens, certain factors favor the manifestation of fungal diseases. The prevalence of fungal infections is on the rise, and there is an alarming increase in the resistance of fungal pathogens to approved drugs. The limited number of antimycotics, the obstacles encountered in the development of new drugs due to the poor tolerability of antifungal agents in patients, the limited number of unique antifungal targets, and the low species specificity contribute to the gradual depletion of the antifungal pipeline and newly discovered antifungal drugs are rare. Promising candidates as next-generation therapeutics are antimicrobial proteins and peptides (AMPs) produced by numerous prokaryotic and eukaryotic organisms belonging to all kingdom classes. Importantly, filamentous fungi from the order Eurotiales have been shown to be a rich source of AMPs with specific antifungal activity. A growing number of published studies reflects the efforts made in the search for new antifungal proteins and peptides (AFPs), their efficacy, species specificity and applicability. In this review, we discuss important aspects related to fungi, their impact on our life and issues involved in treating fungal infections in plants, animals and humans. We specifically highlight the potential of AFPs from Eurotiales as promising alternative antifungal therapeutics. This article provides insight into the structural features, mode of action, and progress made toward their potential application in a clinical and agricultural setting. It also identifies the challenges that must be overcome in order to develop AFPs into therapeutics.

The signatures and crosstalk of gut microbiome, mycobiome, and metabolites in decompensated cirrhotic patients

Background

Numerous studies have confirmed that gut microbiota plays a crucial role in the progression of cirrhosis. However, the contribution of gut fungi in cirrhosis is often overlooked due to the relatively low abundance.

Methods

We employed 16S ribosomal RNA sequencing, internal transcribed spacer sequencing, and untargeted metabolomics techniques to investigate the composition and interaction of gut bacteria, fungi, and metabolites in cirrhotic patients.

Results

Cirrhotic patients exhibited significant differences in the diversity and composition of gut microbiota and their metabolites in cirrhotic patients compared to healthy individuals. Increase in pathogenic microbial genera and a decrease in beneficial microbial genera including bacteria and fungi were observed. Various clinical indexes were closely connected with these increased metabolites, bacteria, fungi. Additionally, endoscopic treatment was found to impact the gut microbiota and metabolites in cirrhotic patients, although it did not significantly alter the gut ecology. Finally, we constructed a cirrhosis diagnostic model based on different features (bacteria, fungi, metabolites, clinical indexes) with an AUC of 0.938.

Conclusion

Our findings revealed the characteristics of gut microbial composition and their intricate internal crosstalk in cirrhotic patients, providing cutting-edge explorations of potential roles of gut microbes in cirrhosis.

Commensal Yeast Promotes Salmonella Typhimurium Virulence

Enteric pathogens engage in complex interactions with the host and the resident microbiota to establish gut colonization. Although mechanistic interactions between enteric pathogens and bacterial commensals have been extensively studied, whether and how commensal fungi affect pathogenesis of enteric infections remains largely unknown. Here we show that colonization with the common human gut commensal fungus Candida albicans worsened infections with the enteric pathogen Salmonella enterica serovar Typhimurium. Presence of C. albicans in the mouse gut increased Salmonella cecum colonization and systemic dissemination. We investigated the underlying mechanism and found that Salmonella binds to C. albicans via Type 1 fimbriae and uses its Type 3 Secretion System (T3SS) to deliver effector proteins into C. albicans . A specific effector, SopB, was sufficient to manipulate C. albicans metabolism, triggering increased arginine biosynthesis in C. albicans and the release of millimolar amounts of arginine into the extracellular environment. The released arginine, in turn, induced T3SS expression in Salmonella , increasing its invasion of epithelial cells. C. albicans deficient in arginine production was unable to increase Salmonella virulence in vitro or in vivo . In addition to modulating pathogen invasion, arginine also directly influenced the host response to infection. Arginine-producing C. albicans dampened the inflammatory response during Salmonella infection, whereas C. albicans deficient in arginine production did not. Arginine supplementation in the absence of C. albicans increased the systemic spread of Salmonella and decreased the inflammatory response, phenocopying the presence of C. albicans . In summary, we identified C. albicans colonization as a susceptibility factor for disseminated Salmonella infection, and arginine as a central metabolite in the cross-kingdom interaction between fungi, bacteria, and host.

Cross interaction between bacterial and fungal microbiota and their relevance to human health and disease: mechanistic pathways and prospective therapy

Diverse bacterial and fungal microbiota communities inhabit the human body, and their presence is essential for maintaining host homeostasis. The oral cavity, lung, gut, and vagina are just a few of the bodily cavities where these microorganisms communicate with one another, either directly or indirectly. The effects of this interaction can be either useful or detrimental to the host. When the healthy microbial diversity is disturbed, for instance, as a result of prolonged treatment with broad spectrum antibiotics, this allows the growth of specific microbes at the expense of others and alters their pathogenicity, causing a switch of commensal germs into pathogenic germs, which could promote tissue invasion and damage, as occurs in immunocompromised patients. Consequently, antimicrobials that specifically target pathogens may help in minimizing secondary issues that result from the disruption of useful bacterial/fungal interactions (BFIs). The interface between Candida albicans and Aspergillus fumigatus with bacteria at various body sites is emphasized in the majority of the medically important BFIs that have been reported thus far. This interface either supports or inhibits growth, or it enhances or blocks the generation of virulence factors. The aim of this review is to draw attention to the link between the bacterial and fungal microbiota and how they contribute to both normal homeostasis and disease development. Additionally, recent research that has studied microbiota as novel antimicrobials is summarized.

Unveiling the mycobiota: The fungal frontier of human health

The microbiota and its effect on health has been extensively studied over the past decade. In many studies, the term microbiota has become synonymous with the bacterial component of the microbiota. Other microbes in the microbiota, such as viruses and fungi, have been neglected until recently. This special issue provides some background on the mycobiota and explores the role of gut fungi in human diseases such as cancer, metabolic diseases, and infection by Clostridiodes difficile, and describes the incidence of fungal infections in transplant patients. The mycobiota, once overlooked, now garners increasing attention.

Hand contamination and hand hygiene knowledge and practices among commercial transport users after the SARS-CoV-2 virus (COVID-19) scare, Enugu State, Nigeria

Contaminated hands are one of the most common modes of microorganism transmission that are responsible for many associated infections in healthcare, food industries, and public places such as transportation parks. Public health approaches during COVID-19 pandemic have shown that hand hygiene practices and associated knowledge are critical measure to control the spread of infectious agent. Hence, assessment of commercial transport users' knowledge, belief and practices on hand hygiene, and potential contamination with infectious agents which is the aim of the study, aligns with general health concern of quantifying contamination risk levels to predict disease outbreaks. This study utilized a randomized sampling approach to select 10 frequently used commercial parks within two districts in the State: Enugu and Nsukka. The parameters analysed include a cross-sectional questionnaire survey, hand swab and hand washed samples collected from dominant hand of participants. A total of 600 participants responded to the questionnaire survey, while 100 participants' hand swabs were examined for microbial contamination. This study recorded a high prevalence of fungal (90.0%) and bacterial (87.0%) species; 20 species of fungus were identified with prevalence range of 1% to 14%; 21 bacterial species were isolated with prevalence range of 1% to 16%. These species were identified as either opportunistic, non-invasive, or pathogenic, which may constitute a health concern amongst immunocompromised individuals within the population. Aspergillus spp. (14%), was the most common fungal species that was exclusively found amongst Nsukka commercial users, while E. coli was the most prevalent isolated bacterial species amongst Nsukka (12%) and Enugu (20%) commercial park users. Prevalence of fungal contamination in Nsukka (94.0%; 47/50) and Enugu (86.0%; 43/50) were both high. Prevalence of bacterial contamination was higher in Enugu than Nsukka but not significantly (47[94.0%] vs. 40[80.0%], p = 0.583). A greater number of participants (99.3%) were aware of the importance of hand hygiene, however with low compliance rate aside "after using the toilet" (80%) and "before eating" (90%), other relevant hand washing and sanitizing practices were considered less important. With these observations, we can emphatically say that despite the COVID-19 scare, commercial park users within the sampled population do not efficiently practice quality hand wash and hygiene measures, hence, risking the widespread of infectious agents in situation of disease outbreak or among immunocompromised individuals.

