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<!-- Creation Date      : 2021-03-01T21:25:52.5067077+00:00 -->
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  <xsd:element id="mcrb_ProceedsFromSecuritiesPurchaseAgreementNetOfIssuanceCostsRelatedParty" name="ProceedsFromSecuritiesPurchaseAgreementNetOfIssuanceCostsRelatedParty" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="mcrb_ProceedsFromAtTheMarketEquityOfferingNetOfCommissions" name="ProceedsFromAtTheMarketEquityOfferingNetOfCommissions" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="mcrb_ProceedsFromIssuanceOfCommonStockAndRestrictedCommonStock" name="ProceedsFromIssuanceOfCommonStockAndRestrictedCommonStock" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="mcrb_RestrictedInvestmentsPolicyTextBlock" name="RestrictedInvestmentsPolicyTextBlock" type="nonnum:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="mcrb_ResearchContractCostsAndAccrualsPolicyTextBlock" name="ResearchContractCostsAndAccrualsPolicyTextBlock" type="nonnum:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="mcrb_PatentCostsPolicyTextBlock" name="PatentCostsPolicyTextBlock" type="nonnum:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="mcrb_GrantRevenuePolicyTextBlock" name="GrantRevenuePolicyTextBlock" type="nonnum:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="mcrb_ScheduleOfAccruedExpenseAndOtherCurrentLiabilitiesTableTextBlock" name="ScheduleOfAccruedExpenseAndOtherCurrentLiabilitiesTableTextBlock" type="nonnum:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="mcrb_LesseeOperatingSubleasePaymentsToBeReceivedMaturityTableTextBlock" name="LesseeOperatingSubleasePaymentsToBeReceivedMaturityTableTextBlock" type="nonnum:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="mcrb_ScheduleOfOperatingLeaseAssetsAndLiabilitiesTableTextBlock" name="ScheduleOfOperatingLeaseAssetsAndLiabilitiesTableTextBlock" type="nonnum:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="mcrb_EntityIncorporationMonthAndYearOfIncorporation" name="EntityIncorporationMonthAndYearOfIncorporation" type="xbrli:gYearMonthItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="mcrb_NatureOfBusinessAndBasisOfPresentationLineItems" name="NatureOfBusinessAndBasisOfPresentationLineItems" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="mcrb_NatureOfBusinessAndBasisOfPresentationTable" name="NatureOfBusinessAndBasisOfPresentationTable" type="xbrli:stringItemType" substitutionGroup="xbrldt:hypercubeItem" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="mcrb_SER109Member" name="SER109Member" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="mcrb_UnderwrittenPublicOfferingMember" name="UnderwrittenPublicOfferingMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="mcrb_SecuritiesPurchaseAgreementMember" name="SecuritiesPurchaseAgreementMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="mcrb_SocieteDesProduitsNestleMember" name="SocieteDesProduitsNestleMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="mcrb_ConcurrentPlacementMember" name="ConcurrentPlacementMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="mcrb_NumberOfPatients" name="NumberOfPatients" type="xbrli:integerItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="mcrb_OptionToPurchaseAdditionalSharesOfCommonStock" name="OptionToPurchaseAdditionalSharesOfCommonStock" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="mcrb_CashCashEquivalentsAndShortAndLongTermInvestments" name="CashCashEquivalentsAndShortAndLongTermInvestments" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="mcrb_CashEquivalentsOriginalMaturityMaximumPeriod" name="CashEquivalentsOriginalMaturityMaximumPeriod" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="mcrb_AccountingPoliciesLineItems" name="AccountingPoliciesLineItems" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="mcrb_AccountingPoliciesTable" name="AccountingPoliciesTable" type="xbrli:stringItemType" substitutionGroup="xbrldt:hypercubeItem" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="mcrb_LaboratoryEquipmentMember" name="LaboratoryEquipmentMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="mcrb_FurnitureAndOfficeEquipmentMember" name="FurnitureAndOfficeEquipmentMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="mcrb_RevenueRecognizedRelatedToSalesBasedRoyalties" name="RevenueRecognizedRelatedToSalesBasedRoyalties" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="mcrb_RevenueRecognizedRelatedToMilestonePayments" name="RevenueRecognizedRelatedToMilestonePayments" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="mcrb_MinimumPercentageOfLikelihoodOfTaxBenefitBeingRealizedUponSettlement