In the present study, a combined treatment strategy involving the addition of rhamnolipid, rhamnolipid-producing bacteria (Shewanella sp. BS4) and a native soil microbial community for the remediation of hydrocarbon-contaminated soil under pilot-scale conditions was adopted. The isolate BS4 (rhl+), demonstrating the highest emulsification activity and surface tension reduction efficiency, was identified based on 16 S rDNA sequencing as Shewanella sp. strain. Growth conditions for rhamnolipid production were optimized based on Central Composite Design (CCD) as 2.9% crude oil, a 54 × 10⁶ CFU g⁻¹ inoculation load of soil, a temperature of 30.5 °C, and a pH of 6.7. In situ bioremediation experiments, conducted using hydrocarbon-contaminated soil treated with the combination of rhamnolipid and rhamnolipid-producing bacteria, showed that the inoculated Shewanella sp. BS4, along with the indigenous soil microbial community, supported the highest hydrocarbon-degrading bacterial population and soil respiration activity, and this treatment resulted in 75.8% hydrocarbon removal efficiency, which was higher compared to contaminated soil devoid of any treatment.

Objectives A great setback in concern with public health is the development of emerging bacterial resistance towards conventional antibiotics making it a huge issue in the medical sector. To combat bacterial resistance, innovative strategies have been developed. One of the significant strategies is to target the bacterial pathogenicity through inhibition of quorum sensing (QS) mechanism among bacteria. QS is cell density dependent molecular communication prevailing in bacteria trends to express several genes conferring for its virulence, biofilm formation, antibiotic resistance, motility and plant-bacterial interactions etc. Methods: The current study investigates the anti-QS activity of red seaweed, against the targeted test pathogens Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter sp. and E. coli. Results and conclusion: At the concentration of 100 mg/mL of red seaweed extract, the biofilm was effectively reduced in Acinetobacter sp. and E. coli with 36 % and 40 % respectively. The exo polymeric substance (EPS) quantification from test pathogens in the presence of algal extract has declined to 40.8 % in Acinetobacter sp. and 14.8 % in E. coli reduction compared to S. aureus and K. pneumonia. Furthermore, the QS dependent motility activities are also reduced with the effect of algal extract. The efflux pump expression, being the noteworthy factor for antibiotic resistance has been inhibited by algal extract. The bioactive compounds from the algal extract A. fragilissima such as Melamine, Silicic acid, diethyl bis(trimethylsilyl) ester, Trimethyl [4-(1-methyl-1-methoxyethyl) phenoxy] silane, Benzo[h]quinoline, 2,4-dimethyl, Pyrazol-3(2H)-one, 4-nitro and 1,2-Bis(trimethylsilyl)benzene etc. Among them, Melamine showed high peak area and may responsible for the anti-QS activity and helps to overcome antibiotic resistance of the opportunistic pathogens. The QS dependent phenotypic expression among the test pathogens has been interrupted by the bioactive components of A. fragilissima.