The document discusses a study of the metabolic diversity of bacteria found in cocoons of the earthworm Eisenia fetida. Six bacterial isolates from the cocoons were tested for various metabolic traits. Most isolates tested positive for oxidase and citrate utilization, while one tested negative for oxidase and showed facultative anaerobic growth. This indicates there is metabolic diversity among the symbiotic bacteria in E. fetida cocoons. Further tests will help characterize each isolate and better understand their roles in the fitness and development of E. fetida.

1. Metabolic Diversity in Bacteria Associated with the Fitness of Earthworm Cocoons
Mark Walchuck and Jeremy Balster
Abstract
The cocoons of Eisenia fetida,a commonearthwormspecies,containdiverse populationsof symbiotic
bacteria. Bacterial speciesare foundinthe surroundingsoil orare passeddirectlyfromthe parent
earthwormtothe offspring. Itisimportanttounderstandthe behaviorof these symbiontsastheyare a
vital componentinthe fitnessof Eisenia fetida. The metabolicdiversityfoundamongstthe normal flora
extractedfromEisenia fetida cocoonsseemstoindicate thatthe microorganismshave specializedroles
inthe developmentof the immature earthworm. Diversityincharacteristicsof these microorganisms
alsomay indicate differencesintransmittance of thisnormal floraintothe cocoon. To determine
metabolicdiversity,cocoonswere selectedandsterilizedusingethanol. The contentswere then
squeezedontoindividual Petri dishescontainingtrypticsoyagar(TSA). These plateswere incubatedat
room temperature inmicroaerophilicconditions. Fromthese plates,six organismswere selectedbased
on colonymorphologyandisolatedontotheirownplates. Oxidase,citrate,andthioglycolate testswere
performedoneachof these six isolates. Of the six isolates,all butone testedpositive foroxidase,and
all isolatestestedpositive forcitrate utilization. Five of the six organismsshowedstrictlyaerobic
growth,while the sixthshowed facultativeanaerobicgrowth;thiswasthe same organismwhichwas
negative foroxidase. Fromthese results,itcanbe concludedthatdiversityinmetabolicbehaviordoes
existwithinthe symbiontpopulationof Eisenia fetida cocoons. Furthertestswill be performedto
reinforce these results,includinggramreactionsof the organismsandnitrate tests,whichwill provide
furtherinformationoneachorganism,leadingeventuallytoa betterunderstandingof eachorganism’s
effectonthe fitnessof Eisenia fetida.