Project description:Microbial photoautotroph-heterotroph interactions underlie marine food webs and shape ecosystem diversity and structure in upper ocean environments. However, the high complexity of in situ ecosystems renders it difficult to study these interactions. Two-member co-culture systems of picocyanobacteria and single heterotrophic bacterial strains have been thoroughly investigated. However, in situ interactions comprise far more diverse heterotrophic bacterial associations with single photoautotrophic organisms. Here, bacterial community composition, lifestyle preference, and genomic- and proteomic-level metabolic characteristics were investigated for an open ocean Synechococcus ecotype and its associated heterotrophs over 91 days of co-cultivation. The associated heterotrophic bacterial assembly mostly constituted five classes including Flavobacteria, Bacteroidetes, Phycisphaerae, Gammaproteobacteria, and Alphaproteobacteria. The seven most abundant taxa/genera comprised >90% of the total heterotrophic bacterial community, and five of these displayed distinct lifestyle preferences (free-living or attached) and responses to Synechococcus growth phases. Six high-quality genomes from the co-culture system were reconstructed inclusive of Synechococcus and the five dominant heterotrophic bacterial populations. The only primary producer of the co-culture system, Synechococcus, displayed metabolic processes primarily involved in inorganic nutrient uptake, photosynthesis, and organic matter biosynthesis and release. Two of the flavobacterial populations, Muricauda and Winogradskyella, and an SM1A02 population, displayed preferences for initial degradation of complex compounds and biopolymers, as evinced by high abundances of TBDT, glycoside hydrolase, and peptidases proteins. In contrast, the alphaproteobacterium Oricola sp. population mainly utilized low molecular weight DOM, including Flavobacteria metabolism byproducts, through ABC, TRAP, and TTT transport systems. Polysaccharide-utilization loci present in the flavobacterial genomes encoded similar trans-membrane protein complexes as Sus/cellulosome and may influence their lifestyle preferences and close associations with phytoplankton. The heterotrophic bacterial populations exhibited complementary mechanisms for degrading Synechococcus-derived organic matter and driving nutrient cycling. In addition to nutrient exchange, removal of reactive oxygen species and vitamin trafficking also contributed to the maintenance of the Synechococcus / heterotroph co-culture system and the interactions shaping the system.
Project description:Picocyanobacteria from the genus Synechococcus are ubiquitous in ocean waters. Their phylogenetic and genomic diversity suggests ecological niche differentiation, but the selective forces influencing this are not well defined. Marine picocyanobacteria are sensitive to Cu toxicity, so adaptations to this stress could represent a selective force within, and between, “species” also known as clades. We compared Cu stress responses in cultures and natural populations of marine Synechococcus from two co-occurring major mesotrophic clades (I and IV). Using custom microarrays and proteomics to characterize expression responses to Cu in the lab and field, we found evidence for a general stress regulon in marine Synechococcus. However, the two clades also exhibited distinct responses to copper. The Clade I representative induced expression of genomic island genes in cultures and Southern California Bight populations, while the Clade IV representative downregulated Fe-limitation proteins. Copper incubation experiments suggest that Clade IV populations may harbor stress-tolerant subgroups, and thus fitness tradeoffs may govern Cu-tolerant strain distributions. This work demonstrates that Synechococcus has distinct adaptive strategies to deal with Cu toxicity at both the clade and subclade level, implying that metal toxicity and stress response adaptations represent an important selective force for influencing diversity within marine Synechococcus populations.
Project description:Total bacterial DNA was isolated from water and sediment samples from a local watershed and 16S rRNA sequences were analyzed using the Illumina MiSeq v3 platform in order to generate snapshots of bacterial community profiles.
Project description:In this study, we explored the use of BONCAT in Synechococcus sp. – a globally important cyanobacteria. We characterized the growth and microscopically quantified HPG uptake under a range of HPG concentrations in marine Synechococcus sp. Further, we examined changes in protein expression of Synechococcus sp. grown under normal and nitrate-stressed conditions relative to a non-HPG control.
Project description:Total bacterial DNA was isolated from water and sediment samples from a local watershed and 16S rRNA sequences were analyzed using the Illumina MiSeq v3 platform in order to generate snapshots of bacterial community profiles. A total of 56 samples were collected that represent water and sediment samples from 14 sample sites over two different time points (November 18 and 25, 2011).