The twilight zone is an important depth of the ocean where particulate organic 
matter (POM) remineralization takes place, and prokaryotes contribute to 
more than 70% of the estimated remineralization. However, little is known 
about the microbial community and metabolic activity associated with 
different particles in the twilight zone. The composition and distribution of 
particle-attached prokaryotes in the twilight zone of the South China Sea 
(SCS) were investigated using high-throughput sequencing and quantitative 
PCR, together with the Biolog Ecoplate™ microplates culture to analyze 
the microbial metabolic activity. We  found that α- and γ-Proteobacteria 
dominating at the lower and upper boundary of the twilight zone, respectively; 
Methanosarcinales and Halobacteriales of the Euyarchaeota occupied in the 
larger particles at the upper boundary. Similar microbial community existed 
between euphotic layer and the upper boundary. Higher amount of shared 
Operational Taxonomic Units (OTUs) in the larger particles along the water 
depths, might be  due to the fast sinking and major contribution of carbon 
flux of the larger particles from the euphotic layer. In addition to polymers as 
the major carbon source, carbohydrates and amino acids were preferentially 
used by microbial community at the upper and lower boundary, respectively. 
This could potentially be attributed to the metabolic capabilities of attached 
microbial groups in different particles, and reflected the initial preference of 
the carbon source by the natural microbes in the twilight zone as well. The 
microbial structure and carbon metabolic profiles could be complemented with 
metatranscriptomic analysis in future studies to augment the understanding of 
the complex carbon cycling pathways in the twilight zone.