Two numerically important bacteria in marine pulp mill effluent enrichment cultures were isolated. These organisms were gram-negative, rod-shaped, strictly aerobic bacteria. Isolate IRE-31T (T = type strain) produced hydrolytic enzymes for the breakdown of cellulose, xylan, chitin, gelatin, and Tween 80. It also utilized a variety of monosaccharides, disaccharides, amino acids, and volatile fatty acids for growth. Isolate KW-40T did not utilize natural polymers, but it could grow on a variety of monosaccharides, disaccharides, alcohols, and amino acids. It also utilized methanol and aromatic compounds. The surfaces of both organisms were covered by blebs and vesicles. 16S rRNA analyses placed both organisms in the gamma-3 subclass of the phylum Proteobacteria. They were related to Oceanospirillum linum, Marinomonas vaga, Pseudomonas putida, and Halomonas elongata, although a close association with any of these bacteria was not found. The guanine-plus-cytosine contents of strain IRE-31T and KW-40T were 57.6 and 54.9 mol%, respectively. On the basis of 16S rRNA sequence and phenotypic characterizations, these isolates were different enough so that they could be considered members of new genera. Thus, the following two new genera and species are proposed: Microbulbifer hydrolyticus, with type strain IRE-31 (= ATCC 700072), and Marinobacterium georgiense, with type strain KW-40 (= ATCC 700074).