UC San Diego

Marine bacterial influence on colloidal dissolved organic matter is a major driver in the biogeochemical cycling of carbon through the marine microbial loop. Interactions of individual bacteria with ambient colloids can affect nutrient availability and acquisition strategies, reshaping their immediate microenvironment. Direct observation of marine bacteria using atomic force microscopy (AFM) and complementary microscopies can yield insight and empirical evidence regarding mechanisms and effects of interactions of individual bacterial with colloidal particles from dissolved organic matter. The discovery of bacterial nanotubes in marine bacteria is reported with descriptive physical properties. Nanotube structures in Pseudoalteromonas sp. TW7 cells and Alteromonas sp. ALTSIO cell were determined to range between 200–600 nm in length and 50–160 nm in width. Individual connections were observed as hollow structures connecting bacterial cytoplasmic spaces. Particle aggregates, ranging 40–200 nm in width, were localized on marine bacteria surfaces, varying in size and quantity in a cell population, from interactions with E. coli ribosomes as model colloids. TW7 cells were observed with altered surface corrugation features and surface pits that can influence surface interaction with individual colloids. Corrugation features were determined to be 50–100 nm in size, and 20 nm deep. Hollow surface pits were measured to be 50–300 nm in width, and 10–50 nm in depth. A method using curvature radius analysis is proposed for analyzing AFM time-lapse image data of ALTSIO exposed to E. coli ribosomes to quantify particle attachment rates and coverage of cells. From observations, bacteria presented an average increase of 6.0 attached ribosomes when exposed to ribosome-amended seawater medium (approximate concentration of 8×1011 particles mL-1). In conclusion, bacterial nanotubes, surface particle clusters and surface pits are various cell features in bacterial interactions with organic colloid particles that are indicative of underlying mechanisms of bacterial transformation of dissolved organic matter throughout the global ocean.