Catalyzes the first glycosylation step in glycosphingolipid biosynthesis, the transfer of glucose to ceramide to produce glucosylceramides (GlcCer). GlcCer are known to contribute to the physical properties and physiological functions of membranes and may regulate signal transduction (PubMed:19240113, PubMed:21325339). Only branched-chain sphingoid bases like 15-methylhexadecasphing-4-enine are used for generating complex sphingolipids in Caenorhabditis elegans (PubMed:7651085). Together with cgt-3, plays a role in the trafficking of proteins such as mig-14 to the cell membrane in intestinal cells (PubMed:26115433). an N-acylsphing-4-enine + UDP-alpha-D-glucose = a beta-D-glucosyl-(1<->1')-N-acylsphing-4-enine + H(+) + UDP N-acyl-15-methylhexadecasphing-4-enine + UDP-alpha-D-glucose = H(+) + N-acyl-1-beta-D-glucosyl-15-methylhexadecasphing-4-enine + UDP Lipid metabolism; sphingolipid metabolism. Expressed in excretory canals, pharyngeal intestinal valve, intestine and intestinal rectal valve. The D1, D2, D3, (Q/R)XXRW motif is a critical part of the GCS active site, involved in catalysis and UDP-sugar binding. Knockdown of cgt-1 alone reduces brood size, while simultaneous knockdown of cgt-3 and cgt-1 results in a larval stage death (L1 lethal) phenotype (PubMed:19240113, PubMed:21325339). Double RNAi-mediated knockdown together with cgt-3 reduces the rate of development and restores the basolateral cell membrane localization of mig-14 in intestinal cells in a sgk-1 ok538 mutant background (PubMed:26115433). Belongs to the glycosyltransferase 2 family.