IL-22-dependent responses and their role during Citrobacter rodentium infection

The mouse pathogen Citrobacter rodentium is utilized as a model organism for studying infections caused by the human pathogens enteropathogenic Escherichia coli (EPEC) and enterohemorrhagic E. coli (EHEC) and to elucidate mechanisms of mucosal immunity. In response to C. rodentium infection, innate lymphoid cells and T cells secrete interleukin (IL)-22, a cytokine that promotes mucosal barrier function. IL-22 plays a pivotal role in enabling mice to survive and recover from C. rodentium infection, although the exact mechanisms involved remain incompletely understood. Here, we investigated whether particular components of the host response downstream of IL-22 contribute to the cytokine's protective effects during C. rodentium infection. In line with previous research, mice lacking the IL-22 gene (Il22-/- mice) were highly susceptible to C. rodentium infection. To elucidate the role of specific antimicrobial proteins modulated by IL-22, we infected the following knockout mice: S100A9-/- (calprotectin), Lcn2-/- (lipocalin-2), Reg3b-/- (Reg3β), Reg3g-/- (Reg3γ), and C3-/- (C3). All knockout mice tested displayed a considerable level of resistance to C. rodentium infection, and none phenocopied the lethality observed in Il22-/- mice. By investigating another arm of the IL-22 response, we observed that C. rodentium-infected Il22-/- mice exhibited an overall decrease in gene expression related to intestinal barrier integrity as well as significantly elevated colonic inflammation, gut permeability, and pathogen levels in the spleen. Taken together, these results indicate that host resistance to lethal C. rodentium infection may depend on multiple antimicrobial responses acting in concert, or that other IL-22-regulated processes, such as tissue repair and maintenance of epithelial integrity, play crucial roles in host defense to attaching and effacing pathogens.

Alterations in the gut mycobiome with coronary artery disease severity

BACKGROUND

Coronary artery disease (CAD) is a prevalent cardiovascular condition, and numerous studies have linked gut bacterial imbalance to CAD. However, the relationship of gut fungi, another essential component of the intestinal microbiota, with CAD remains poorly understood.

METHODS

In this cross-sectional study, we analyzed fecal samples from 132 participants, split into 31 healthy controls and 101 CAD patients, further categorized into stable CAD (38), unstable angina (41), and acute myocardial infarction (22) groups. We conducted internal transcribed spacer 1 (ITS1) and 16S sequencing to examine gut fungal and bacterial communities.

FINDINGS

Based on ITS1 analyses, Ascomycota and Basidiomycota were the dominant fungal phyla in all the groups. The α diversity of gut mycobiome remained unaltered among the control group and CAD subgroups; however, the structure and composition of the mycobiota differed significantly with the progression of CAD. The abundances of 15 taxa gradually changed with the occurrence and progression of the disease and were significantly correlated with major CAD risk factor indicators. The mycobiome changes were closely linked to gut microbiome dysbiosis in patients with CAD. Furthermore, disease classifiers based on gut fungi effectively identified subgroups with different degrees of CAD. Finally, the FUNGuild analysis further categorized these fungi into distinct ecological guilds.

INTERPRETATION

In conclusion, the structure and composition of the gut fungal community differed from healthy controls to various subtypes of CAD, revealing key fungi taxa alterations linked to the onset and progression of CAD. Our study highlights the potential role of gut fungi in CAD and may facilitate the development of novel biomarkers and therapeutic targets for CAD.

FUNDING

This work was supported by the grants from the National Natural Science Foundation of China (No. 82170302, 92168117, 82370432), National clinical key specialty construction project- Cardiovascular Surgery, the Reform and Development Program of Beijing Institute of Respiratory Medicine (No. Ggyfz202417, Ggyfz202308), the Beijing Natural Science Foundation (No. 7222068); and the Clinical Research Incubation Program of Beijing Chaoyang Hospital Affiliated to Capital Medical University (No. CYFH202209).

The yeast-human coevolution: Fungal transition from passengers, colonizers, and invaders

Fungi are the cause of more than a billion infections in humans every year, although their interactions with the host are still neglected compared to bacteria. Major systemic fungal infections are very unusual in the healthy population, due to the long history of coevolution with the human host. Humans are routinely exposed to environmental fungi and can host a commensal mycobiota, which is increasingly considered as a key player in health and disease. Here, we review the current knowledge on host-fungi coevolution and the factors that regulate their interaction. On one hand, fungi have learned to survive and inhabit the host organisms as a natural ecosystem, on the other hand, the host immune system finely tunes the response toward fungi. In turn, recognition of fungi as commensals or pathogens regulates the host immune balance in health and disease. In the human gut ecosystem, yeasts provide a fingerprint of the transient microbiota. Their status as passengers or colonizers is related to the integrity of the gut barrier and the risk of multiple disorders. Thus, the study of this less known component of the microbiota could unravel the rules of the transition from passengers to colonizers and invaders, as well as their dependence on the innate component of the host's immune response. This article is categorized under: Infectious Diseases > Environmental Factors Immune System Diseases > Environmental Factors Infectious Diseases > Molecular and Cellular Physiology.

Gut bacterial and fungal dysbiosis in tuberculosis patients

BACKGROUND

Recent studies have more focused on gut microbial alteration in tuberculosis (TB) patients. However, no detailed study on gut fungi modification has been reported till now. So, current research explores the characteristics of gut microbiota (bacteria)- and mycobiota (fungi)-dysbiosis in TB patients and also assesses the correlation between the gut microbiome and serum cytokines. It may help to screen the potential diagnostic biomarker for TB.

RESULTS

The results show that the alpha diversity of the gut microbiome (including bacteria and fungi) decreased and altered the gut microbiome composition of TB patients. The bacterial genera Bacteroides and Prevotella were significantly increased, and Blautia and Bifidobacterium decreased in the TB patients group. The fungi genus Saccharomyces was increased while decreased levels of Aspergillus in TB patients. It indicates that gut microbial equilibrium between bacteria and fungi has been altered in TB patients. The fungal-to-bacterial species ratio was significantly decreased, and the bacterial-fungal trans-kingdom interactions have been reduced in TB patients. A set model including Bacteroides, Blautia, Eubacterium_hallii_group, Apiotrichum, Penicillium, and Saccharomyces may provide a better TB diagnostics option than using single bacterial or fungi sets. Also, gut microbial dysbiosis has a strong correlation with the alteration of IL-17 and IFN-γ.

CONCLUSIONS

Our results demonstrate that TB patients exhibit the gut bacterial and fungal dysbiosis. In the clinics, some gut microbes may be considered as potential biomarkers for auxiliary TB diagnosis.