" name="MinimumPercentageOfLikelihoodOfTaxBenefitBeingRealizedUponSettlement" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="mcrb_AccruedDevelopmentAndClinicalManufacturingCostsCurrent" name="AccruedDevelopmentAndClinicalManufacturingCostsCurrent" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="mcrb_SubleaseAgreementMember" name="SubleaseAgreementMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="mcrb_OfficeLaboratoryAndManufacturingSpaceMember" name="OfficeLaboratoryAndManufacturingSpaceMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="mcrb_LesseeOperatingLeaseRemainingTermOfContract" name="LesseeOperatingLeaseRemainingTermOfContract" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="mcrb_LesseeOperatingSubleaseAnnualRentIncomeYearOne" name="LesseeOperatingSubleaseAnnualRentIncomeYearOne" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="mcrb_LesseeOperatingSubleaseAnnualRentIncomeYearTwo" name="LesseeOperatingSubleaseAnnualRentIncomeYearTwo" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="mcrb_LesseeOperatingSubleasePaymentsToBeReceivedNextTwelveMonths" name="LesseeOperatingSubleasePaymentsToBeReceivedNextTwelveMonths" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="mcrb_LesseeOperatingSubleasePaymentsToBeReceived" name="LesseeOperatingSubleasePaymentsToBeReceived" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="mcrb_SeveranceAndOtherTerminationBenefitsMember" name="SeveranceAndOtherTerminationBenefitsMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="mcrb_EmployeeSeveranceAndOtherBenefitsMember" name="EmployeeSeveranceAndOtherBenefitsMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="mcrb_AccruedExpensesAndOtherCurrentLiabilitiesMember" name="AccruedExpensesAndOtherCurrentLiabilitiesMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="mcrb_ProceedsFromIssuanceOfLongTermDebtGross" name="ProceedsFromIssuanceOfLongTermDebtGross" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="mcrb_DebtInstrumentTrancheOneMember" name="DebtInstrumentTrancheOneMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="mcrb_DebtInstrumentTrancheTwoMember" name="DebtInstrumentTrancheTwoMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="mcrb_DebtInstrumentTrancheThreeMember" name="DebtInstrumentTrancheThreeMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="mcrb_HerculesCapitalIncMember" name="HerculesCapitalIncMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="mcrb_LoanAndSecurityAgreementMember" name="LoanAndSecurityAgreementMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="mcrb_TermLoanFacilityMember" name="TermLoanFacilityMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="mcrb_CurrentLiabilityMember" name="CurrentLiabilityMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="mcrb_NonCurrentLiabilityMember" name="NonCurrentLiabilityMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="mcrb_PercentageOfPrepaymentAmountDuringFirstYearFollowingClosingDate" name="PercentageOfPrepaymentAmountDuringFirstYearFollowingClosingDate" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="mcrb_PercentageOfPrepaymentAmountDuringSecondYearFollowingClosingDate" name="PercentageOfPrepaymentAmountDuringSecondYearFollowingClosingDate" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="mcrb_PercentageOfPrepaymentAmountDuringThirdYearFollowingClosingDate" name="PercentageOfPrepaymentAmountDuringThirdYearFollowingClosingDate" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="mcrb_DebtInstrumentsPrepaymentPercentage" name="DebtInstrumentsPrepaymentPercentage" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="mcrb_DebtInstrumentPrepaymentCharges" name="DebtInstrumentPrepaymentCharges" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="mcrb_DebtInstrumentAdditionalAdvancePrepaymentsPercentage" name="DebtInstrumentAdditionalAdvancePrepaymentsPercentage" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="mcrb_AtTheMarketEquityOfferingProgramMember" name="AtTheMarketEquityOfferingProgramMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="mcrb_TwoThousandNineteenSalesAgreementMember" name="TwoThousandNineteenSalesAgreementMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="mcrb_TwoThousandNineteenAndTwoThousandTwentySalesAgreementMember" name="TwoThousandNineteenAndTwoThousandTwentySalesAgreementMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="mcrb_CowenAndCompanyLimitedLiabilityCompanyMember" name="CowenAndCompanyLimitedLiabilityCompanyMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="mcrb_UnderwritingAgreementMember" name="UnderwritingAgreementMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="mcrb_CowenAndCompanyLLCAndPiperSandlerCoMember" name="CowenAndCompanyLLCAndPiperSandlerCoMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="mcrb_PercentageOfCommissionOnSaleOfCommonStock" name="PercentageOfCommissionOnSaleOfCommonStock" type="xbrli:pureItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" />
