Glycoside hydrolases (also called glycosidases) are extremely common enzymes with roles in nature including degradation of biomass,in anti-bacterial defense strategies,in pathogenesis mechanisms and in normal cellular function.Metagenomics has emerged as an alternative approach to conventional microbial screening that allows exhaustive screening of microbial genomes in their natural environments.However,searching for desired traits from metagenomes is often problematic because of the lack of ultrahigh-throughput and cost-effective screening approaches.To address these circumstances,this work aims to establish a general ultrahigh-throughput screening platform using droplet-based microfluidics.We choose chitinase as a model of glycosidase for screening from metagenomes of deep-sea microbial communities.Single E.coli cell from metagenomic libraries and the fluorogenic substrate of chitinase were co-encapsulated into aqueous picoliter-volume droplets,dispersed in inert carrier oil and then incubated on the same chip.After incubation,the genes transformed into E.coli cells were expressed and the droplets containing active chitinases were sorted based on their own fluorescent intensities.Finally,the functional genes were recovered from the collected droplets.The droplet-screening frequency is in the range of hundreds to thousands of droplets per second.Compared to screening using microtiter plate-based systems,the volume and cost of the reagents are reduced by almost 104~105-fold,allowing the screening of 106~107 genes using only microliter-scale reagents.Meanwhile,we demonstrated the rapid exoglycosidase digestion of oligosaccharides employing microfluidic droplets to simplify the procedure of conventional oligosaccharide sequencing by the combination of enzymatic digestion and matrix-assisted laser desportion/ionization mass spectrometry (MALDI-MS),which requires repeated isolation and wastes much more time and efforts.When using microdroplets technology,the mixture for digestion reaction is compartmentalized into aqueous picoliter-volume droplets,dispersed in inert carrier oil.Each droplet is an enzymatic reaction vesssel with highly efficient hydrolysis (~37℃) due to rap uniformity of droplet size and temperature.After enzymatic digestion,the products are recovered and characterized by MALDI-MS.By performing microfluidic droplet-based reaction,the time required for glycosidase digestion could be shortened to several hours,which is very important for oligosaccharides sequencing and analysis.