A molecular view on the interference established between vaginal Lactobacilli and pathogenic Candida species: Challenges and opportunities for the development of new therapies

Vaginal infectious diseases caused by viruses and bacteria have been linked to the occurrence of dysbiosis, that is, a reduction in the abundance of the normally dominating vaginal Lactobacillus species. Mucosal infections in the vagina and/or vulva caused by Candida species, usually known as vulvovaginal candidiasis (or VVC), are among the leading causes of diseases in the vaginal tract. The existence of a clear link between the occurrence of dysbiosis and the development of VVC is still unclear, although multiple observations point in that direction. Based on the idea that vaginal health is linked to a microbiota dominated by lactobacilli, several probiotics have been used in management of VVC, either alone or in combination with antifungals, having obtained different degrees of success. In most cases, the undertaken trials resorted to lactobacilli species other than those indigenous to the vaginal tract, although in vitro these vaginal species were shown to reduce growth, viability and virulence of Candida. In this paper we overview the role of lactobacilli and Candida in the vaginal micro- and myco-biomes, while discussing the results obtained in what concerns the establishment of interference mechanisms in vivo and the environmental factors that could determine that. We also overview the molecular mechanisms by which lactobacilli species have been shown to inhibit pathophysiology of Candida, including the description of the genes and pathways determining their ability to thrive in the presence of each other. In a time where concerns are increasing with the emergence of antifungal resistance and the slow pace of discovery of new antifungals, a thorough understanding of the molecular mechanisms underneath the anti-Candida effect prompted by vaginal lactobacilli is of utmost importance to assure a knowledge-based design of what can be a new generation of pharmaceuticals, eventually focusing therapeutic targets other than the usual ones.

Fungal coexistence in the skin mycobiome: a study involving Malassezia, Candida, and Rhodotorula

Evidence of fungal coexistence in humans points towards fungal adaptation to the host environment, like the skin. The human commensal Malassezia has evolved, especially residing in sebum-rich areas of the mammalian body where it can get the necessary nutrition for its survival. This fungus is primarily responsible for skin diseases like Pityriasis versicolor (PV), characterized by hypo or hyperpigmented skin discoloration and erythematous macules. In this manuscript, we report a 19-year-old healthy female who presented with a one-year history of reddish, hypopigmented, asymptomatic lesions over the chest and a raised erythematous lesion over the face. Upon clinical observation, the patient displayed multiple erythematous macules and erythematous papules over the bilateral malar area of the face, along with multiple hypopigmented scaly macules present on the chest and back. Based on the above clinical findings, a diagnosis of PV and Acne vulgaris (AV) was made. Interestingly, the patient was immunocompetent and didn't have any comorbidities. Upon isolation of skin scrapings and post-culturing, we found the existence of three fungal genera in the same region of the patient's body. We further went on to confirm the identity of the particular species and found it to represent Malassezia, Rhodotorula, and Candida. We report how Malassezia, the predominant microbial resident skin fungus, coexists with other fungal members of the skin mycobiome. This study on an applied aspect of microbiology also shows how important it is to identify the fungal organism associated with skin infections so that appropriate therapeutics can be advised to avoid cases of relapse.

Cyberlindnera jadinii and Kluyveromyces lactis, two fungi used in food processes, have potential probiotic effects on gut inflammation

IMPORTANCE

The food industry has always used many strains of microorganisms including fungi in their production processes. These strains have been widely characterized for their biotechnological value, but we still know very little about their interaction capacities with the host at a time when the intestinal microbiota is at the center of many pathologies. In this study, we characterized five yeast strains from food production which allowed us to identify two new strains with high probiotic potential and beneficial effects in a model of intestinal inflammation.

Gut-joint axis in knee synovitis: gut fungal dysbiosis and altered fungi-bacteria correlation network identified in a community-based study

OBJECTIVES

Knee synovitis is a highly prevalent and potentially curable condition for knee pain; however, its pathogenesis remains unclear. We sought to assess the associations of the gut fungal microbiota and the fungi-bacteria correlation network with knee synovitis.

METHODS

Participants were derived from a community-based cross-sectional study. We performed an ultrasound examination of both knees. A knee was defined as having synovitis if its synovium was ≥4 mm and/or Power Doppler (PD) signal was within the knee synovium area (PD synovitis). We collected faecal specimens from each participant and assessed gut fungal and bacterial microbiota using internal transcribed spacer 2 and shotgun metagenomic sequencing. We examined the relation of α-diversity, β-diversity, the relative abundance of taxa and the interkingdom correlations to knee synovitis.

RESULTS

Among 977 participants (mean age: 63.2 years; women: 58.8%), 191 (19.5%) had knee synovitis. β-diversity of the gut fungal microbiota, but not α-diversity, was significantly associated with prevalent knee synovitis. The fungal genus Schizophyllum was inversely correlated with the prevalence and activity (ie, control, synovitis without PD signal and PD synovitis) of knee synovitis. Compared with those without synovitis, the fungi-bacteria correlation network in patients with knee synovitis was smaller (nodes: 93 vs 153; edges: 107 vs 244), and the average number of neighbours was fewer (2.3 vs 3.2).

CONCLUSION

Alterations of gut fungal microbiota and the fungi-bacteria correlation network are associated with knee synovitis. These novel findings may help understand the mechanisms of the gut-joint axis in knee synovitis and suggest potential targets for future treatment.

Candida-bacterial cross-kingdom interactions

While the fungus Candida albicans is a common colonizer of healthy humans, it is also responsible for mucosal infections and severe invasive disease. Understanding the mechanisms that allow C. albicans to exist as both a benign commensal and as an invasive pathogen have been the focus of numerous studies, and recent findings indicate an important role for cross-kingdom interactions on C. albicans biology. This review highlights how C. albicans-bacteria interactions influence healthy polymicrobial community structure, host immune responses, microbial pathogenesis, and how dysbiosis may lead to C. albicans infection. Finally, we discuss how cross-kingdom interactions represent an opportunity to identify new antivirulence compounds that target fungal infections.

Commensal fungi in intestinal health and disease

The microbiota is known to influence several facets of mammalian development, digestion and disease. Most studies of the microbiota have focused on the bacterial component, but the importance of commensal fungi in health and disease is becoming increasingly clear. Although fungi account for a smaller proportion of the microbiota than bacteria by number, they are much larger and therefore account for a substantial proportion of the biomass. Moreover, as fungi are eukaryotes, their metabolic pathways are complex and unique. In this Review, we discuss the evidence for involvement of specific members of the mycobiota in intestinal diseases, including inflammatory bowel disease, colorectal cancer and pancreatic cancer. We also highlight the importance of fungal interactions with intestinal bacteria and with the immune system. Although most studies of commensal fungi have focused on their role in disease, we also consider the beneficial effects of fungal colonies in the gut. The evidence highlights potential opportunities to target fungi and their interactions for therapeutic purposes.

