Marine resources such as marine invertebrates and mangrove plants favor the production of secondary metabolites that exhibit antifouling properties. These natural-derived compounds are considered environmentally friendly compared to synthetic compounds with similar activity and technological applications. The current study was conducted to determine the antifouling properties of Diadema setosum (DS) and Sonneratia lanceolata (SL) crude extracts and their incorporated paints, in addition to the identification of the metabolites involved. Both crude extracts were tested against Pseudomonas aeruginosa via a crystal violet assay, while the incorporated paints with 5% (SL5% and DS5%) and 10% (SL10% and DS10%) weight per volume (w/v) were tested in an aquarium and submerged in the seawater at Kemaman and Pulau Redang (Malaysia) for field testing. The identification of the bioactive compounds from the crude extracts was carried out using Liquid Chromatography-Mass Spectrometry (LC-MS). The results of the crystal violet assay showed that both of the crude extracts reduced the biofilm formed by Pseudomonas aeruginosa. The marine bacteria growths contained in natural seawater were inhibited the most by SL5%, followed by DS5%, DS10%, and SL10% in the aquarium testing. Based on the photographic observation, all of the paints incorporated with the crude extracts successfully reduced the settlement of fouling organisms compared to the blank paint, as lesser macroalgae were found growing on the SL5%, DS5%, and DS10%. The LC-MS results showed 3-Methyloxiranyl phosphonic acid; (2RS,3SR)-form from the SL crude extract, while the 8-Decene-1,3,5-triol, 3-Hydroxyundecanoic acid, and 1-O-(6-Deoxy-6-sulfoglucopyranosyl)glycerol; α-D-form, 3-Hexadecanoyl from the DS crude extract were involved in the antifouling properties. In conclusion, both crude extracts have the potential to be developed as antifouling agents.

Biofouling is defined as the excessive colonization process of epibiotic organisms, ranging from microfoulers to macrofoulers, on any submerged surface in water. Previous research has attempted to explore the antifouling activity of bacterial isolates due to the biofouling problems occurring worldwide. One solution is to inhibit the early stage of fouling using secondary metabolites produced by marine bacteria. This study aims to determine the antifouling activities of the marine microorganism P. aeruginosa and to characterize the bacteria isolated as a potential anti-biofouling agent. The bacterial isolate was cultured and isolated on a media culture. The bacteria culture extract was extracted using ethyl acetate and concentrated prior to the bioassay method. It was screened for antibacterial activities against Gram-positive and Gram-negative bacteria, such as Bacillus cereus, Streptococcus uberis, Pseudomonas sp., and Vibrio parahaemolyticus, using the disk diffusion technique. The extract was investigated to verify its bioactivity in the prevention of biofilm formation following the crystal violet assay and aquarium test. The results indicated the inhibition of activity through biofilm formation, with the highest percentage at 83% of biofilm inhibition at a concentration of 0.1563 mg/mL. The bacterial isolate at a concentration of 5% showed the highest reduction in bacteria colonies in the aquarium test (161.8 × 10³ CFU/mL compared to 722.5 × 10³ CFU/mL for the blank sample). The bacterial isolate was characterized through phenotypic and genotypic tests for species identification. It was identified as a Gram-stain-negative, aerobic, and long-rod-shaped bacteria, designated as RLimb. Based on the 16S rDNA gene sequencing analysis, RLimb was identified as Pseudomonas aeruginosa (accession number: OP522351), exhibiting a similarity of 100% to the described neighbor P. aeruginosa strain DSM 50071. These results indicated that these isolated bacteria can potentially be used as a substitute for toxic antifoulants to prevent the formation of microfoulers.

Methylene blue is one of the textile dyes that are commonly used in the textile coloring industry. The discharge of textile wastewater containing residual textile coloring substances into the environment can lead to environmental pollution. Thus, bioremediation can be a solution to reduce dye pollution by using bacterial strains. In the present study, two bacterial strains with the ability to degrade methylene blue dye were isolated from contaminated soil. Both isolated bacteria were further evaluated for the dye decolorization percentage and the effect of abiotic parameters on bacterial growth. The isolated bacteria were incubated in a mineral salt medium added with methylene blue dye for eight days in static aerobic conditions. The dye degradation was examined by using UV-VIS spectrophotometer at 665 nm. The isolated bacteria were identified as Klebsiella pneumoniae strain UMTFA1 (EK) and Pseudomonas aeruginosa strain UMTFA2 (EP) using 16s rRNA sequencing. The biodegradation study showed that Klebsiella pneumoniae strain UMTFA1 (EK) and Pseudomonas aeruginosa strain UMTFA2 (EP) were capable to degrade 10.52% and 11.65% of methylene blue dye after 8 days of incubation, respectively. The present study may provide a basis for biotreatment and bioremediation of dye-contaminated soils.

Biological treatment for textile wastewater always has a limitation in term of time of reaction and uncertainty along the process. This study focused on the decolorization of synthetic azo dyes in batch reactors with controlled thermotolerant anaerobic conditions. Less-volatile digested sludge collected from a palm oil biogas reactor was used as the organic biodegradation agent for azo dyes. Digested sludge contains high amounts of microbes with uncertain species viable for decolorization purposes. Sodium acetate trihydrate (C2H9NaO5) was used as carbon source and mixed with a specific composition of minimum salt media (MSM) in batch reactors as an additional nutrient. Digested sludge both in mesophilic (35°C) and thermophilic (55°C) conditions were found to be capable of decolorizing 100, 200 and 300 ppm of three types of azo dyes: Reactive Green 19 (45.56%, 69.73%; 63%, 73.49%; 70.02%, 75.92%), Reactive Orange 16 (46.08%, 78.4%; 64.21%, 85.52%; 74.95%, 85.91%) and Reactive Red 120 (29.11%, 85.32%; 63.35%, 87.69%; 72.02%, 89.5%) respectively after 7 days incubation time. Statistical analysis also showed that the anaerobic thermophilic conditions had significantly accelerated the decolorization process. The anaerobic thermophilic environment will be a good factor to include in future textile wastewater treatment plants.