UNITED STATES SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of The Securities Exchange Act of 1934

Date of Report (Date of Earliest Event Reported): July 17, 2013

METABOLIX, INC.

(Exact Name of Registrant as Specified in Charter)

21 Erie Street, Cambridge, Massachusetts 02139

(Address of Principal Executive Offices) (Zip Code)

Registrant’s telephone number, including area code: (617) 583-1700

(Former Name or Former Address, if Changed Since Last Report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions (see General Instruction A.2. below):

o Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

o Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

o Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

o Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Item 5.02. Departure of Directors or Certain Officers; Election of Directors; Appointment of Certain Officers; Compensatory Arrangements of Certain Officers.

(c) and (e)         On July 17, 2013, Metabolix, Inc. (the “Company”) announced that Johan van Walsem, currently the Company’s Vice President of Product Development and Manufacturing, will be promoted to the newly created position of Chief Operating Officer, effective as of July 22, 2013.

Mr. van Walsem has served as the Company’s Vice President of Manufacturing and Product Development since early 2012.  He returned to Metabolix in August 2009 as Vice President of Strategy and Commercial Development, following a16 month period as Senior Vice President, R&D and Bioprocessing at Joule Biotechnologies, a clean technology start-up company. Previously, Mr. van Walsem served as Metabolix’s Vice President of Manufacturing, Development and Operations from October 2003 until April 2008, and was Director of Manufacturing and Development from September 2001 to October 2003.

In connection with Mr. van Walsem’s promotion, the Company agreed to increase his base salary to $295,000 per year and to grant him a stock option under the Metabolix, Inc. 2006 Stock Option and Incentive Plan for the purchase of 100,000 shares of common stock of the Company at an exercise price equal to the Fair Market Value (as defined in the Plan) of the Company’s common stock on the date of grant, vesting in 16 equal quarterly installments over a period of four years from the date of commencement of his new role.

Item 7.01. Regulation FD Disclosure.

On July 17, 2013, the Company issued a press release announcing Mr. van Walsem’s promotion to Chief Operating Officer. The full text of this press release is furnished as Exhibit 99.1 to this Current Report on Form 8-K.

The information set forth in this Item 7.01 and Exhibit 99.1 attached hereto is intended to be furnished and shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended, or otherwise subject to the liabilities of that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933, as amended, or the Exchange Act, except as expressly set forth by specific reference in such filing.

Item 9.01. Financial Statements and Exhibits.

(d) Exhibits.

99.1 Press Release dated July 17, 2013

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SIGNATURE

Pursuant to the requirements of the Securities Exchange Act of 1934, the Registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

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EXHIBIT INDEX

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Exhibit 99.1

METABOLIX ANNOUNCES PROMOTION OF JOHAN VAN WALSEM

TO CHIEF OPERATING OFFICER

Cambridge, Massachusetts, July 17, 2013 – Metabolix, Inc. (NASDAQ: MBLX), an innovation-driven bioscience company delivering sustainable solutions to the plastics, chemicals and energy industries, announced today that Johan van Walsem has been promoted to the position of Chief Operating Officer (COO), effective Monday, July 22. In this newly created role, Mr. van Walsem will be responsible for the management of the Company’s biopolymers, biobased chemicals and crops businesses, as well as the key functional areas that enable these businesses to perform. He will continue to report to Metabolix President and Chief Executive Officer, Richard P. Eno.

“We are excited to appoint Johan to the position of COO of Metabolix, where he has taken on increasing levels of responsibility throughout his tenure,” said Mr. Eno. “He has led critical functions across each of our three business platforms: biopolymers, biobased chemicals and crops, and as a result, will be able to very effectively integrate our functional expertise for maximum commercial impact.

“During the past 16 months, we have redefined our biopolymer commercial strategy around high-value markets, set up global supply chains for biopolymers, built the initial customer base and advanced our manufacturing technology to lower overall costs,” Mr. Eno said. “We also have continued to achieve technical milestones in our biobased chemicals platform and have the potential to create a highly differentiated chemicals business. The creation of the chief operating officer role allows for clear focus on the execution of these businesses. I look forward to working together with Johan to drive further growth in the coming years.”

Mr. van Walsem most recently served as the Company’s Vice President of Manufacturing and Product Development. He has more than 20 years of experience in the processing industry, with more than 15 years’ experience leading development and manufacturing efforts for large-scale, fermentation-based processes. He also has been integral in the development of the manufacturing process for the Company’s Mirel biopolymer products. He received a Master’s degree in Chemical Engineering from the University of Pretoria in 1986 and an M.B.A. from the University of South Africa in 1995.

About Metabolix

Metabolix, Inc. is an advanced biomaterials company that is well positioned to address growing market demand for sustainable solutions in the plastics, chemicals and energy industries. The Company is developing and commercializing a family of high-performance biopolymers targeted to the markets for film and bag applications, performance additives and functional biodegradation. Metabolix’s biobased chemicals platform is focused on high-value segments and applications using its novel “FAST” recovery process. The Company also is developing a

platform for co-producing plastics, chemicals and energy from crops. Metabolix has established an industry-leading intellectual property portfolio that, together with its knowledge of advanced industrial practice, provides a foundation for industry collaborations.

For more information, please visit www.metabolix.com.

Safe Harbor for Forward-Looking Statements

This press release contains forward-looking statements which are made pursuant to the safe harbor provisions of Section 27A of the Securities Act of 1933, as amended, and Section 21E of the Securities Exchange Act of 1934, as amended. The forward-looking statements in this release do not constitute guarantees of future performance. Investors are cautioned that statements in this press release which are not strictly historical statements, including, without limitation, statements regarding expectations for the Company’s growth, constitute forward-looking statements. Such forward-looking statements are subject to a number of risks and uncertainties that could cause actual results to differ materially from those anticipated, including the risks and uncertainties detailed in Metabolix’s filings with the Securities and Exchange Commission. Metabolix assumes no obligation to update any forward-looking information contained in this press release or with respect to the announcements described herein.

(MBLX-G)

Metabolix Contact:

Lynne H. Brum, 617-682-4693, LBrum@metabolix.com

Media Inquiries:

Schwartz MSL Boston

Keith Giannini  781-684-0770 metabolix@schwartzmsl.com