Aspects of oral streptococcal metabolic diversity: Imagining the landscape beneath the fog

It is widely acknowledged that the human-associated microbial community influences host physiology, systemic health, disease progression, and even behavior. There is currently an increased interest in the oral microbiome, which occupies the entryway to much of what the human initially encounters from the environment. In addition to the dental pathology that results from a dysbiotic microbiome, microbial activity within the oral cavity exerts significant systemic effects. The composition and activity of the oral microbiome is influenced by (1) host-microbial interactions, (2) the emergence of niche-specific microbial "ecotypes," and (3) numerous microbe-microbe interactions, shaping the underlying microbial metabolic landscape. The oral streptococci are central players in the microbial activity ongoing in the oral cavity, due to their abundance and prevalence in the oral environment and the many interspecies interactions in which they participate. Streptococci are major determinants of a healthy homeostatic oral environment. The metabolic activities of oral Streptococci, particularly the metabolism involved in energy generation and regeneration of oxidative resources vary among the species and are important factors in niche-specific adaptations and intra-microbiome interactions. Here we summarize key differences among streptococcal central metabolic networks and species-specific differences in how the key glycolytic intermediates are utilized.

Feed Regime Slightly Modifies the Bacterial but Not the Fungal Communities in the Intestinal Mucosal Microbiota of Cobia Fish (Rachycentron canadum)

The bacterial community of the intestinal microbiota influences many host functions, and similar effects have been recently reported for the fungal community (mycobiota). Cobia is a tropical fish that has been studied for its potential in marine aquaculture. However, the study of its bacterial community has been underreported and the mycobiota has not been investigated. We analyzed the gut bacterial and fungal profile present in the intestinal mucosa of reared adult cobias fed two diets (frozen fish pieces (FFPs) and formulated feed (FF)) for 4 months by sequencing the 16S rRNA (V3-V4) and internal transcribed spacer-2 (ITS2) regions using Illumina NovaSeq 6000. No significant differences in the alpha diversity of the bacterial community were observed, which was dominated by the phyla Proteobacteria (~96%) and Firmicutes (~1%). Cobia fed FF showed higher abundance of 10 genera, mainly UCG-002 (Family Oscillospiraceae) and Faecalibacterium, compared to cobia fed FFPs, which showed higher abundance of 7 genera, mainly Methylobacterium-Methylorubrum and Cutibacterium. The inferred bacterial functions were related to metabolism, environmental information processing and cellular processes; and no differences were found between diets. In mycobiota, no differences were observed in the diversity and composition of cobia fed the two diets. The mycobiota was dominated by the phyla Ascomycota (~88%) and Basidiomycota (~11%). This is the first study to describe the gut bacterial and fungal communities in cobia reared under captive conditions and fed on different diets and to identify the genus Ascobulus as a new member of the core fish mycobiota.

The Intricate Connection between Bacterial α-Diversity and Fungal Engraftment in the Human Gut of Healthy and Impaired Individuals as Studied Using the In Vitro SHIME® Model

From the estimated 2.2 to 3.8 million fungal species existing on Earth, only a minor fraction actively colonizes the human gastrointestinal tract. In fact, these fungi only represent 0.1% of the gastrointestinal biosphere. Despite their low abundance, fungi play dual roles in human health-both beneficial and detrimental. Fungal infections are often associated with bacterial dysbiosis following antibiotic use, yet our understanding of gut fungi-bacteria interactions remains limited. Here, we used the SHIME® gut model to explore the colonization of human fecal-derived fungi across gastrointestinal compartments. We accounted for the high inter-individual microbial diversity by using fecal samples from healthy adults, healthy babies, and Crohn's disease patients. Using quantitative Polymerase Chain Reaction and targeted next-generation sequencing, we demonstrated that SHIME®-colonized mycobiomes change upon loss of transient colonizers. In addition, SHIME® reactors from Crohn's disease patients contained comparable bacterial levels as healthy adults but higher fungal concentrations, indicating unpredictable correlations between fungal levels and total bacterial counts. Our findings rather link higher bacterial α-diversity to limited fungal growth, tied to colonization resistance. Hence, while healthy individuals had fewer fungi engrafting the colonic reactors, low α-diversity in impaired (Crohn's disease patients) or immature (babies) microbiota was associated with greater fungal abundance. To validate, antibiotic-treated healthy colonic microbiomes demonstrated increased fungal colonization susceptibility, and bacterial taxa that were negatively correlated with fungal expansion were identified. In summary, fungal colonization varied individually and transiently, and bacterial resistance to fungal overgrowth was more related with specific bacterial genera than total bacterial load. This study sheds light on fungal-bacterial dynamics in the human gut.

Nutritional Provision of Iron Complexes by the Major Allergen Alt a 1 to Human Immune Cells Decreases Its Presentation

Alternaria alternata is a common fungus strongly related with severe allergic asthma, with 80% of affected individuals being sensitized solely to its major allergen Alt a 1. Here, we assessed the function of Alt a 1 as an innate defense protein binding to micronutrients, such as iron-quercetin complexes (FeQ2), and its impact on antigen presentation in vitro. Binding of Alt a 1 to FeQ2 was determined in docking calculations. Recombinant Alt a 1 was generated, and binding ability, as well as secondary and quaternary structure, assessed by UV-VIS, CD, and DLS spectroscopy. Proteolytic functions were determined by casein and gelatine zymography. Uptake of empty apo- or ligand-filled holoAlt a 1 were assessed in human monocytic THP1 cells under the presence of dynamin and clathrin-inhibitors, activation of the Arylhydrocarbon receptor (AhR) using the human reporter cellline AZ-AHR. Human PBMCs were stimulated and assessed for phenotypic changes in monocytes by flow cytometry. Alt a 1 bound strongly to FeQ2 as a tetramer with calculated Kd values reaching pico-molar levels and surpassing affinities to quercetin alone by a factor of 5000 for the tetramer. apoAlt a 1 but not holoAlta 1 showed low enzymatic activity against casein as a hexamer and gelatin as a trimer. Uptake of apo- and holo-Alt a 1 occurred partly clathrin-dependent, with apoAlt a 1 decreasing labile iron in THP1 cells and holoAlt a 1 facilitating quercetin-dependent AhR activation. In human PBMCs uptake of holoAlt a 1 but not apoAlt a 1 significantly decreased the surface expression of the costimulatory CD86, but also of HLADR, thereby reducing effective antigen presentation. We show here for the first time that the presence of nutritional iron complexes, such as FeQ2, significantly alters the function of Alt a 1 and dampens the human immune response, thereby supporting the notion that Alt a 1 only becomes immunogenic under nutritional deprivation.

Gut fungal mycobiome: A significant factor of tumor occurrence and development

A variety of bacteria, viruses, fungi, protists, archaea and protozoa coexists within the mammalian gastrointestinal (GI) tract such as that fungi are detectable in all intestinal and colon segments in almost all healthy adults. Although fungi can cause infectious diseases, they are also related to gut and systemic homeostasis. Importantly, through transformation of different forms such as from yeast to hyphae, interaction among gut microbiota such as fungal and bacterial interaction, host factors such as immune and host derived factors, and fungus genetic and epigenetic factors, fungi can be transformed from commensal into pathogenic lifestyles. Recent studies have shown that fungi play a significant role in the occurrence and development of tumors such as colorectal cancer. Indeed, evidences have shown that multiple species of different fungi exist in different tumors. Studies have also demonstrated that fungi are related to the occurrence and development of tumors, and also survival of patients. Here we summarize recent advances in the transformation of fungi from commensal into pathogenic lifestyles, and the effects of gut pathogenic fungi on the occurrence and development of tumors such as colorectal and pancreatic cancers.

