Dual thermal ecotypes coexist within a nearly genetically identical population of the unicellular marine cyanobacterium Synechococcus.

The extent and ecological significance of intraspecific functional diversity within marine microbial populations is still poorly understood, and it remains unclear if such strain-level microdiversity will affect fitness and persistence in a rapidly changing ocean environment. In this study, we cultured 11 sympatric strains of the ubiquitous marine picocyanobacterium Synechococcus isolated from a Narragansett Bay (RI) phytoplankton community thermal selection experiment. Thermal performance curves revealed selection at cool and warm temperatures had subdivided the initial population into thermotypes with pronounced differences in maximum growth temperatures. Curiously, the genomes of all 11 isolates were almost identical (average nucleotide identities of >99.99%, with >99% of the genome aligning) and no differences in gene content or single nucleotide variants were associated with either cool or warm temperature phenotypes. Despite a very high level of genomic similarity, sequenced epigenomes for two strains showed differences in methylation on genes associated with photosynthesis. These corresponded to measured differences in photophysiology, suggesting a potential pathway for future mechanistic research into thermal microdiversity. Our study demonstrates that present-day marine microbial populations can harbor cryptic but environmentally relevant thermotypes which may increase their resilience to future rising temperatures.

Genome sequences of four agarolytic bacteria from the Bacteroidia and Gammaproteobacteria.

Here we present the genomes of four marine agarolytic bacteria belonging to the Bacteroidota and Proteobacteria. Two genomes are closed and two are in draft form, but all are at least 99% complete and offer new opportunities to study agar-degradation in marine bacteria.

A CURE for Physiological Characterization of Bacterioplankton in Liquid Culture.

Bacterial characterization is an important aspect of microbiology that includes experimentally determining growth rates, environmental conditions conducive to growth, and the types of energy sources microorganisms can use. Researchers use this information to help understand and predict an organism's ecological distribution and environmental functions. Microbiology students generally conduct bacterial characterization experiments in their coursework; however, they are frequently restricted to model organisms without ecological relevance and already well-studied physiologies. We present a course-based undergraduate research experience (CURE) curriculum to involve students in characterization of previously untested, ecologically relevant aquatic free-living bacteria (bacterioplankton) cultures to identify the usable nutrient substrates, as well as the temperature and salinity ranges conducive to growth. Students use these results to connect their organism's physiology to the isolation environment. This curriculum also exposes students to advanced microbiology methods such as flow cytometry for measuring cell concentrations, teaches them to use the programming language R for data plotting, and emphasizes scientific communication through writing, speaking, poster creation/presentation, and social media. This CURE is an attractive introduction to scientific research and was successfully tested with 187 students in three semesters at two different universities. Students generated reproducible growth data for multiple strains across these different deployments, demonstrating the utility of the curriculum for research support.

Draft Genome Sequence of Strain LSUCC0112, a Gulf of Mexico Representative of the Oligotrophic Marine Gammaproteobacteria.

Here, we present the draft genome sequence of strain LSUCC0112, a cultured representative from the Gulf of Mexico that is phylogenetically close to the OM182 clade within oligotrophic marine Gammaproteobacteria LSUCC0112 shows the potential for aerobic heterotrophy, glycogen synthesis, flagellar motility, and assimilatory sulfate reduction.