Alginate/albumin in incubation solution mediates the adhesion and biofilm formation of typical marine bacteria and algae

Guanidine-modified polysaccharide conditioning layer designed for regulating bacterial attachment behaviors

Biofouling has been persisting as a global problem due to the difficulties in finding efficient and environmentally friendly antifouling coatings for long-term applications. Initial attachment of bacteria on material surface and subsequent formation of biofilm are the predominate phenomena accounting for subsequent occurrence of biofouling. Among the various factors influencing the bacterial attachment, conditioning layer formed by organic macromolecules usually plays the key role in mediating bacterial attachment through altering physicochemical properties of substrate surface. In this study, a guanidine-modified polysaccharide conditioning layer with the capability of tuning the bacterial attachment is constructed and characterized. Dextran, a polysaccharide widespread in bacteria extracellular polymeric substances (EPS), is oxidized by sodium periodate, and cationic polymer polyhexamethylene guanidine hydrochloride (PHMG) is anchored to oxidized dextran (ODEX) by Schiff base reaction. AFM characterization reveals morphological changes of the polysaccharide conditioning layer from tangled chain to island conformation after the PHMG modification. The guanidine-based dextran conditioning layer promotes attachment of both P. aeruginosa and S. aureus and disrupted bacterial cytomembranes are seen for the attached bacteria due to electrostatic interaction of the electropositive guanidine group with the electronegative bacteria. The guanidine-based dextran conditioning layer shows a low survival ratio of 22 %-34 % and 1 %-4 % for P. aeruginosa and S. aureus respectively after incubation in the bacterial suspension for 72 hours. The results would give insight into further exploring the potential applications of the newly designed polysaccharides conditioning layer for combating occurrence of biofouling.

Enhanced antifouling properties of marine antimicrobial peptides by PEGylation

Covalent immobilisation of antimicrobial peptides (AMPs) on underwater surfaces to combat marine biofouling is of great interest as it is an efficient, broad-spectrum and environmentally friendly strategy. Similar to post-translational modifications of natural proteins, artificial modifications of antimicrobial peptides can introduce important impacts on their properties and functions. The present work revealed the enhanced effect of PEGylation on the antifouling properties of marine antimicrobial peptides (LWFYTMWH) through grafting the modified peptides on aluminium surfaces. PEG was coupled to the peptide by solid-phase peptide synthesis, and the PEGylated peptides were bioconjugated to the aluminium surfaces which was pre-treated by aryldiazonium salts to introduce carboxyl groups. The carboxy group has been activated through the reaction with 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide. The successful modification was confirmed via FT-IR and XPS. Interestingly, the PEGylated peptides modified surfaces could kill 90.0% Escherichia coli (Gram-negative) and 76.1% Bacillus sp. (Gram-positive), and showed better antifouling performance than the original peptides modified surfaces. Furthermore, molecular dynamics simulations showed PEGylation could enhance the ability of peptides to destroy membrane. The PEGylated peptides inserted into the membrane and induced the change in local curvature of membrane, leading to the rupture of membrane. The presence of PEG changed the antimicrobial peptides into more flexible conformations and the high hydrophilicity of PEG hindered the settlement of bacteria. These might be the two main working mechanisms for the increased antifouling efficiency of PEGylated peptides modified surface. This study provided a feasible modification strategy of antimicrobial peptides to enhance their antifouling properties.

Assess heavy metals-induced oxidative stress of microalgae by Electro-Raman combined technique

Oxidative stress of aquatic microorganisms under heavy metal stress is closely reflected by metabolite changes in cells but it is very difficult to study due to the fast metabolism process and severe in-situ measurements hurdle. Herein, the oxidative stress of cadmium on Euglena gracilis was systematically studied through multi-combined techniques. In particular, for the first time electrochemical approach was associated with Raman spectroscopy imaging to vividly to investigate temporal-spatially varied oxidative stress and its effects on cells metabolism, in which former real-time measured a volcanic relation of extracellular hydrogen peroxide versus the increase of cadmium stress, while the latter shows the corresponding metabolic changes by Raman imaging of single cells. This work builds a bridge to unravel the mechanism of cellular oxidative stress under harsh conditions in a more systematic and holistic approach, while holding a great promise to construct heavy metal biosensors precisely monitoring high heavy metal tolerance strains for environmental modification.