Immune responses to human fungal pathogens and therapeutic prospects

Pathogenic fungi have emerged as significant causes of infectious morbidity and death in patients with acquired immunodeficiency conditions such as HIV/AIDS and following receipt of chemotherapy, immunosuppressive agents or targeted biologics for neoplastic or autoimmune diseases, or transplants for end organ failure. Furthermore, in recent years, the spread of multidrug-resistant Candida auris has caused life-threatening outbreaks in health-care facilities worldwide and raised serious concerns for global public health. Rapid progress in the discovery and functional characterization of inborn errors of immunity that predispose to fungal disease and the development of clinically relevant animal models have enhanced our understanding of fungal recognition and effector pathways and adaptive immune responses. In this Review, we synthesize our current understanding of the cellular and molecular determinants of mammalian antifungal immunity, focusing on observations that show promise for informing risk stratification, prognosis, prophylaxis and therapies to combat life-threatening fungal infections in vulnerable patient populations.

The bovine nasal fungal community and associations with bovine respiratory disease

Introduction

Effective identification and treatment of bovine respiratory disease (BRD) is an ongoing health and economic issue for the dairy and beef cattle industries. Bacteria pathogens Pasteurellamultocida, Mycoplasmabovis, Mannheimia haemolytica, and Histophilus somni and the virus Bovine herpesvirus-1 (BHV-1), Bovine parainfluenza-3 virus (BPIV-3), Bovine respiratory syncytial virus (BRSV), Bovine adenovirus 3 (BAdV3), bovine coronavirus (BoCV) and Bovine viral diarrhea virus (BVDV) have commonly been identified in BRD cattle; however, no studies have investigated the fungal community and how it may also relate to BRD.

Methods

The objective of this study was to understand if the nasal mycobiome differs between a BRD-affected (n = 56) and visually healthy (n = 73) Holstein steers. Fungal nasal community was determined by using Internal Transcribed Spacer (ITS) sequencing.

Results

The phyla, Ascomycota and Basidiomycota, and the genera, Trichosporon and Issatchenkia, were the most abundant among all animals, regardless of health status. We identified differences between healthy and BRD animals in abundance of Trichosporon and Issatchenkia orientalis at a sub-species level that could be a potential indicator of BRD. No differences were observed in the nasal fungal alpha and beta diversity between BRD and healthy animals. However, the fungal community structure was affected based on season, specifically when comparing samples collected in the summer to the winter season. We then performed a random forest model, based on the fungal community and abundance of the BRD-pathobionts (qPCR data generated from a previous study using the same animals), to classify healthy and BRD animals and determine the agreement with visual diagnosis. Classification of BRD or healthy animals using ITS sequencing was low and agreed with the visual diagnosis with an accuracy of 51.9%. A portion of the ITS-predicted BRD animals were not predicted based on the abundance of BRD pathobionts. Lastly, fungal and bacterial co-occurrence were more common in BRD animals than healthy animals.

Discussion

The results from this novel study provide a baseline understanding of the fungal diversity and composition in the nasal cavity of BRD and healthy animals, upon which future interaction studies, including other nasal microbiome members to further understand and accurately diagnose BRD, can be designed.

Fungi and cancer

The microbiome may impact cancer development, progression and treatment responsiveness, but its fungal components remain insufficiently studied in this context. In this review, we highlight accumulating evidence suggesting a possible involvement of commensal and pathogenic fungi in modulation of cancer-related processes. We discuss the mechanisms by which fungi can influence tumour biology, locally by activity exerted within the tumour microenvironment, or remotely through secretion of bioactive metabolites, modulation of host immunity and communications with neighbouring bacterial commensals. We examine prospects of utilising fungi-related molecular signatures in cancer diagnosis, patient stratification and assessment of treatment responsiveness, while highlighting challenges and limitations faced in performing such research. In all, we demonstrate that fungi likely constitute important members of mucosal and tumour-residing microbiomes. Exploration of fungal inter-kingdom interactions with the bacterial microbiome and the host and decoding of their causal impacts on tumour biology may enable their harnessing into cancer diagnosis and treatment.

Bacterial-fungal interactions and their impact on microbial pathogenesis

Microbial communities of the human microbiota exhibit diverse effects on human health and disease. Microbial homeostasis is important for normal physiological functions and changes to the microbiota are associated with many human diseases including diabetes, cancer, and colitis. In addition, there are many microorganisms that are either commensal or acquired from environmental reservoirs that can cause diverse pathologies. Importantly, the balance between health and disease is intricately connected to how members of the microbiota interact and affect one another's growth and pathogenicity. However, the mechanisms that govern these interactions are only beginning to be understood. In this review, we outline bacterial-fungal interactions in the human body, including examining the mechanisms by which bacteria govern fungal growth and virulence, as well as how fungi regulate bacterial pathogenesis. We summarize advances in the understanding of chemical, physical, and protein-based interactions, and their role in exacerbating or impeding human disease. We focus on the three fungal species responsible for the majority of systemic fungal infections in humans: Candida albicans, Cryptococcus neoformans, and Aspergillus fumigatus. We conclude by summarizing recent studies that have mined microbes for novel antimicrobials and antivirulence factors, highlighting the potential of the human microbiota as a rich resource for small molecule discovery.

Changes in the gut microbiota of rats after exposure to the fungicide Mancozeb

Mancozeb is a fungicide commonly used in pest control programs, especially to protect vineyards. Its toxicity has already been evidenced in several studies. However, its influence on the composition and diversity of the gut microbiota remains unknown. In this work, the adverse impact of Mancozeb on the intestinal microbiota was investigated using a rodent model. Adult male Sprague Dawley rats were randomized into three groups: Control (standard diet), MZ1 (Mancozeb dose: 250 mg/kg bw/day), and MZ2 (Mancozeb dose: 500 mg/kg bw/day). After 12 weeks of experiment, animals were euthanized, and feces present in the intestine were collected. After fecal DNA extraction, the V4 region of the 16S rRNA gene was amplified followed by sequencing in an Ion S5™ System. Alpha and beta diversity analysis showed significant differences between Control and Mancozeb groups (MZ1 e MZ2), but no difference between MZ1 and MZ2 was observed. Seven genera significantly increased in abundance following Mancozeb exposure, while five genera decreased. Co-occurrence analyses revealed that the topological properties of the microbial networks, which can be used to infer co-occurrence interaction patterns among microorganisms, were significantly lower in both groups exposed to Mancozeb when compared to Control. In addition, 23 differentially abundant microbial metabolic pathways were identified in Mancozeb-treated groups mainly related to a change in energy metabolism, LPS biosynthesis, and nucleotide biosynthesis. In conclusion, the exposure to Mancozeb presented side effects by changing the composition of the microbiota in rats, increasing bacterial diversity regardless of the dose used, reducing the interaction patterns of the microbial communities, and changing microbial metabolic pathways.

Development of gut mycobiome in infants and young children: a prospective cohort study

BACKGROUND

The composition of the gut fungal microbiome, mycobiome, is likely associated with human health. Yet, the development of gut mycobiome is poorly understood in infants and children. Here we investigate how perinatal events influence the development of gut mycobiome.

METHODS

In this prospective cohort study of 140 infants, we used ITS gene sequencing of fecal samples from birth to the age of 18 months. We compared gut mycobiome composition according to delivery mode and exposure to intrapartum antibiotics during vaginal delivery.

