Species of the Alteromonas and Marinobacter genera are heterotrophic Gammaproteobacteria that are part of the marine microbial ecosystem. In this study, four strains were isolated from two nonaxenic Synechococcus cultures and were sequenced. Few studies of these two genera have been reported. Therefore, genomic data of Alteromonadaceae are valuable for the study of heterotroph-phototroph dynamics in marine bacterial communities.