ABSTRACT Microbes live in complex microniches within host tissues, but how symbiotic partners communicate to create such niches during development remains largely unexplored. Using confocal microscopy and symbiont genetics, we characterized the shaping of host microenvironments during light organ colonization of the squid Euprymna scolopes by the bacterium Vibrio fischeri . During embryogenesis, three pairs of invaginations form sequentially on the organ’s surface, producing pores that lead to interior compressed tubules at different stages of development. After hatching, these areas expand, allowing V. fischeri cells to enter and migrate ∼120 μm through three anatomically distinct regions before reaching blind-ended crypt spaces. A dynamic gatekeeper, or bottleneck, connects these crypts with the migration path. Once V. fischeri cells have entered the crypts, the bottlenecks narrow, and colonization by the symbiont population becomes spatially restricted. The actual timing of constriction and restriction varies with crypt maturity and with different V. fischeri strains. Subsequently, starting with the first dawn following colonization, the bottleneck controls a lifelong cycle of dawn-triggered expulsions of most of the symbionts into the environment and a subsequent regrowth in the crypts. Unlike other developmental phenotypes, bottleneck constriction is not induced by known microbe-associated molecular patterns (MAMPs) or by V. fischeri - produced bioluminescence, but it does require metabolically active symbionts. Further, while symbionts in the most mature crypts have a higher proportion of live cells and a greater likelihood of expulsion at dawn, they have a lower resistance to antibiotics. The overall dynamics of these distinct microenvironments reflect the complexity of the host-symbiont dialogue. IMPORTANCE The complexity, inaccessibility, and time scales of initial colonization of most animal microbiomes present challenges for the characterization of how the bacterial symbionts influence the form and function of tissues in the minutes to hours following the initial interaction of the partners. Here, we use the naturally occurring binary squid-vibrio association to explore this phenomenon. Imaging of the spatiotemporal landscape of this symbiosis during its onset provides a window into the impact of differences in both host-tissue maturation and symbiont strain phenotypes on the establishment of a dynamically stable symbiotic system. These data provide evidence that the symbionts shape the host-tissue landscape and that tissue maturation impacts the influence of strain-level differences on the daily rhythms of the symbiosis, the competitiveness for colonization, and antibiotic sensitivity.
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Maturation state of colonization sites promotes symbiotic resiliency in the Euprymna scolopes-Vibrio fischeri partnership
Many animals and plants acquire their coevolved symbiotic partners shortly post-embryonic development. Thus, during embryogenesis, cellular features must be developed that will promote both symbiont colonization of the appropriate tissues, as well as persistence at those sites. While variation in the degree of maturation occurs in newborn tissues, little is unknown about how this variation influences the establishment and persistence of host-microbe associations.
The binary symbiosis model, the squid-vibrio (
The data presented here provide evidence that the evolution of the squid-vibrio association has been selected for a nascent organ with a range of host tissue maturity at the onset of symbiosis. The resulting variation in physical and chemical environments results in a spectrum of host-symbiont interactions, notably, variation in susceptibility to environmental disturbance. This “insurance policy” provides resiliency to the symbiosis during the critical period of its early development. While differences in tissue maturity at birth have been documented in other animals, such as along the infant gut tract of mammals, the impact of this variation on host-microbiome interactions has not been studied. Because a wide variety of symbiosis characters are highly conserved over animal evolution, studies of the squid-vibrio association have the promise of providing insights into basic strategies that ensure successful bacterial passage between hosts in horizontally transmitted symbioses.
