One of the most significant and evolutionary relevant challenges in the origins of multicellular eukaryotes is how these organisms survived in a bacterial laden world. Animals and bacteria have…

The National Aeronautics and Space Administration (NASA) awarded a $351,186.25 grant to New Mexico State University (NMSU) for a research project related to the evolutionary ecology of symbiosis between multicellular organisms and bacteria. The objectives are to examine how bacteria evolved under different environmental conditions affect their ability to infect native hosts, measure host immune response to native and non-native bacteria, and determine how abiotic factors impact the fitness of the symbiosis. This grant is part of NASA's Exobiology mission to understand the early evolution of multicellular life and the biosphere. The work will provide insights into how complex multicellular animals with innate immune systems evolved with beneficial microbes. This grant does not have a set-aside designation.

One of the most significant and evolutionary relevant challenges in the origins of multicellular eukaryotes is how these organisms survived in a bacterial laden world. Animals and bacteria have evolved together since the appearance of the first eukaryotes through shared ecological niches or symbiotic relationships. Most of these symbiotic relationships are unique in that they allow the exploitation of challenging ecological niches that neither host nor symbiont can survive on their own. In many of these associations the host interactstransiently with the symbiont or bacterial consortium, whereas other symbioses are much more stable and specific, reflecting a true physiological or metabolic dependence on each other. In these types of associations, the capabilities of the holobiome (host + symbiont) gives them the ability to form new metabolic machinery that is beneficial to both partners. The proposed work aims at determining the effects of environmental factors on the evolutionary ecology of symbiosis, whether environmental conditions affect the overall fitness of the association, and how a multicellular hosts immune system responds to symbionts that evolved under different environmental conditions. We will determine how hosts respond (their ability to recognize and select beneficial bacteria) to native, nonnative, and experimentally evolved bacteria, and whether they are able to differentiate between strains that are less competent than others. We will use the well-established bobtail squid-vibrio bacteria beneficial association as the symbiosis model to measure how host recognition accommodates changes in the symbiont population, as well as whether vibrio bacteria that are affected by changes in abiotic (environmental) conditions are less able to colonize native squid hosts. The specific objectives of the proposed research include: 1) examine whether bacteria evolved under different abiotic conditions are more or less capable of infecting native squid hosts; 2) measure host immunological response to native, non-native, and experimentally evolved vibrios to determine how the host immune system recognizes and differentiates closely related symbiotic bacteria; 3) determine whether specific abiotic variables affect the fitness of the symbiosis by assessing how squid host and introduced vibrio persist over time. The methods utilized to complete these objectives will include experimentally evolving vibrio bacteria under different abiotic conditions (salinity, temperature, UV, and PH) in vitro and subsequently introducing the evolved strains to naive squid hosts to measure symbiont competency and host immune response. We plan to examine any changes in vibrio phenotype (growth, biofilm formation, host colonization) as well as genotype (through RNA SEQ and illumina sequencing of targeted symbiotic genes). Symbiotic bacteria that demonstrate phenotypes that are more favorable than others will be screened genetically to determine if specific genes are responsible for both host immune changes as well as the increase in fitness of the symbionts. Likewise, host response and subsequent fitness will be assessed measuring specific immunological components (e.g., pattern recognition receptors and effector molecules) and responses (binding, phagocytosis) to determine if vibrios that are less competent are recognized and rejected compared to wild type vibrios. The work proposed here is relevant to the NASA exobiology mission to understand the early evolution of multicellular life and the biosphere. Understanding how complex multicellular animals with innate immune systems evolved with bacteria in a beneficial manner will provide insight as to how advanced eukaryotes were able to infiltrate new habitats and acquire novel physiological capabilities due to the association with beneficial microbes. Additionally, this work will focus of how animal evolution has been guided by the presence of bacteria since their origins on early earth