Increasing aggregate size reduces single-cell organic carbon incorporation by hydrogel-embedded wetland microbes.

Microbial degradation of organic carbon in sediments is impacted by the availability of oxygen and substrates for growth. To better understand how particle size and redox zonation impact microbial organic carbon incorporation, techniques that maintain spatial information are necessary to quantify elemental cycling at the microscale. In this study, we produced hydrogel microspheres of various diameters (100, 250, and 500 μm) and inoculated them with an aerobic heterotrophic bacterium isolated from a freshwater wetland ( sp.

Single-cell isotope tracing reveals functional guilds of bacteria associated with the diatom Phaeodactylum tricornutum.

Bacterial remineralization of algal organic matter fuels algal growth but is rarely quantified. Consequently, we cannot currently predict whether some bacterial taxa may provide more remineralized nutrients to algae than others. Here, we quantified bacterial incorporation of algal-derived complex dissolved organic carbon and nitrogen and algal incorporation of remineralized carbon and nitrogen in fifteen bacterial co-cultures growing with the diatom Phaeodactylum tricornutum at the single-cell level using isotope tracing and nanoSIMS.

The V-type ATPase enhances photosynthesis in marine phytoplankton and further links phagocytosis to symbiogenesis.

Diatoms, dinoflagellates, and coccolithophores are dominant groups of marine eukaryotic phytoplankton that are collectively responsible for the majority of primary production in the ocean. These phytoplankton contain additional intracellular membranes around their chloroplasts, which are derived from ancestral engulfment of red microalgae by unicellular heterotrophic eukaryotes that led to secondary and tertiary endosymbiosis. However, the selectable evolutionary advantage of these membranes and the physiological significance for extant phytoplankton remain poorly understood.

Label-Free Multiphoton Imaging of Microbes in Root, Mineral, and Soil Matrices with Time-Gated Coherent Raman and Fluorescence Lifetime Imaging.

Imaging biogeochemical interactions in complex microbial systems─such as those at the soil-root interface─is crucial to studies of climate, agriculture, and environmental health but complicated by the three-dimensional (3D) juxtaposition of materials with a wide range of optical properties. We developed a label-free multiphoton nonlinear imaging approach to provide contrast and chemical information for soil microorganisms in roots and minerals with epi-illumination by simultaneously imaging two-photon excitation fluorescence (TPEF), coherent anti-Stokes Raman scattering (CARS), second-harmonic generation (SHG), and sum-frequency mixing (SFM). We used fluorescence lifetime imaging (FLIM) and time gating to correct CARS for the autofluorescence background native to soil particles and fungal hyphae (TG-CARS) using time-correlated single-photon counting (TCSPC).

Microbial community structure and function on sinking particles in the North Pacific Subtropical Gyre.

Sinking particles mediate the transport of carbon and energy to the deep-sea, yet the specific microbes associated with sedimenting particles in the ocean's interior remain largely uncharacterized. In this study, we used particle interceptor traps (PITs) to assess the nature of particle-associated microbial communities collected at a variety of depths in the North Pacific Subtropical Gyre. Comparative metagenomics was used to assess differences in microbial taxa and functional gene repertoires in PITs containing a preservative (poisoned traps) compared to preservative-free traps where growth was allowed to continue in situ (live traps).

High-resolution imaging of pelagic bacteria by Atomic Force Microscopy and implications for carbon cycling.

In microbial oceanography, cell size, volume and carbon (C) content of pelagic bacteria and archaea ('bacteria') are critical parameters in addressing the in situ physiology and functions of bacteria, and their role in the food web and C cycle. However, because of the diminutive size of most pelagic bacteria and errors caused by sample fixation and processing, an accurate measurement of the size and volume has been challenging. We used atomic force microscopy (AFM) to obtain high-resolution images of pelagic bacteria and Synechococcus.

Major role of microbes in carbon fluxes during Austral winter in the Southern Drake Passage.

Carbon cycling in Southern Ocean is a major issue in climate change, hence the need to understand the role of biota in the regulation of carbon fixation and cycling. Southern Ocean is a heterogeneous system, characterized by a strong seasonality, due to long dark winter. Yet, currently little is known about biogeochemical dynamics during this season, particularly in the deeper part of the ocean.