RESULTS

At birth, gut mycobiome were dominated by the genus Candida, at 6-month stool samples by Malassezia and Cystofilobasidium, and the 18-month stool samples by Trichosporon and unidentified fungi. Perinatal factors altered mycobiome. At 18 months, gut mycobiome of infants born vaginally consisted mostly of Trichosporon (32%) and unidentified fungi (31%), while those born via Cesarean section delivery samples had mycobiome dominated by Saccharomyces (50%). At the age of 18 months, those exposed to intrapartum antibiotics had mycobiome dominated by Trichosporon (66%) not seen in those unexposed to antibiotics.

CONCLUSIONS

Delivery mode and exposure to intrapartum antibiotic prophylaxis were markedly associated with gut mycobiome composition from birth to 18 months of age.

IMPACT

The composition of the gut mycobiome is likely associated with human health. Yet, the development of gut mycobiome is poorly understood in infants and children. In this prospective cohort study, delivery mode and exposure to intrapartum antibiotic prophylaxis were markedly associated with gut mycobiome composition from birth to 18 months of age. The impact of intrapartum antibiotic prophylaxis on fungal microbiome in vaginally born infants, previously shown to influence gut bacteriome composition, may be explained by the interaction between bacteria and fungi. Gut mycobiome composition likely deserves further investigation in relation to gut microbiome and health in children.

Fungal-Bacterial Interactions in the Human Gut of Healthy Individuals

Most studies of the microbiota in the human gut focus on the bacterial part, but increasing information shows that intestinal fungi are also important for maintaining health. This can be either by directly influencing the host or by indirectly influencing the gut bacteria that link to host health. Studies of fungal communities in large cohorts are scarce; therefore, this study aims at obtaining more insight into the mycobiome of healthy individuals and how this mycobiome interacts with the bacterial component of the microbiome. For this purpose, ITS2 and 16S rRNA gene amplicon sequencing was performed on fecal samples from 163 individuals which were available from two separate studies to analyze the fungal and bacterial microbiome, respectively, as well as the cross-kingdom interactions. The results showed a much lower fungal, as compared to bacterial, diversity. Ascomycota and Basidiomycota were the dominant fungal phyla across all the samples, but levels varied enormously between individuals. The ten most abundant fungal genera were Saccharomyces, Candida, Dipodascus, Aureobasidium, Penicillium, Hanseniaspora, Agaricus, Debaryomyces, Aspergillus, and Pichia, and here also extensive inter-individual variation was observed. Correlations were made between bacteria and fungi, and only positive correlations were observed. One of the correlations was between Malassezia restricta and the genus Bacteroides, which have both been previously described as alleviated in IBD. Most of the other correlations found were with fungi that are not known as gut colonizers but originate from food and the environment. To further investigate the importance of the observed correlations found, more research is needed to discriminate between gut colonizers and transient species.

Neglected gut microbiome: interactions of the non-bacterial gut microbiota with enteric pathogens

A diverse array of commensal microorganisms inhabits the human intestinal tract. The most abundant and most studied members of this microbial community are undoubtedly bacteria. Their important role in gut physiology, defense against pathogens, and immune system education has been well documented over the last decades. However, the gut microbiome is not restricted to bacteria. It encompasses the entire breadth of microbial life: viruses, archaea, fungi, protists, and parasitic worms can also be found in the gut. While less studied than bacteria, their divergent but important roles during health and disease have become increasingly more appreciated. This review focuses on these understudied members of the gut microbiome. We will detail the composition and development of these microbial communities and will specifically highlight their functional interactions with enteric pathogens, such as species of the family Enterobacteriaceae. The interactions can be direct through physical interactions, or indirect through secreted metabolites or modulation of the immune response. We will present general concepts and specific examples of how non-bacterial gut communities modulate bacterial pathogenesis and present an outlook for future gut microbiome research that includes these communities.

Dual transcriptome of Streptococcus mutans and Candida albicans interplay in biofilms

Objective

To assess the interactions between Streptococcus mutans and Candida albicans during cariogenic biofilm formation.

Methods

The S. mutans and C. albicans duo-species biofilms were formed in 1% sucrose to mimic the high caries risk challenges. The biofilm structure was assessed using two-photon laser confocal microscopy. The transcriptome of 48h-biofilms was assessed by RNA-Seq. The expression of S. mutans and C. albicans virulence genes was examined via real-time reverse transcription-polymerase chain reaction.

Results

The morphogenesis of C. albicans-S. mutans duo-species biofilms was significantly altered when comparing to S. mutans or C. albicans single-species biofilm. Duo-species biofilms exhibited unique expression profile with a large number of differentially expressed genes (DEGs), including a higher expression of S. mutans atpD (acid-adaptive), C. albicans CHT2 (fungal cell wall chitin remodeling), and C. albicans SOD3 (cytotoxic oxygen radical destroying) (p < 0.05). KEGG pathway analyses further revealed that the majority of the up-regulated DEGs are related to microbial metabolism. Furthermore, the expressions of S. mutans and C. albicans key virulence genes (gtfB, gtfC, gtfD, ECE1, HWP1, ERG4, CHT2) were associated with sugar availability-related and time-related dynamics.

Conclusion

Cross-kingdom interactions impact S. mutans-C. albicans biofilm formations and dynamic expressions of virulence genes.

Assessing the causes and consequences of gut mycobiome variation in a wild population of the Seychelles warbler

BACKGROUND

Considerable research has focussed on the importance of bacterial communities within the vertebrate gut microbiome (GM). However, studies investigating the significance of other microbial kingdoms, such as fungi, are notably lacking, despite their potential to influence host processes. Here, we characterise the fungal GM of individuals living in a natural population of Seychelles warblers (Acrocephalus sechellensis). We evaluate the extent to which fungal GM structure is shaped by environment and host factors, including genome-wide heterozygosity and variation at key immune genes (major histocompatibility complex (MHC) and Toll-like receptor (TLR)). Importantly, we also explore the relationship between fungal GM differences and subsequent host survival. To our knowledge, this is the first time that the genetic drivers and fitness consequences of fungal GM variation have been characterised for a wild vertebrate population.

RESULTS

Environmental factors, including season and territory quality, explain the largest proportion of variance in the fungal GM. In contrast, neither host age, sex, genome-wide heterozygosity, nor TLR3 genotype was associated with fungal GM differences in Seychelles warblers. However, the presence of four MHC-I alleles and one MHC-II allele was associated with changes in fungal GM alpha diversity. Changes in fungal richness ranged from between 1 and 10 sequencing variants lost or gained; in some cases, this accounted for 20% of the fungal variants carried by an individual. In addition to this, overall MHC-I allelic diversity was associated with small, but potentially important, changes in fungal GM composition. This is evidenced by the fact that fungal GM composition differed between individuals that survived or died within 7 months of being sampled.

CONCLUSIONS

Our results suggest that environmental factors play a primary role in shaping the fungal GM, but that components of the host immune system-specifically the MHC-may also contribute to the variation in fungal communities across individuals within wild populations. Furthermore, variation in the fungal GM can be associated with differential survival in the wild. Further work is needed to establish the causality of such relationships and, thus, the extent to which components of the GM may impact host evolution. Video Abstract.

Opportunities for growth in the growing field of psychobiotics

There is growing interest in the field of psychobiotics, which are probiotics that confer a mental health benefit when ingested. As this field grows, it should pay particular attention to three areas within psychobiotics research that are currently under-studied - sex (and gender) representation, fungi and the mycobiome, and vagus nerve activity. Giving these three domains more attention is currently feasible without significant increased investment of time or money. We discuss these three domains briefly, why they are of particular relevance for psychobiotics research, and how psychobiotics research can easily integrate their perspectives. Our recommendations are summarised in the conclusion, but include equal sex representation at all phases of research (human and animal studies), investigating the relationship between psychobiotics and commensal fungi, and measuring the activity of the vagus nerve in psychobiotics studies.

