Abstract
Traditional three-domain fungal and bacterial laccases have been extensively studied for their significance in various biotechnological applications. Growing molecular evidence points to a wide occurrence of more recently recognized two-domain laccase-like multicopper oxidase (LMCO) genes in
Streptomyces
spp. However, the current knowledge about their ecological role and distribution in natural or artificial ecosystems is insufficient. The aim of this study was to investigate the diversity and composition of
Streptomyces
two-domain LMCO genes in agricultural waste composting, which will contribute to the understanding of the ecological function of
Streptomyces
two-domain LMCOs with potential extracellular activity and ligninolytic capacity. A new specific PCR primer pair was designed to target the two conserved copper binding regions of
Streptomyces
two-domain LMCO genes. The obtained sequences mainly clustered with
Streptomyces coelicolor
,
Streptomyces violaceusniger
, and
Streptomyces griseus
. Gene libraries retrieved from six composting samples revealed high diversity and a rapid succession of
Streptomyces
two-domain LMCO genes during composting. The obtained sequence types cluster in 8 distinct clades, most of which are homologous with
Streptomyces
two-domain LMCO genes, but the sequences of clades III and VIII do not match with any reference sequence of known streptomycetes. Both lignocellulose degradation rates and phenol oxidase activity at pH 8.0 in the composting process were found to be positively associated with the abundance of
Streptomyces
two-domain LMCO genes. These observations provide important clues that
Streptomyces
two-domain LMCOs are potentially involved in bacterial extracellular phenol oxidase activities and lignocellulose breakdown during agricultural waste composting.