Cell surface and cellular debris-associated heat-stable lipolytic enzyme activities of the marine alga Nannochloropsis oceanica

Abstract

Microbial surface display of lipases can be effectively employed for the development of whole-cell biocatalysts for industrial bioconversions. In the present work, we report for the first time the presence of thermostable lipolytic enzyme activities against p-nitrophenyl laurate, both on the cell surface and the cellular debris fraction of the marine microalga Nannochloropsis oceanica (strain CCMP1779). Whole cell-associated lipolytic activity (WCLA) shows a 2.5-fold stimulation after heat treatment at 100 °C for 60 min, while the activity of the respective cell debris is retained for 15 min. In contrast, heat treatment renders the soluble fraction of the disrupted cells inactive. The progress curve of cellular debris-associated lipase activity is biphasic and levels off very fast. Treatment with the surfactants SDS, Triton X-100 and CHAPS, which are known to inhibit lipase activity in various degrees, results in a loss of both cell bound and cell debris lipolytic activities (CDLA). The highest whole cell lipase catalytic efficiency was observed against p-nitrophenyl butyrate and the optimum pH for hydrolysis was determined at pH 7.0. Both unheated and heated undisrupted whole cell biocatalysts are also catalytically active against olive oil. High-salt concentrations (1M NaCl) lead to about 50% whole cell enzyme inhibition whereas the activity of heated cells increases. These findings offer novel insight into the biocatalytic properties and the biotechnological applicability of microalgal lipases from N. oceanica.