The comparative plastisphere microbial community profile at Kung Wiman beach unveils potential plastic-specific degrading microorganisms.

Background: Plastic waste is a global environmental issue that impacts the well-being of humans, animals, plants, and microorganisms. Microplastic contamination has been previously reported at Kung Wiman Beach, located in Chanthaburi province along with the Eastern Gulf of Thailand. Our research aimed to study the microbial population of the sand and plastisphere and isolate microorganisms with potential plastic degradation activity. Methods: Plastic and sand samples were collected from Kung Wiman Beach for microbial isolation on agar plates. The plastic samples were identified by Fourier-transform infrared spectroscopy. Plastic degradation properties were evaluated by observing the halo zone on mineral salts medium (MSM) supplemented with emulsified plastics, including polystyrene (PS), polylactic acid (PLA), polyvinyl chloride (PVC), and bis (2-hydroxyethyl) terephthalate (BHET). Bacteria and fungi were identified by analyzing nucleotide sequence analysis of the 16S rRNA and internal transcribed spacer (ITS) regions, respectively. 16S and ITS microbiomes analysis was conducted on the total DNA extracted from each sample to assess the microbial communities. Results: Of 16 plastic samples, five were identified as polypropylene (PP), four as polystyrene (PS), four as polyethylene terephthalate (PET), two as high-density polyethylene (HDPE), and one sample remained unidentified. Only 27 bacterial and 38 fungal isolates were found to have the ability to degrade PLA or BHET on MSM agar. However, none showed degradation capabilities for PS or PVC on MSM agar. Notably, Planococcus sp. PP5 showed the highest hydrolysis capacity of 1.64 ± 0.12. The 16S rRNA analysis revealed 13 bacterial genera, with seven showing plastic degradation abilities: Salipiger, Planococcus, Psychrobacter, Shewanella, Jonesia, Bacillus, and Kocuria. This study reports, for the first time of the BHET-degrading properties of the genera Planococcus and Jonesia. Additionally, The ITS analysis identified nine fungal genera, five of which demonstrated plastic degradation abilities: Aspergillus, Penicillium, Peacilomyces, Absidia, and Cochliobolus. Microbial community composition analysis and linear discriminant analysis effect size revealed certain dominant microbial groups in the plastic and sand samples that were absent under culture-dependent conditions. Furthermore, 16S and ITS amplicon microbiome analysis revealed microbial groups were significantly different in the plastic and sand samples collected. Conclusions: We reported on the microbial communities found on the plastisphere at Kung Wiman Beach and isolated and identified microbes with the capacity to degrade PLA and BHET.

Heavy metal bioaccumulation and risk assessment in fishery resources from the Gulf of Thailand.

The muscle tissues of 19 fish species, two crab species, and one shrimp species collected from the Gulf of Thailand (GoT) were analyzed to determine the levels of heavy metals, including Cu, Zn, Fe, Mn, Ni, Pb, Cd, and Hg. The results revealed that the mean concentrations of the heavy metals, in descending order, were Zn > Cu > Fe > Cd > Hg > Mn > Pb > Ni. Among the examined metals, zinc was found to be the most prevalent in fish tissues. Based on the risk assessment indices, the estimated average daily doses (ADD) of the heavy metals were found to be below the provisional tolerable daily intake (PTDI) recommended by the joint Committee of the Food and Agriculture Organization (FAO) and the World Health Organization (WHO) on food contaminants. The results of the target cancer risk analysis revealed no related cancer risk from the consumption of the fishes considered for the study. However, the target hazard quotient (THQ) values exceeded the threshold of 1 (THQ > 1) specifically for mercury in Gymnothorax spp. and Terapon spp. Furthermore, the calculated hazard index (HI) values for fish muscles were all below 1, indicating that there is no significant health risk for humans at the current consumption rates, except in Terapon species for both normal and habitual consumers. Notably, habitual consumers of Gymnothorax species showed the highest HI value (>1), suggesting potential long-term effects on human health when consuming larger quantities of these fishes.

Abundance, composition, and fate of microplastics in water, sediment, and shellfish in the Tapi-Phumduang River system and Bandon Bay, Thailand.

Microplastic contamination in the environment is a global problem, as evidenced by the increasing amount of research worldwide. To our knowledge, this study is the first to investigate the microplastic distribution in Bandon Bay, one of the most important maricultural areas of Thailand. Water and sediment samples from the Tapi-Phumduang River system (n = 10) and Bandon Bay (n = 5) were collected. Water sampling at the river mouth was carried out during a complete tidal cycle to estimate the microplastic flux to the bay during the wet season. Moreover, two commercial bivalve species grown in the bay, the green mussel (Perna viridis) and lyrate Asiatic hard clam (Meretrix lyrata), were analyzed. More items of microplastics were found in the river system than in the bay. During the tide cycle, one-third of the microplastics entering the bay were washed back upstream during high tide. This backflow consisted mainly of larger microplastics. The average daily load of microplastics to the bay was 22.4 × 109 items day-1. The load during low tide was approximately 4-5 times higher than that during high tide. The overall accumulation of microplastics in the bottom sediments of the river and in the bay was similar (p < 0.05). Green mussels showed significantly higher contamination with microplastics than clams. Notably, the small-sized shellfish contained more particles (items/g) than the large ones (p < 0.05). Fibers were detected in virtually all samples: water (98%), sediment (94%), mussels (100%), and clams (95%). Among these, microfibers (<1 mm) were detected in water (71%), sediment (63%), green mussels (63%), and clams (52%). Blue and white particles were the two most frequently observed colors, while the most dominant polymers were rayon, followed by polypropylene (PP) or polyethylene (PE), polyethylene terephthalate (PET), and nylon. To this end, we posit that river discharge was a significant source of microplastics in Bandon Bay, with minor additional contributions from fishing and mariculture activities within the bay. Ultimately, these microplastics may end up in the sediments and living organisms.

Effects of crude oil and aromatic compounds on growth and bioluminescence of Vibrio campbellii FS5.

Fifteen native luminescent bacteria were isolated from the Gulf of Thailand, and their sensitivity for the detection of toxicity of crude oil and its aromatic components was investigated. Of these isolates, Vibrio campbellii strain FS5 was one of the two most highly inhibited bacteria at all crude oil concentrations. This bacterium showed a decrease in luminescence intensity of between 10.7 and 80.2% after a 15-min exposure to 0.0001-10 mg/L of crude oil. The degree of bioluminescence inhibition increased with increasing concentrations of crude oil. The presence of crude oil at all concentrations had negative effects on the log bioluminescence per log number of viable cells after 15- to 105-min exposure. About 10 to 100 times, lower half maximal effective concentration (EC50) values were observed for polycyclic aromatic hydrocarbons (PAHs) than those for benzene, toluene, ethylbenzene, and xylene (BTEX). In the presence of each individual BTEX and PAH, the bioluminescence inhibition increased with increasing exposure time (1-32 h). This indigenous bacterium can be used as a simple and general indicator of oil contamination and its impact on coastal waters as well as for assessing potential toxicity during oil bioremediation.