Marine microbes are responsible for processing and consuming ca. half of the organic carbon produced in the ocean. Their activities help control the rates and locations at which carbon is respired to CO2 and nutrients are regenerated: these tiny organisms exert major control over global-scale processing of carbon and nutrients in the ocean. Because these microbes are so small, they must cut their food into smaller pieces before they can consume it: their tools, which are the equivalent of knives, are extracellular enzymes. These enzymes are shaped to chop up specific types of organic matter. This project aimed to discover whether there are predictable patterns in the rates and types of microbial extracellular enzyme activities in the ocean, in other words, if the types and rates at which organic matter can made available to microbes follow a discernable pattern. Finding out whether there are patterns in enzyme activities is important because we currently lack information about important factors that control the rate and location at which organic matter is cycled in the ocean: thanks to new techniques and discoveries, we know much more about the identities of marine microbes and their distributions in different parts of the ocean, but comparatively little is known about how they make a living: what do they eat, where do they eat it, and why do they focus on specific food sources? In short, understanding carbon and nutrient cycling in the ocean requires better understanding of the eating habits of marine microbes. As part of this project, we have found that marine microbes do in fact show broad-scale patterns in enzyme activities: a wider range (broader spectrum) of substrates is hydrolyzed in nearshore compared to offshore locations, in surface waters compared to deep ocean waters, and in temperate surface waters compared to Arctic surface waters. In the Arctic, specific substrates are hydrolyzed at rates quite comparable to those measured in more temperate environments, but the Arctic microbial communities focus on fewer substrates (a narrower spectrum) than their temperate counterparts. These differences parallel differences in microbial community composition: Arctic microbial communities are compositionally quite different from more temperate microbial communities. We have also found that there are considerable differences in enzyme activities with depth: surface and subsurface microbial communities often show differences in the spectrum of substrates hydrolyzed, with a decreasing spectrum of substrates hydrolyzed at greater depth. Intriguingly, addition of high molecular weight (large) marine organic matter to a water sample from the open ocean can lead to changes in the spectrum of enzyme activities that is measured: numerically minor members of microbial communities become more dominant as a broader spectrum of enzyme activities is measured. Changes in the availability of specific foods that require enzymatic hydrolysis thus can tilt the balance in a microbial population, leading to dominance of previously minor members, due to their unique abilities with the required enzymatic tools. We also discovered by chance that many marine microbes carry out a previously unknown means of obtaining their food: in essence, they grab onto their substrates as if they were spaghetti noodles, chopping off pieces with extracellular enzymes but holding them firmly with binding proteins so that all of a substrate end up being taken up by a single cell (rather than many cells having the opportunity to take up chopped-off pieces of substrates.) This mechanism of substrate uptake (termed ?selfish?) was recently discovered among human gut bacteria, but was unknown in the marine environment. Observation of selfish behavior among a large fraction of microbes in the ocean helps explain patterns of substrate consumption that had previously been observed by other scientists. Carrying out this project required the participation of many people, including a large number of undergraduate students who participated in both lab and fieldwork. These undergraduates were mentored by the graduate students and scientists involved in the project. We also collaborated with scientists from Germany and Denmark, who funded expeditions on which we participated in the high Arctic, in Greenland, and in the Pacific Ocean. Results of this project have been incorporated in classes that the PI teaches. Moreover, one of our discoveries – of the selfish mechanism of enzymatic hydrolysis and substrate uptake – is due to the techniques we have developed to measure enzyme activities, in combination with the advanced microscopy capabilities of our collaborators at the Max Planck Institute for Marine Microbiology (in Bremen, Germany). This approach is now being applied also to examine substrate uptake among microorganisms of the human gut, an application that has medical and biomedical implications well beyond the scope of our initial research project. Last Modified: 11/05/2017 Submitted by: Carol Arnosti