Production and characterisation of a marine Halomonas surface-active exopolymer

Tony Gutierrez, Gordon Morris, Dave Ellis, Barbara Mulloy, Michael D. Aitken

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Abstract

During screening for novel emulsifiers and surfactants, a marine gammaproteobacterium, Halomonas sp. MCTG39a, was isolated and selected for its production of an extracellular emulsifying agent, P39a. This polymer was produced by the new isolate during growth in a modified Zobell's 2216 medium amended with 1% glucose, and was extractable by cold ethanol precipitation. Chemical, chromatographic and nuclear magnetic resonance spectroscopic analysis confirmed P39a to be a high-molecular-weight (~ 261,000 g/mol) glycoprotein composed of carbohydrate (17.2%) and protein (36.4%). The polymer exhibited high emulsifying activities against a range of oil substrates that included straight-chain aliphatics, mono- and alkyl- aromatics and cycloparaffins. In general, higher emulsification values were measured under low (0.1 M PBS) compared to high (synthetic seawater) ionic strength conditions, indicating that low ionic strength is more favourable for emulsification by the P39a polymer. However, as observed with other bacterial emulsifying agents, the polymer emulsified some aromatic hydrocarbon species, as well as refined and crude oils, more effectively under high ionic strength conditions, which we posit could be due to steric adsorption to these substrates as may be conferred by the protein fraction of the polymer. Furthermore, the polymer effected a positive influence on the degradation of phenanthrene by other marine bacteria, such as the specialist PAH-degrader Polycyclovorans algicola. Collectively, based on the ability of this Halomonas high-molecular-weight glycoprotein to emulsify a range of pure hydrocarbon species, as well as refined and crude oils, it shows promise for the bioremediation of contaminated sites.

Original languageEnglish
Pages (from-to)1063-1076
Number of pages14
JournalApplied Microbiology and Biotechnology
Volume104
Issue number3
Early online date7 Dec 2019
DOIs
Publication statusPublished - Feb 2020

Keywords

  • Biodegradation
  • Exopolymers
  • Halomonas
  • Hydrocarbons
  • Marine environment

ASJC Scopus subject areas

  • Biotechnology
  • Applied Microbiology and Biotechnology

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