Mycobiota and diet-derived fungal xenosiderophores promote Salmonella gastrointestinal colonization

The fungal gut microbiota (mycobiota) has been implicated in diseases that disturb gut homeostasis, such as inflammatory bowel disease. However, little is known about functional relationships between bacteria and fungi in the gut during infectious colitis. Here we investigated the role of fungal metabolites during infection with the intestinal pathogen Salmonella enterica serovar Typhimurium, a major cause of gastroenteritis worldwide. We found that, in the gut lumen, both the mycobiota and fungi present in the diet can be a source of siderophores, small molecules that scavenge iron from the host. The ability to use fungal siderophores, such as ferrichrome and coprogen, conferred a competitive growth advantage to Salmonella strains expressing the fungal siderophore receptors FhuA or FhuE in vitro and in a mouse model. Our study highlights the role of inter-kingdom cross-feeding between fungi and Salmonella and elucidates an additional function of the gut mycobiota, revealing the importance of these understudied members of the gut ecosystem during bacterial infection.

Fungal exposome, human health, and unmet needs: A 2022 update with special focus on allergy

Humans inhale, ingest, and touch thousands of fungi each day. The ubiquity and diversity of the fungal kingdom, reflected by its complex taxonomy, are in sharp contrast with our scarce knowledge about its distribution, pathogenic effects, and effective interventions at the environmental and individual levels. Here, we present an overview of salient features of fungi as permanent players of the human exposome and key determinants of human health, through the lens of fungal allergy and other fungal hypersensitivity reactions. Improved understanding of the fungal exposome sheds new light on the epidemiology of fungal-related hypersensitivity diseases, their immunological substratum, the currently available methods, and biomarkers for environmental and medical fungi. Unmet needs are described and potential approaches are highlighted as perspectives.

Interkingdom assemblages in human saliva display group-level surface mobility and disease-promoting emergent functions

Fungi and bacteria form multicellular biofilms causing many human infections. How such distinctive microbes act in concert spatiotemporally to coordinate disease-promoting functionality remains understudied. Using multiscale real-time microscopy and computational analysis, we investigate the dynamics of fungal and bacterial interactions in human saliva and their biofilm development on tooth surfaces. We discovered structured interkingdom assemblages displaying emergent functionalities to enhance collective surface colonization, survival, and growth. Further analyses revealed an unexpected group-level surface mobility with coordinated “leaping-like” and “walking-like” motions while continuously growing. These mobile groups of growing cells promote rapid spatial spreading of both species across surfaces, causing more extensive tooth decay. Our findings show multicellular interkingdom assemblages acting like supraorganisms with functionalities that cannot be achieved without coassembly.

Fungi and bacteria often engage in complex interactions, such as the formation of multicellular biofilms within the human body. Knowledge about how interkingdom biofilms initiate and coalesce into higher-level communities and which functions the different species carry out during biofilm formation remain limited. We found native-state assemblages of Candida albicans (fungi) and Streptococcus mutans (bacteria) with highly structured arrangement in saliva from diseased patients with childhood tooth decay. Further analyses revealed that bacterial clusters are attached within a network of fungal yeasts, hyphae, and exopolysaccharides, which bind to surfaces as a preassembled cell group. The interkingdom assemblages exhibit emergent functions, including enhanced surface colonization and growth rate, stronger tolerance to antimicrobials, and improved shear resistance, compared to either species alone. Notably, we discovered that the interkingdom assemblages display a unique form of migratory spatial mobility that enables fast spreading of biofilms across surfaces and causes enhanced, more extensive tooth decay. Using mutants, selective inactivation of species, and selective matrix removal, we demonstrate that the enhanced stress resistance and surface mobility arise from the exopolymeric matrix and require the presence of both species in the assemblage. The mobility is directed by fungal filamentation as hyphae extend and contact the surface, lifting the assemblage with a “forward-leaping motion.” Bacterial cell clusters can “hitchhike” on this mobile unit while continuously growing, to spread across the surface three-dimensionally and merge with other assemblages, promoting community expansion. Together, our results reveal an interkingdom assemblage in human saliva that behaves like a supraorganism, with disease-causing emergent functionalities that cannot be achieved without coassembly.

A common vesicle proteome drives fungal biofilm development

Candida species are commensal organisms commonly interacting in the same host niche. In the pathogenic state, they frequently grow as a biofilm, often in mixed infections. The present studies observe a reliance upon common extracellular vesicle cargo for biofilm structure and function supporting interactions among species. The results reveal a vesicle cargo-driven coordination among Candida species during biofilm formation.

Extracellular vesicles mediate community interactions among cells ranging from unicellular microbes to complex vertebrates. Extracellular vesicles of the fungal pathogen Candida albicans are vital for biofilm communities to produce matrix, which confers environmental protection and modulates community dispersion. Infections are increasingly due to diverse Candida species, such as the emerging pathogen Candida auris, as well as mixed Candida communities. Here, we define the composition and function of biofilm-associated vesicles among five species across the Candida genus. We find similarities in vesicle size and release over the biofilm lifespan. Whereas overall cargo proteomes differ dramatically among species, a group of 36 common proteins is enriched for orthologs of C. albicans biofilm mediators. To understand the function of this set of proteins, we asked whether mutants in select components were important for key biofilm processes, including drug tolerance and dispersion. We found that the majority of these cargo components impact one or both biofilm processes across all five species. Exogenous delivery of wild-type vesicle cargo returned mutant phenotypes toward wild type. To assess the impact of vesicle cargo on interspecies interactions, we performed cross-species vesicle addition and observed functional complementation for both biofilm phenotypes. We explored the biologic relevance of this cross-species biofilm interaction in mixed species and mutant studies examining the drug-resistance phenotype. We found a majority of biofilm interactions among species restored the community’s wild-type behavior. Our studies indicate that vesicles influence the development of protective monomicrobial and mixed microbial biofilm communities.

Insight into the Relationship between Oral Microbiota and the Inflammatory Bowel Disease

Inflammatory bowel disease has been a growing concern of lots of people globally, including both adults and children. As a chronic inflammatory disease of the intestine, even though the etiology of inflammatory bowel disease is still unclear, the available evidence from clinic observations has suggested a close association with microorganisms. The oral microbiota possesses the characteristics of a large number and abundant species, second only to the intestinal microbiota in the human body; as a result, it successfully attracts the attention of researchers. The highly diverse commensal oral microbiota is not only a normal part of the oral cavity but also has a pronounced impact on the pathophysiology of general health. Numerous studies have shown the potential associations between the oral microbiota and inflammatory bowel disease. Inflammatory bowel disease can affect the composition of the oral microbiota and lead to a range of oral pathologies. In turn, there are a variety of oral microorganisms involved in the development and progression of inflammatory bowel disease, including Streptococcus spp., Fusobacterium nucleatum, Porphyromonas gingivalis, Campylobacter concisus, Klebsiella pneumoniae, Saccharibacteria (TM7), and Candida albicans. Based on the above analysis, the purpose of this review is to summarize this relationship of mutual influence and give further insight into the detection of flora as a target for the diagnosis and treatment of inflammatory bowel disease to open up a novel approach in future clinical practice.

