Interactions of algal spores and diatoms with mixed synthetic peptide SAMs

1000 1200 1400 1600 1800 Wavenumber (cm-1₎

Interactions of algal spores and diatoms

with mixed synthetic peptide SAMs.

Mixed peptide SAMs

The problem – marine biofouling

Biological tests

A synthetic cationic arginine-rich peptide is used to form mixed SAMs on gold substrates (via a thiol linker), with a shorter spacer molecule. IRAS, wetting and ellipsometry data demonstrate that the peptides form organised monolayers. Marine biofouling incurs additional costs and

environmental impact on the operation of vessels, heat exchangers, fishing equipment, desalination plants and many other facilities, by reduced efficency and increased fuel consumption. There are about 2500 fouling marine organisms, using a broad range of settlement strategies and bioadhesives. We study the interactions between surfaces and marine organisms in terms of physicochemical cues, in order to understand settlement behaviour and ultimately to improve anti-fouling properties of surfaces.

We have studied the attachment of a major ship fouling alga (Ulva) and a diatom (Navicula) to the mixed peptide SAMs.

H2N H N N H H N N H H N N H H N N H H N N H O O O O O O O O O O O HS HO HO HO HN H2N NH HN H2N NH HN H2N NH HN H2N NH ArgTyr

Normally settled (A) and ‘stuck’ (B) spores, with flagella still attached.

Ulva linza Navicula perminuta

Plant Spores

Ulva plants release spores which swim with the aid of flagella. As a suitable surface for settlement is located, a physiological change into a plant is started. Ulva spores lack cell walls, and expose the plasma membrane to the environment, while the

Navicula cells are encased within a silica cell wall.

The peptide SAMs were incubated in Ulva spores or Navicula cells for 1 h, whereupon the density of settled (attached) cells was determined.

Thiol ”anchor”

Up to 20 µM, free ArgTyr peptides in solution stimulate the settlement of Ulva spores. Above 20µM, spores lysed (died). No such effects were observed for the free amino acids of which the ArgTyr peptide is composed.

M. E. Pettitt, M. E. Callow, J. A. Callow

The University of Birmingham, School of Biosciences, Birmingham B15 2TT, UK

T. Ederth*, P. Nygren, T. Ekblad,

M. Östblom, B. Liedberg

Division of Molecular Physics, Department of Physics, chemistry and biology, Linköpings Universitet, SE-581 83 Linköping, Sweden, * ted@ifm.liu.se

H2N H N N H H N N H O O O O O HS Gly3spacer

FTIR data for mixed ArgTyr/spacer SAMs. Peak areas within the shaded region were used to estimate the surface fraction of the ArgTyr peptide for different solution fractions (right).

Contact angles (θθθθ_a) Thickness (Å) Mol-% ArgTyr 100% 75% 50% 20% 5% 0% 44° 26.2 52° 23.3 51° 21.5 47° 16.8 46° 16.5 41° 13.1 ( θ ( θ( θ

( θr < 10 for all mixtures )

Advanced nanostructured surfaces for the control of biofouling http://www.ambio.bham.ac.uk/

The density of settled Ulva spores increases with bound ArgTyr content but many of the 'settled' spores retained their flagella indicating that they had not gone through the normal settlement process; these spores probably died. Navicula cells, however,

are unaffected by the presence of the ArgTyr peptide; cell

attachment is not altered and no cells died.This difference is

probably due to the diatom cell wall preventing the bound ArgTyr peptide from contacting the plasma membrane.

Settlement results

Incubation assay

Summary:

The ArgTyr peptide interacts specifically with

Ulva

cell membranes, promoting adhesion to a surface,

but also preventing it from going through its normal settlement physiology, and ultimately causing cell death.

5 µm 0 50 100 150 200 250 300 0 5 20 50 75 100

Mol-% ArgTyr on surface

S p o re s p e r m m

2 Total Ulva spores

With flagella Dead spores 0% 5% 20% 50% 100% 75% Solution Mol-% ArgTyr 0 0.2 0.4 0.6 0.8 1 0 20 40 60 80 100 % ArgTyr in solution A b s o rb a n c e N o rm a li z e d p e a k a re a