Marine microbes are a large and diverse group, and are exposed to a wide variety of pressure, temperature, salinity, nutrient availability, and other environmental conditions [1–3]. They provide a huge potential source of novel enzymes with unique properties that may be useful in industry and biotechnology.
Lipolytic enzymes are ubiquitous in nature, and microbial lipolytic enzymes are commercially significant [4, 5]. In a classification scheme based on substrate preference, lipolytic enzymes are divided into lipases (EC 188.8.131.52) that hydrolyze long-chain acylglycerols ≥ 10 carbon chain), and esterases (EC 184.108.40.206) that hydrolyze short-chain acylglycerols ≤ 10 carbon chain). Both groups of biocatalysts have characteristics making them useful in a wide variety of industrial, pharmaceutical, biochemical, and biotechnological applications; e.g., they have high chemo-, region- and stereo-selectivity, stability in organic solvents, usually do not require cofactors, and do not catalyze side reactions [6, 7].
Lipolytic enzymes are serine hydrolases that share structural and functional characteristics such as an α/β hydrolase fold. Their catalytic mechanism involves a catalytic triad, or cofactor-independent activity . Based on comparisons of amino acid sequences and biological properties, prokaryote-derived lipolytic enzymes have been classified into eight families, termed true lipases (family I), the enzymes display a Gly-Asp-Ser-(Leu) [GDS(L)] motif containing the active-site Ser (GDSL, family II), family III, hormone-sensitive lipases (HSL, family IV), and families V~VIII .
A culture-independent approach, termed "metagenomics" [8, 9], allows screening for novel lipolytic enzymes, with industrial potential, from diverse environments . For example, genes encoding lipolytic enzymes have been isolated from metagenomic libraries constructed from environmental samples including forest soils [11, 12]; pond, lake, and river water [13–15] and hot spring and marine sediments [16, 17]. With only a few exceptions, characteristics of the novel enzymes found so far are not very appropriate for industrial applications. Thus, further metagenomics-based search for novel lipolytic enzymes from different sources, and with greater industrial applicability, is an important task.
The offshore marine environment of the northern South China Sea, near the southern China continental shelf and Hainan Island (Additional file 1, Table S1), contains nutrient-rich waters with concentrations of organic compounds and diversity of marine microbes greater than those of most other regions of the open ocean. We collected sediment samples from this area, and performed functional screening for novel lipolytic enzymes using a metagenomic library.