Cho, Jang-Cheon

AbstractBacteria of the SAR202 clade, within the phylum Chloroflexota, are ubiquitously distributed in the ocean but have not yet been cultivated in the lab. It has been proposed that ancient expansions of catabolic enzyme paralogs broadened the spectrum of organic compounds that SAR202 bacteria could oxidize, leading to transformations of the Earth’s carbon cycle. Here, we report the successful cultivation of SAR202 bacteria from surface seawater using dilution-to-extinction culturing. The growth of these strains is very slow (0.18–0.24 day−1) and is inhibited by exposure to light. The genomes, of ca. 3.08 Mbp, encode archaella (archaeal motility structures) and multiple sets of enzyme paralogs, including 80 genes coding for enolase superfamily enzymes and 44 genes encoding NAD(P)-dependent dehydrogenases. We propose that these enzyme paralogs participate in multiple parallel pathways for non-phosphorylative catabolism of sugars and sugar acids. Indeed, we demonstrate that SAR202 strains can utilize several substrates that are metabolized through the predicted pathways, such as sugars ʟ-fucose and ʟ-rhamnose, as well as their lactone and acid forms.

Although the familyHalieaceae(OM60/NOR5 clade) is an abundant and cosmopolitan clade widely found in coastal seas and involved in interactions with phytoplankton, a limited number of cultured isolates are available. In this study, we isolated six pure culturedHalieaceaestrains from coastal seawaters and performed a comparative physiological and genomic analysis to give insights into the phylogeny and metabolic potential of this family.

Significance Heme is essential for respiration. As a cofactor of cytochromes, heme functions as a main electron carrier in all respiratory electron transport chains. Therefore, it is natural to expect all respiring and free-living microorganisms to make heme. Against this expectation, here we show that the acI lineage, one of the most abundant bacterial groups in freshwater environments, is unable to biosynthesize heme and requires exogenous heme. Furthermore, we provide genomic evidence for putative heme auxotrophy among many not-yet-cultured aquatic microbial groups. Heme should be the focus of future research on the metabolic dependency among microorganisms and the role of exchangeable metabolites in structuring diverse ecosystems, and would also be a media component that must be considered when cultivating novel microbes.

Abstract The actinobacterial acI lineage is among the most successful and ubiquitous freshwater bacterioplankton found on all continents, often representing more than half of all microbial cells in the lacustrine environment and constituting multiple ecotypes. However, stably growing pure cultures of the acI lineage have not been established despite various cultivation efforts based on ecological and genomic studies on the lineage, which is in contrast to the ocean from which abundant microorganisms such as Prochlorococcus, Pelagibacter, and Nitrosopumilus have been isolated. Here, we report the first two pure cultures of the acI lineage successfully maintained by supplementing the growth media with catalase. Catalase was critical for stabilizing the growth of acI strains irrespective of the genomic presence of the catalase-peroxidase (katG) gene. The two strains, representing two novel species, displayed differential phenotypes and distinct preferences for reduced sulfurs and carbohydrates, some of which were difficult to predict based on genomic information. Our results suggest that culture of previously uncultured freshwater bacteria can be facilitated by a simple catalase-supplement method and indicate that genome-based metabolic prediction can be complemented by physiological analyses.

ABSTRACT We report the genome sequence of actinobacterial strain IMCC13023, isolated from arctic fjord seawater. Phylogenetic analysis of 16S rRNA gene showed that the strain is related to “ Candidatus Aquiluna rubra.” The genome information suggests that strain IMCC13023 is a photoheterotroph carrying actinorhodopsin, with the smallest genome ever reported for a free-living member of the Actinobacteria .

ABSTRACT The complete genome sequence of “ Candidatus Puniceispirillum marinum” IMCC1322, the first cultured representative of the SAR116 clade in the Alphaproteobacteria , is reported here. The genome contains genes for proteorhodopsin, aerobic-type carbon monoxide dehydrogenase, dimethylsulfoniopropionate demethylase, and C 1 compound metabolism. The genome information proposes the SAR116 group to be metabolic generalists in ocean nutrient cycling.

A Gram-negative, non-motile, chemoheterotrophic, facultatively aerobic, short-rod-shaped bacterium, designated IMCC1097T, was isolated from coastal seawater (10 m depth) of the East Sea, Korea. The temperature, pH and NaCl ranges for growth were 15–30 °C, pH 5.0–10.0 and 1.5–10 % NaCl. The colonies of the strain were very small, having a mean diameter of 0.05 mm. 16S rRNA gene sequence data indicated that the strain was most closely related to genera within the class Gammaproteobacteria. Members of the most closely related genera showed less than 90 % sequence similarity and included Saccharospirillum (89.3 %), Oleiphilus (88.7 %), Reinekea (88.2 %), Alcanivorax (86.4–87.6 %) and Zooshikella (87.6 %), which represent five different families of the order Oceanospirillales. Phylogenetic analyses showed that this marine strain represented a distinct phylogenetic lineage in the order Oceanospirillales and could not be assigned to any of the defined families in the order. The predominant fatty acids were C16 : 1 ω7c and/or iso-C15 : 0 2-OH, C18 : 1 ω7c and C10 : 0 3-OH, and the DNA G+C content was 57.9 mol%. These chemotaxonomic properties, together with phenotypic characteristics, served to differentiate the strain from phylogenetically closely related genera. The very low sequence similarities (<90 %) and distant relationships between IMCC1097T and members of the order Oceanospirillales suggested that the strain merited classification within a novel genus within a novel family in the order. On the basis of taxonomic evidence collected in this study, a novel genus and species are proposed, Litoricola lipolytica gen. nov., sp. nov., within a new family Litoricolaceae fam. nov. Strain IMCC1097T (=KCCM 42360T =NBRC 102074T) is the type strain of Litoricola lipolytica.

A Gram-negative, chemoheterotrophic, facultatively anaerobic coccus, designated IMCC1545T, was isolated from the digestive tract of a marine clamworm, Periserrula leucophryna, inhabiting a tidal flat of the Yellow Sea. Cells of strain IMCC1545T are non-motile, dividing by binary fission. The predominant fatty acids are anteiso-C15 : 0 and C18 : 0. The respiratory quinone is menaquinone-7 and the DNA G+C content is 52.1 mol%. Phylogenetic analyses based on 16S rRNA gene sequences using three treeing algorithms revealed that the strain formed a novel genus-level lineage within the phylum ‘Verrucomicrobia’. The most closely related named organisms to strain IMCC1545T are ‘Fucophilus fucoidanolyticus’ SI-1234 (86.5 % 16S rRNA gene sequence similarity), Alterococcus agarolyticus ADT3T (81.8 %) and Opitutus terrae PB90-1T (80.3 %), which belong to subdivision 4 of the ‘Verrucomicrobia’. Subdivision 4 of the ‘Verrucomicrobia’ (here named Opitutae classis nov.) was divided into two clades, a clade containing strain IMCC1545T and a clade containing Opitutus terrae. From the taxonomic data obtained in this study, it is proposed that the new marine isolate be placed into a novel genus and species named Puniceicoccus vermicola gen. nov., sp. nov. (the type strain of Puniceicoccus vermicola is IMCC1545T=KCCM 42343T=NBRC 101964T) within Puniceicoccaceae fam. nov and Puniceicoccales ord. nov in the class Opitutae. The family Opitutaceae fam. nov. and order Opitutales ord. nov. are also formally proposed.