A cluster of marine bacteria within the ␣-3 subclass of the class Proteobacteria accounted for up to 28% of the 16S ribosomal DNA (rDNA) sequences in seawater samples from the coast of the southeastern United States. Two independent oligonucleotide probes targeting 16S rDNA of this "marine alpha" cluster indicate that the group dominates bacterioplankton communities in estuarine and nearshore regions of the southeastern U.S. coast. Marine alpha bacteria decline predictably in abundance with decreasing salinity along estuarine transects and are not detectable in low-salinity (5‰) or freshwater samples. Sequences of 16S rDNA obtained from seawater by PCR with one group-specific oligonucleotide as a primer confirm that the oligonucleotide targets only members of this phylogenetic cluster. Likewise, sequences of 16S rDNA obtained from seawater by PCR with several different pairs of nonspecific primers show an unusually high abundance of marine alpha sequences (52 to 84%) among the clones, which possibly indicates a PCR bias toward the group. Members of the marine alpha group were readily cultured from coastal seawater, accounting for 40% of the colonies isolated on low-nutrient marine agar, based on hybridizations with the group-specific 16S rDNA probe and on sequence analysis. This is the first description of a numerically dominant cluster of coastal bacteria, identified by molecular techniques, that can be readily cultured and studied in the laboratory.

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A numerically important member of marine enrichment cultures prepared with lignin-rich, pulp mill emuent was isolated. This bacterium was gram negative and rod shaped, did not form spores, and was strictly aerobic. The surfaces of its cells were covered by blebs or vesicles and polysaccharide fibrils. Each cell also had a holdfast structure at one pole. The cells formed rosettes and aggregates. During growth in the presence of lignocellulose or cellulose particles, cells attached to the surfaces of the particles. The bacterium utilized a variety of monosaccharides, disaccharides, amino acids, and volatile fatty acids for growth. It hydrolyzed cellulose, and synthetic lignin preparations were partially solubilized and mineralized. As determined by 16s rRNA analysis, the isolate was a member of the (Y subclass of the phylum Proteobacteria and was related to the genus Roseobacter. A signature secondary structure of the 16s rRNA is proposed. The guanine-plus-cytosine content of the genomic DNA was 65.0 mol%. On the basis of the results of 16s rRNA sequence and phenotypic characterizations, the isolate was sufficiently different to consider it a member of a new genus. Thus, a novel genus and species, Sagittulu stelhta, are proposed; the type strain is E-37 (= ATCC 700073).Lignin degradation in salt marsh ecosystems is an important biogeochemical process due to the high primary productivity in such ecosystems and the abundance of vascular-plant-derived lignocellulosic material (4, 24). While both bacteria and fungi can be involved in the degradation of lignin (54), in aquatic environments bacteria are probably responsible for the utilization of the most refractory components (27,35). In a salt marsh, bacteria mediate most of the lignin degradation (5). Although members of at least one genus of bacteria known to be involved in lignin degradation in soils (the genus Streptomyces) have been identified in salt marsh sediments (37), little else is known about the identities of the bacterial lignin degraders in these systems. Thus, the isolation of lignolytic bacterial strains from salt marshes is significant from an ecological perspective. In addition, waste from the pulp and paper industry is another important source of polymeric and highly recalcitrant lignin in some coastal marine environments. Microbial communities are known to mineralize this waste in salt marsh ecosystems (33).In order to study the lignolytic potential of marine organisms, bacteria were isolated from a community growing in seawater with the high-molecular-weight fraction of pulp mill emuent as the sole carbon source. One isolate, strain E-37T, became a dominant member of this enrichment community and eventually contributed up to 32% of the community DNA (22). The phenotypic and phylogenetic characteristics of this isolate indicate that it belongs to a new genus of marine bacteria. In this paper we propose the name Sagittula stellata gen. nov., sp. nov., and designate strain E-37 the type strain of this species. MATERIALS AND METHODSIsolation. Strain ...

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Culturable bacteria that were numerically important members of a marine enrichment community were identified and characterized phylogenetically. Selective and nonselective isolation methods were used to obtain 133 culturable bacterial isolates from model marine communities enriched with the high-molecular-weight (lignin-rich) fraction of pulp mill effluent. The culture collection was screened against community DNA from the lignin enrichments by whole-genome hybridization methods, and three marine bacterial isolates were identified as being numerically important in the communities. One isolate was in the ␣-subclass of Proteobacteria, and the other two were in the ␥-subclass of Proteobacteria. Isolate-specific 16S rRNA oligonucleotide probes designed to precisely quantify the isolates in the lignin enrichment communities indicated contributions ranging from 2 to 32% of enrichment DNA, values nearly identical to those originally obtained by the simpler whole-genome hybridization method. Two 16S rRNA sequences closely related to that of one of the isolates, although not identical, were amplified via PCR from the seawater sample originally used to inoculate the enrichment medium. Partial sequences of 14 other isolates revealed significant phylogenetic diversity and unusual sequences among the culturable lignin enrichment bacteria, with the Proteobacteria, Cytophaga-Flavobacterium, and gram-positive groups represented.