Karen Caroline Ferreira Santaren

Marine environments are frequently impacted by petroleum‐derived hydrocarbons, which pose ecological risks because of their toxic, mutagenic, and carcinogenic potential. Microorganisms play a crucial role in hydrocarbon degradation, and understanding the influence of time and hydrocarbon type on microbial dynamics helps improve bioremediation strategies. In this study, marine water samples were used to assemble microcosms containing different hydrocarbon contaminants (naphthalene–NAF, crude oil–OL, and a synthetic mixture–MIX) and were incubated for 7, 15, 30, 45, and 60 days under controlled conditions. The bacterial community structure and composition were analyzed via 16S rRNA gene sequencing combined with functional prediction via PICRUSt2. Alpha diversity differed significantly among contaminants, with OL and MIX supporting more diverse communities. Beta diversity was shaped by both contaminant type and incubation time. Hydrocarbon‐degrading taxa such as Marinobacter , Alteromonas , Pseudomonas , and Thalassospira dominated at different stages, which was consistent with a functional progression from aliphatic oxidation (K00496) to successive steps of aromatic ring degradation (K00529, K00448, K07104). Together, these results demonstrate that hydrocarbon type and exposure time shape microbial succession, driving taxonomic differentiation and metabolic specialization, and providing insights for improving bioremediation strategies in marine environments.

Background: Poultry litter is the main waste of poultry farming and is widely used as an agricultural fertilizer. However, owing to the use of antimicrobials in animal production, it can accumulate antimicrobial residues, antimicrobial-resistant bacteria (ARB), and antimicrobial resistance genes (ARGs). This study aimed to evaluate the impact of poultry litter use on the microbiome and resistome of agricultural soils. Methods: Soil samples from fertilized and unfertilized plots were collected from two horticultural farms that intensively use poultry litter. Microbiome composition was assessed using 16S rRNA sequencing. A culture-dependent method was used to isolate resistant strains on CHROMagar plates supplemented with sulfamethoxazole or ciprofloxacin. ARGs and integrase-encoding genes were identified by PCR. Results: Microbiome analysis revealed significant differences in structure and composition between poultry litter-fertilized and unfertilized soils. Fertilized soils exhibited greater alpha diversity and richness. Bacillota, commonly found in the avian gastrointestinal tract, were more abundant in fertilized soils. A total of 62 resistant strains were isolated, and 23 clinically relevant strains harbored ARGs, including fluoroquinolone (qnrA and qnrB) and β-lactam (bla_GES, bla_TEM, and bla_SHV) resistance genes. Class 1 and 2 integron-associated genes (intI1 and intI2) were also detected. Notably, the rare bla_GES gene was detected in Bacillus sp. from unfertilized soil. Similarly, qnrA co-occurred with bla_SHV in a Bosea sp. strain from unfertilized soil. Conclusions: These findings highlight the potential for ARB dissemination in agricultural environments, where ARB and ARGs, once introduced into soils, may spread by weathering and other environmental factors, complicating negative control selection in in situ studies.