Microbiota succession throughout life from the cradle to the grave

Associations between age and the human microbiota are robust and reproducible. The microbial composition at several body sites can predict human chronological age relatively accurately. Although it is largely unknown why specific microorganisms are more abundant at certain ages, human microbiota research has elucidated a series of microbial community transformations that occur between birth and death. In this Review, we explore microbial succession in the healthy human microbiota from the cradle to the grave. We discuss the stages from primary succession at birth, to disruptions by disease or antibiotic use, to microbial expansion at death. We address how these successions differ by body site and by domain (bacteria, fungi or viruses). We also review experimental tools that microbiota researchers use to conduct this work. Finally, we discuss future directions for studying the microbiota's relationship with age, including designing consistent, well-powered, longitudinal studies, performing robust statistical analyses and improving characterization of non-bacterial microorganisms.

FunOMIC: Pipeline with built-in fungal taxonomic and functional databases for human mycobiome profiling

While analysis of the bacterial microbiome has become routine, that of the fungal microbiome is still hampered by the lack of robust databases and bioinformatic pipelines. Here, we present FunOMIC, a pipeline with built-in taxonomic (1.6 million marker genes) and functional (3.4 million non-redundant fungal proteins) databases for the identification of fungi. Applied to more than 2,600 human metagenomic samples, the tool revealed fungal species associated with geography, body sites, and diseases. Correlation network analysis provided new insights into inter-kingdom interactions. With this pipeline and two of the most comprehensive fungal databases, we foresee a fast-growing resource for mycobiome studies.

Cross-Kingdom Infection of Macrophages Reveals Pathogen- and Immune-Specific Global Reprogramming and Adaptation

The relationship between the human microbiota and infectious disease outcome is a rapidly expanding area of study. Understanding how the host responds to changes in its symbiotic relationship with microbes provides new insight into how disruption can promote disease.

Association between intestinal microbiota and inflammatory bowel disease

Inflammatory bowel disease (IBD), which includes Crohn's disease (CD) and ulcerative colitis (UC), has emerged as a global disease with high incidence, long duration, devastating clinical symptoms, and low curability (relapsing immune response and barrier function defects). Mounting studies have been performed to investigate its pathogenesis to provide an ever‐expanding arsenal of therapeutic options, while the precise etiology of IBD is not completely understood yet. Recent advances in high‐throughput sequencing methods and animal models have provided new insights into the association between intestinal microbiota and IBD. In general, dysbiosis characterized by an imbalanced microbiota has been widely recognized as a pathology of IBD. However, intestinal microbiota alterations represent the cause or result of IBD process remains unclear. Therefore, more evidences are needed to identify the precise role of intestinal microbiota in the pathogenesis of IBD. Herein, this review aims to outline the current knowledge of commonly used, chemically induced, and infectious mouse models, gut microbiota alteration and how it contributes to IBD, and dysregulated metabolite production links to IBD pathogenesis.

The Mycobiome: Cancer Pathogenesis, Diagnosis, and Therapy

Cancer is among the leading causes of death globally. Despite advances in cancer research, a full understanding of the exact cause has not been established. Recent data have shown that the microbiome has an important relationship with cancer on various levels, including cancer pathogenesis, diagnosis and prognosis, and treatment. Since most studies have focused only on the role of bacteria in this process, in this article we review the role of fungi-another important group of the microbiome, the totality of which is referred to as the "mycobiome"-in the development of cancer and how it can impact responses to anticancer medications. Furthermore, we provide recent evidence that shows how the different microbial communities interact and affect each other at gastrointestinal and non-gastrointestinal sites, including the skin, thereby emphasizing the importance of investigating the microbiome beyond bacteria.

Human Fungal Infection, Immune Response, and Clinical Challenge-a Perspective During COVID-19 Pandemic

Fungi are a small but important part of the human microbiota and several fungi are familiar to the immune system, yet certain can cause infections in immunocompromised hosts and referred as opportunistic pathogens. The fungal coinfections in COVID-19 hosts with predisposing conditions and immunosuppressive medications are posing higher severity and death. The immunological counteraction (innate/adaptive immunity) is triggered when the PRRs on the host cells recognize the fungal PAMPs. However, in simultaneous infections (COVID-19 and fungal coinfection), the synergism of TLR and NLR may hyperactivate the immune cells which dramatically increase the cytokine level and generate cytokine storm. Fungal colonization in the human gut assists the development of microbiome assembly, ecology, and shaping immune response. However, SARS-CoV-2 infection represented unstable mycobiomes and long-term dysbiosis in a large proportion in COVID-19 patients. Normally, amphotericin B is considered as first-line treatment for invasive fungal infection. So, amphotericin B therapy is recommended in COVID-19 hosts with serious fungal infections. Still, the long-term corticosteroid supplementation prescribed in case of severe pneumonia and lower oxygen levels may result in systemic fungal infection in COVID-19 patients, eventually limiting the lifesaving benefits of available medications. Also, due to the evolution of fungal resistance to available antibiotics, the current treatments are becoming ineffective. Therefore, this review summarizes the concerns, needed to deal with the impending crises.

Augmented Enterocyte Damage During Candida albicans and Proteus mirabilis Coinfection

The human gut acts as the main reservoir of microbes and a relevant source of life-threatening infections, especially in immunocompromised patients. There, the opportunistic fungal pathogen Candida albicans adapts to the host environment and additionally interacts with residing bacteria. We investigated fungal-bacterial interactions by coinfecting enterocytes with the yeast Candida albicans and the Gram-negative bacterium Proteus mirabilis resulting in enhanced host cell damage. This synergistic effect was conserved across different P. mirabilis isolates and occurred also with non-albicans Candida species and C. albicans mutants defective in filamentation or candidalysin production. Using bacterial deletion mutants, we identified the P. mirabilis hemolysin HpmA to be the key effector for host cell destruction. Spatially separated coinfections demonstrated that synergism between Candida and Proteus is induced by contact, but also by soluble factors. Specifically, we identified Candida-mediated glucose consumption and farnesol production as potential triggers for Proteus virulence. In summary, our study demonstrates that coinfection of enterocytes with C. albicans and P. mirabilis can result in increased host cell damage which is mediated by bacterial virulence factors as a result of fungal niche modification via nutrient consumption and production of soluble factors. This supports the notion that certain fungal-bacterial combinations have the potential to result in enhanced virulence in niches such as the gut and might therefore promote translocation and dissemination.

Diet and Host Genetics Drive the Bacterial and Fungal Intestinal Metatranscriptome of Gilthead Sea Bream

The gut microbiota is now recognised as a key target for improving aquaculture profit and sustainability, but we still lack insights into the activity of microbes in fish mucosal surfaces. In the present study, a metatranscriptomic approach was used to reveal the expression of gut microbial genes in the farmed gilthead sea bream. Archaeal and viral transcripts were a minority but, interestingly and contrary to rRNA amplicon-based studies, fungal transcripts were as abundant as bacterial ones, and increased in fish fed a plant-enriched diet. This dietary intervention also drove a differential metatranscriptome in fish selected for fast and slow growth. Such differential response reinforced the results of previously inferred metabolic pathways, enlarging, at the same time, the catalogue of microbial functions in the intestine. Accordingly, vitamin and amino acid metabolism, and rhythmic and symbiotic processes were mostly shaped by bacteria, whereas fungi were more specifically configuring the host immune, digestive, or endocrine processes.