Acute toxicity of chlorpyrifos (CP) and its principal metabolite 3,5,6-trichloro-2-pyridinol (TCP) alone and in combination have been evaluated using a test battery comprising aquatic organisms from different trophic levels: luminescent marine bacteria Aliivibrio fischeri, freshwater unicellular alga Pseudokirchneriella subcapitata, and cladoceran Daphnia magna. As expected, D. magna was the more sensitive organism to the compounds tested, being CP more toxic than its metabolite. On the contrary, TCP was found to be more toxic than its parental compound to A. fischeri and P. subcapitata. In all cases, the mixture of CP and its metabolite was more toxic than the compounds tested separately, multiplying between 5 and 200 times CP toxicity level and up to 15 times TCP toxicity level. These results indicate that the co-existence of parent chemical and its degradation product in the environment can result in a synergic interaction involving high risk to the aquatic ecosystems. Graphical abstract

Chlorpyrifos (CP), a widely used pesticide, and its metabolite 3,5,6-trichloro-2-pyridinol (3,5,6-TCP), are xenobiotic compounds detected in many biomes, notably in marine sediments, all over the world. These compounds are posing a serious environmental and health problem given their toxicity to wildlife and possible exposure effects to human neurodevelopment. Microorganisms at CP-impacted environments could harbor metabolic capabilities that can be used as indicators of the biological effects of the contaminant and could encode selected functions reactive against contaminants. Those features could be used for microbial ecotoxicology applications by collectively using analytical, enzymatic, microbiological and toxicological techniques in order to assess the biological effects of pollutants and other environmental/climatic stressors in ecosystems. The objective of this study was to assess the variability in the metabolic responses of yeast isolates from CP-contaminated marine sediments as potential biological indicators for microbial ecotoxicology testing. Sediment samples from a South Caribbean tropical shore (Cartagena Bay, Colombia) were collected, and deoxyribonucleic acid (DNA) was recovered from lyophilized aliquots. The DGGE (Denaturing Gradient Gel Electrophoresis) technique targeting fungal Internal Transcribed Spacer (ITS) showed the great diversity of fungal types. Simultaneously, yeast strains were isolated from the freshly collected sediment samples. Physiological characterization including API 20C and antibiosis tests, growth patterns at salt concentrations (2/4/10/25%), temperatures (4/25/37/45 °C), esterase activity assay and resistance tests to CP/TCP toxicity resulted in 10 isolated yeast strains, identified as Candida spp. (6), Cryptococcus spp. (3). and Rhodotorula spp. (1), showing promising characteristics to be used as a test for yeast-based ecotoxicity indicators. The patterns of carbohydrate assimilation, low antibiosis, presence of esterases/lipases, growth in a wide range of temperatures and salt concentrations, and tolerance to minimal inhibitory concentrations of CP and TCP are factors useful for testing environmental samples.

Modern agriculture faces critical challenges from soil degradation and excessive use of chemical fertilizers, threatening sustainable seed germination and crop establishment. The main objective of this research was to evaluate the feasibility of using Pseudomonas spp. isolated from Colombian mangrove sediments as biofertilizers to enhance crop productivity, with an emphasis on Lactuca sativa (lettuce) seed-to-seedling transition. Fifty-eight isolates were characterized and screened for their ability to improve the germination of the lettuce seeds, but only nine strains showed promising activity. The strains were identified at the species level and screened for Plant growth-promoting rhizobacteria (PGPR) traits such as indole-3-acetic acid (IAA) production, phosphate solubilization, organic acid production, and salt tolerance (5%). Four different species were identified, namely Pseudomonas putida (one strain), Pseudomonas monteiilli (two strains), Pseudomonas taiwanensis (one strain), and Pseudomonas aeruginosa (four strains). P. aeruginosa strains P8 and P9 demonstrated exceptional performance, significantly improving root elongation, seedling biomass, and antioxidant activity compared with the uninoculated plants in vitro. These strains showed dual agrobiotechnological value: (i) enhancing early seedling vigor through hormonal stimulation and (ii) improving nutrient availability via phosphate solubilization. Our findings highlight the biotechnological potential of mangrove-associated Pseudomonas spp. as a sustainable alternative to chemical fertilizers, particularly for seed priming and seedling establishment systems in stress-prone soils.