- NSF-PAR ID:
- 10404417
- Publisher / Repository:
- Springer Science + Business Media
- Date Published:
- Journal Name:
- Microbiome
- Volume:
- 11
- Issue:
- 1
- ISSN:
- 2049-2618
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract The binary association between the squid,
Euprymna scolopes , and its symbiont,Vibrio fischeri , serves as a model system to study interactions between beneficial bacteria and the innate immune system. Previous research demonstrated that binding of the squid's immune cells, hemocytes, toV. fischeri is altered if the symbiont is removed from the light organ, suggesting that host colonization alters hemocyte recognition ofV. fischeri . To investigate the influence of symbiosis on immune maturation during development, we characterized hemocyte binding and phagocytosis ofV. fischeri and nonsymbioticVibrio harveyi from symbiotic (sym) and aposymbiotic (apo) juveniles, and wild‐caught and laboratory‐raised sym and apo adults. Our results demonstrate that while light organ colonization byV. fischeri did not alter juvenile hemocyte response, these cells bound a similar number ofV. fischeri andV. harveyi yet phagocytosed onlyV. harveyi . Our results also indicate that long‐term colonization altered the adult hemocyte response toV. fischeri but notV. harveyi . All hemocytes from adult squid, regardless of apo or sym state, both bound and phagocytosed a similar number ofV. harveyi while hemocytes from both wild‐caught and sym‐raised adults bound significantly fewerV. fischeri , although moreV. fischeri were phagocytosed by hemocytes from wild‐caught animals. In contrast, hemocytes from apo‐raised squid bound similar numbers of bothV. fischeri andV. harveyi , although moreV. harveyi cells were engulfed, suggesting that blood cells from apo‐raised adults behaved similarly to juvenile hosts. Taken together, these data suggest that persistent colonization by the light organ symbiont is required for hemocytes to differentially bind and phagocytoseV. fischeri . The cellular immune system ofE. scolopes likely possesses multiple mechanisms at different developmental stages to promote a specific and life‐long interaction with the symbiont. -
ABSTRACT The European common cuttlefish, Sepia officinalis , is used extensively in biological and biomedical research, yet its microbiome remains poorly characterized. We analyzed the microbiota of the digestive tract, gills, and skin in mariculture-raised S. officinalis using a combination of 16S rRNA amplicon sequencing, quantitative PCR (qPCR), and fluorescence spectral imaging. Sequencing revealed a highly simplified microbiota consisting largely of two single bacterial amplicon sequence variants (ASVs) of Vibrionaceae and Piscirickettsiaceae . The esophagus was dominated by a single ASV of the genus Vibrio . Imaging revealed bacteria in the family Vibrionaceae distributed in a discrete layer that lines the esophagus. This Vibrio was also the primary ASV found in the microbiota of the stomach, cecum, and intestine, but occurred at lower abundance, as determined by qPCR, and was found only scattered in the lumen rather than in a discrete layer via imaging analysis. Treatment of animals with the commonly used antibiotic enrofloxacin led to a nearly 80% reduction of the dominant Vibrio ASV in the esophagus but did not significantly alter the relative abundance of bacteria overall between treated versus control animals. Data from the gills were dominated by a single ASV in the family Piscirickettsiaceae , which imaging visualized as small clusters of cells. We conclude that bacteria belonging to the Gammaproteobacteria are the major symbionts of the cuttlefish Sepia officinalis cultured from eggs in captivity and that the esophagus and gills are major colonization sites. IMPORTANCE Microbes can play critical roles in the physiology of their animal hosts, as evidenced in cephalopods by the role of Vibrio ( Aliivibrio ) fischeri in the light organ of the bobtail squid and the role of Alpha - and Gammaproteobacteria in the reproductive system and egg defense in a variety of cephalopods. We sampled the cuttlefish microbiome throughout the digestive tract, gills, and skin and found dense colonization of an unexpected site, the esophagus, by a microbe of the genus Vibrio , as well as colonization of gills by Piscirickettsiaceae . This finding expands the range of organisms and body sites known to be associated with Vibrio and is of potential significance for understanding host-symbiont associations, as well as for understanding and maintaining the health of cephalopods in mariculture.more » « less
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Summary A key regulatory decision for many bacteria is the switch between biofilm formation and motile dispersal, and this dynamic is well illustrated in the light‐organ symbiosis between the bioluminescent bacterium
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