Monoassociation with Lactobacillus plantarum Disrupts Intestinal Homeostasis in Adult Drosophila melanogaster.

Adult Drosophila melanogaster raised in the absence of symbiotic bacteria have fewer intestinal stem cell divisions and a longer life span than their conventionally reared counterparts. However, we do not know if increased stem cell divisions are essential for symbiont-dependent regulation of longevity. To determine if individual symbionts cause aging-dependent death in Drosophila, we examined the impacts of common symbionts on host longevity. We found that monoassociation of adult Drosophila with Lactobacillus plantarum, a widely reported fly symbiont and member of the probiotic Lactobacillus genus, curtails adult longevity relative to germfree counterparts. The effects of Lactobacillus plantarum on life span were independent of intestinal aging. Instead, we found that association with Lactobacillus plantarum causes an extensive intestinal pathology within the host, characterized by loss of stem cells, impaired epithelial renewal, and a gradual erosion of epithelial ultrastructure. Our study uncovers an unknown aspect of Lactobacillus plantarum-Drosophila interactions and establishes a simple model to characterize symbiont-dependent disruption of intestinal homeostasis.IMPORTANCE Under homeostatic conditions, gut bacteria provide molecular signals that support the organization and function of the host intestine. Sudden shifts in the composition or distribution of gut bacterial communities impact host receipt of bacterial cues and disrupt tightly regulated homeostatic networks. We used the Drosophila melanogaster model to determine the effects of prominent fly symbionts on host longevity and intestinal homeostasis. We found that monoassociation with Lactobacillus plantarum leads to a loss of intestinal progenitor cells, impaired epithelial renewal, and disruption of gut architecture as flies age. These observations uncover a novel phenotype caused by monoassociation of a germfree host with a common symbiont and establish a simple model to characterize symbiont-dependent loss of intestinal homeostasis.

Comparative evaluation of the genomes of three common Drosophila-associated bacteria.

Drosophila melanogaster is an excellent model to explore the molecular exchanges that occur between an animal intestine and associated microbes. Previous studies in Drosophila uncovered a sophisticated web of host responses to intestinal bacteria. The outcomes of these responses define critical events in the host, such as the establishment of immune responses, access to nutrients, and the rate of larval development. Despite our steady march towards illuminating the host machinery that responds to bacterial presence in the gut, there are significant gaps in our understanding of the microbial products that influence bacterial association with a fly host. We sequenced and characterized the genomes of three common Drosophila-associated microbes: Lactobacillus plantarum, Lactobacillus brevis and Acetobacter pasteurianus For each species, we compared the genomes of Drosophila-associated strains to the genomes of strains isolated from alternative sources. We found that environmental Lactobacillus strains readily associated with adult Drosophila and were similar to fly isolates in terms of genome organization. In contrast, we identified a strain of A. pasteurianus that apparently fails to associate with adult Drosophila due to an inability to grow on fly nutrient food. Comparisons between association competent and incompetent A. pasteurianus strains identified a short list of candidate genes that may contribute to survival on fly medium. Many of the gene products unique to fly-associated strains have established roles in the stabilization of host-microbe interactions. These data add to a growing body of literature that examines the microbial perspective of host-microbe relationships.

A deregulated intestinal cell cycle program disrupts tissue homeostasis without affecting longevity in Drosophila.

Recent studies illuminate a complex relationship between the control of stem cell division and intestinal tissue organization in the model system Drosophila melanogaster. Host and microbial signals drive intestinal proliferation to maintain an effective epithelial barrier. Although it is widely assumed that proliferation induces dysplasia and shortens the life span of the host, the phenotypic consequences of deregulated intestinal proliferation for an otherwise healthy host remain unexplored. To address this question, we genetically isolated and manipulated the cell cycle programs of adult stem cells and enterocytes. Our studies revealed that cell cycle alterations led to extensive cell death and morphological disruptions. Despite the extensive tissue damage, we did not observe an impact on longevity, suggesting a remarkable degree of plasticity in intestinal function.