  <xsd:element id="mcrb_GrossProceedsFromIssuanceOfCommonStock" name="GrossProceedsFromIssuanceOfCommonStock" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="mcrb_OptionExercisablePeriodForPurchaseAdditionalShares" name="OptionExercisablePeriodForPurchaseAdditionalShares" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="mcrb_SharebasedCompensationArrangementByShareBasedPaymentAwardStockOptionsTerm" name="SharebasedCompensationArrangementByShareBasedPaymentAwardStockOptionsTerm" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="mcrb_TwoThousandTwelveStockIncentivePlanMember" name="TwoThousandTwelveStockIncentivePlanMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="mcrb_PercentageCommonStockOutstandingShares" name="PercentageCommonStockOutstandingShares" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="mcrb_TwentyFifteenIncentivePlanMember" name="TwentyFifteenIncentivePlanMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="mcrb_TwoThousandFifteenEmployeeStockPurchasePlanMember" name="TwoThousandFifteenEmployeeStockPurchasePlanMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="mcrb_OfferingPeriodUnderThePlan" name="OfferingPeriodUnderThePlan" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="mcrb_PercentageOfPurchasePriceWithRespectToEachOfferingPeriod" name="PercentageOfPurchasePriceWithRespectToEachOfferingPeriod" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="mcrb_StockOptionsAndRestrictedStockUnitsMember" name="StockOptionsAndRestrictedStockUnitsMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="mcrb_MaximumDevelopmentMilestonePaymentsToBeReceived" name="MaximumDevelopmentMilestonePaymentsToBeReceived" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="mcrb_MaximumRegulatoryPaymentsToBeReceived" name="MaximumRegulatoryPaymentsToBeReceived" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="mcrb_MaximumAmountToBeReceivedOnAchievementOfCertainCommercialMilestones" name="MaximumAmountToBeReceivedOnAchievementOfCertainCommercialMilestones" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="mcrb_NestleHealthScienceMember" name="NestleHealthScienceMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="mcrb_PhaseTwoStudyMember" name="PhaseTwoStudyMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="mcrb_PhaseThreeStudyMember" name="PhaseThreeStudyMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="mcrb_PhaseTwoBStudyMember" name="PhaseTwoBStudyMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="mcrb_PhaseOneBStudyMember" name="PhaseOneBStudyMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="mcrb_ResearchCollaborationAndOptionAgreementMember" name="ResearchCollaborationAndOptionAgreementMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="mcrb_AstraZenecaIncorporatedMember" name="AstraZenecaIncorporatedMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="mcrb_CollaborativeArrangementUpfrontMilestonePaymentReceivable" name="CollaborativeArrangementUpfrontMilestonePaymentReceivable" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="mcrb_CollaborativeArrangementUpfrontLicenseFeeReceived" name="CollaborativeArrangementUpfrontLicenseFeeReceived" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="mcrb_TransactionPriceOfMilestonePaymentToBeReceived" name="TransactionPriceOfMilestonePaymentToBeReceived" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="mcrb_DeferredRevenueFromRelatedParty" name="DeferredRevenueFromRelatedParty" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="mcrb_MinimumExclusivityPeriod" name="MinimumExclusivityPeriod" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="mcrb_NumberOfInstallments" name="NumberOfInstallments" type="xbrli:integerItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="mcrb_OptionExercisePeriodFromExclusivityPeriod" name="OptionExercisePeriodFromExclusivityPeriod" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="mcrb_TermsOfDefinitiveLicenseAgreementGoodFaithNegotiationPeriod" name="TermsOfDefinitiveLicenseAgreementGoodFaithNegotiationPeriod" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="mcrb_OtherTermsOfDefinitiveLicenseAgreementPeriod" name="OtherTermsOfDefinitiveLicenseAgreementPeriod" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="mcrb_ResearchAgreementEffectiveTerminationDate" name="ResearchAgreementEffectiveTerminationDate" type="xbrli:dateItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="mcrb_NoticePeriodForTerminationOfAgreement" name="NoticePeriodForTerminationOfAgreement" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="mcrb_ResearchAndDevelopmentFixedConsideration" name="ResearchAndDevelopmentFixedConsideration" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="mcrb_ResearchAndDevelopmentEstimatedReimbursementCosts" name="ResearchAndDevelopmentEstimatedReimbursementCosts" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="mcrb_ResearchAndDevelopmentReimbursementCostsIncurred" name="ResearchAndDevelopmentReimbursementCostsIncurred" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="mcrb_ContractWithCustomerLiabilityWithRelatedPartyAdditions" name="ContractWithCustomerLiabilityWithRelatedPartyAdditions" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="mcrb_ContractWithCustomerLiabilityRevenueRecognizedWithRelatedParty" name="ContractWithCustomerLiabilityRevenueRecognizedWithRelatedParty" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="mcrb_ContractWithCustomerLiabilityWithRelatedParty" name="ContractWithCustomerLiabilityWithRelatedParty" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="mcrb_ContractWithCustomerLiabilityAdditions" name="ContractWithCustomerLiabilityAdditions" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="mcrb_UnvestedRestrictedStockUnitsMember" name="UnvestedRestrictedStockUnitsMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="mcrb_EmployeeStockPurchasePlanMember" name="EmployeeStockPurchasePlanMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="mcrb_LegalContingenciesMember" name="LegalContingenciesMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="mcrb_IncomeTaxDisclosureLineItems" name="IncomeTaxDisclosureLineItems" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="mcrb_IncomeTaxDisclosureTable" name="IncomeTaxDisclosureTable" type="xbrli:stringItemType" substitutionGroup="xbrldt:hypercubeItem" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="mcrb_OrphanDrugCreditCarryforwardMember" name="OrphanDrugCreditCarryforwardMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="mcrb_BeforeTwoThousandEighteenMember" name="BeforeTwoThousandEighteenMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="mcrb_AfterTwoThousandSeventeenMember" name="AfterTwoThousandSeventeenMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="mcrb_AfterTwoThousandSeventeenAndBeforeJanuaryOneTwoThousandTwentyOneMember" name="AfterTwoThousandSeventeenAndBeforeJanuaryOneTwoThousandTwentyOneMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="mcrb_AfterJanuaryOneTwoThousandTwentyOneMember" name="AfterJanuaryOneTwoThousandTwentyOneMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="mcrb_DeferredTaxAssetsCapitalizedOrganizationCosts" name="DeferredTaxAssetsCapitalizedOrganizationCosts" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="mcrb_DeferredTaxAssetsLeaseLiability" name="DeferredTaxAssetsLeaseLiability" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="mcrb_DeferredTaxAssetsDeferredExpenseCapitalizedResearchAndDevelopmentCosts" name="DeferredTaxAssetsDeferredExpenseCapitalizedResearchAndDevelopmentCosts" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="mcrb_DeferredTaxAssetsSection163JLimitationCARESAct" name="DeferredTaxAssetsSection163JLimitationCARESAct" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="mcrb_DeferredTaxLiabilitiesRightOfUseAssets" name="DeferredTaxLiabilitiesRightOfUseAssets" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="mcrb_TaxCreditCarryforwardExpirationYear" name="TaxCreditCarryforwardExpirationYear" type="xbrli:gYearItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="mcrb_OperatingLossCarryforwardsExpirationYear" name="OperatingLossCarryforwardsExpirationYear" type="xbrli:gYearItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="mcrb_NetOperatingLossesOnTaxableIncomeThresholdPercentage" name="NetOperatingLossesOnTaxableIncomeThresholdPercentage" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="mcrb_DecreaseInValuationAllowanceDeferredTaxAssetAmount" name="DecreaseInValuationAllowanceDeferredTaxAssetAmount" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="mcrb_IncreaseInValuationAllowanceDeferredTaxAsset" name="IncreaseInValuationAllowanceDeferredTaxAsset" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="mcrb_FlagshipPioneeringMember" name="FlagshipPioneeringMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="mcrb_SubLeaseCommencementDate" name="SubLeaseCommencementDate" type="xbrli:gYearMonthItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
</xsd:schema>
