The Microbial Mechanisms of a Novel Photosensitive Material (Treated Rape Pollen) in Anti-Biofilm Process under Marine Environment

Abstract

Marine biofouling is a worldwide problem in coastal areas and affects the maritime industry primarily by attachment of fouling organisms to solid immersed surfaces. Biofilm formation by microbes is the main cause of biofouling. Currently, application of antibacterial materials is an important strategy for preventing bacterial colonization and biofilm formation. A natural three-dimensional carbon skeleton material, TRP (treated rape pollen), attracted our attention owing to its visible-light-driven photocatalytic disinfection property. Based on this, we hypothesized that TRP, which is eco-friendly, would show antifouling performance and could be used for marine antifouling. We then assessed its physiochemical characteristics, oxidant potential, and antifouling ability. The results showed that TRP had excellent photosensitivity and oxidant ability, as well as strong anti-bacterial colonization capability under light-driven conditions. Confocal laser scanning microscopy showed that TRP could disperse pre-established biofilms on stainless steel surfaces in natural seawater. The biodiversity and taxonomic composition of biofilms were significantly altered by TRP (p < 0.05). Moreover, metagenomics analysis showed that functional classes involved in the antioxidant system, environmental stress, glucose−lipid metabolism, and membrane-associated functions were changed after TRP exposure. Co-occurrence model analysis further revealed that TRP markedly increased the complexity of the biofilm microbial network under light irradiation. Taken together, these results demonstrate that TRP with light irradiation can inhibit bacterial colonization and prevent initial biofilm formation. Thus, TRP is a potential nature-based green material for marine antifouling.

Keywords: marine antifouling; microbial mechanisms; photosensitive material; rape pollen.

Figure 1

Characterization of TRP. (a) SEM images, (b) TEM images, (c) XRD pattern, (d) UV-vis DRS, (e) EDX characteristics, (f) hydroxyl radicals, and (g) superoxide radicals of TRP.

Figure 2

CLSM images of bacteria adhered to surfaces. Biofilms were simultaneously stained with propidium iodide (green) and SYTO^® 9 (red). The length and width of the 3-D box were both 118 µm, and the thickness was 25 µm.

Figure 3

Quantification of biofilm formation of natural surface (taking second week as an example) using COMSTAT software, including (a) bio-volume, (b) average thickness, and (c) roughness coefficient. Error bars indicate SD (n = 3). Different letters indicate a statistically significant difference (p < 0.05) among the various groups.

Figure 4

(a) Chao 1 index, (b) Shannon index, (c) Simpson index, and (d) NMDS based on the Bray–Curtis dissimilarities of bacterial communities. * p < 0.05, ** p < 0.01.

Figure 5

Relative abundance of different samples at (a) phylum and (b) genus levels, and (c) RDA of the correlations between bacterial community composition and environmental factors.

Figure 6

Network visualization of genus–genus interactions in (a) seawater group, (b) PL group, (c) P group, (d) L group, and (e) N group. Positive and negative correlations are shown in red and green, respectively. The nodes are colored according to different types of modularity classes. The size of each node is proportional to the node degree (Spearman’s |r| > 0.7, p < 0.05, top 50 most abundant genes).

Figure 7

Distribution of (a) major functional pathways (level 2) and (b) functional genes in four biofilms (data were standardized and centralized). * two-fold, ** four-fold, *** eight-fold.

Figure 8

Structural equation modeling (SEM) showing the linkage among environmental factors, genes, species diversity, network factors, and biofilm factors. Dotted arrows indicate non-significant paths (p > 0.05). Red and black arrows indicate positive and negative relationships, respectively. The path widths are scaled proportionally to the path coefficient. ** p < 0.01.

Figure 9

Culture and exposure of biofilm.

Figure 10

Schematic representation of mechanism of action.