1 Economically competitive commercial production of biodegradable bioplastics with desirable 2 properties is an important goal. In this study, we demonstrate the use of chromosome engineering 3 of an alternative bacterial host, Sinorhizobium meliloti, for production of the co-polymer, 4 poly(lactate-co-3-hydroxybutyrate). Codon-optimized genes for two previously engineered 5 enzymes, Clostridium propionicum propionate CoA transferase (Pct532 Cp ) and Pseudomonas sp. 6 MBEL 6-19

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... ate (PHA) synthase 1 (PhaC1400 Ps6-19 ), were introduced into S. 7 meliloti Rm1021 by chromosome integration, replacing the native phbC gene. Based on 8 phenotypic analysis and detection of polymer product by gas chromatography analysis, synthesis 9 and accumulation of the copolymer was confirmed. The chromosome integrant strain, with the 10 introduced genes under the control of the native phbC promoter, is able to produce over 15% cell 11 dry weight of poly(lactate-co-3-hydroxybutyrate), containing 30 mol% lactate, from growth on 12 mannitol. We were also able to purify the polymer from the culture and confirm the structure by 13 NMR and GC-MS. To our knowledge, this is the first demonstration of production of this 14 copolymer in the Alphaproteobacteria. Further optimization of this system may eventually yield 15 strains that are able to produce economically viable commercial product. 16 17