Understanding Biofilm Formation and Quorum Sensing in Marine Bacteria for Enhanced Utilization in Bioremediation

This thesis illustrates work on the characterization of marine bacterial biofilms and the role of quorum sensing [N-acyl homoserine lactone (AHL) autoinducer] in bioremediation technology. The involvement of quorum sensing genes (AHL synthase genes viz. lasI and rhlI) and exogenous AHLs on biofilm mediated degradation of polycyclic aromatic hydrocarbons (PAHs) was evaluated. Phenanthrene and pyrene were used as model organic compounds for bioremediation studies. Biofilm forming and PAHs utilizing marine bacteria were isolated from different marine environments. The potential isolates were characterized by 16S rRNA gene sequencing. The isolates were identified as Paenibacillus lautus NE3B01, Pseudomonas alcaliphila NE3B02, Alcaligenes faecalis NCW402, Stenotrophomonas acidaminiphila NCW702, Lysinibacillus fusiformis NCW903, P. mendocina NR802, Sporosarcina luteola NR402, P. pseudoalcaligenes NP103, Pseudomonas sp. NP202 and P. aeruginosa N6P6. Biofilm architecture was characterized by Scanning Electron Microscopy (SEM) and Confocal Laser Scanning Microscopy (CSLM). Maximum biofilm growth in terms of thickness was observed for P. aeruginosa N6P6 (66.76±4.11 μm) followed by P. pseudoalcaligenes NP103 (28.73±3.22 μm). Significant differences were observed in biofilm growth conditions, topological parameters and extracellular polymeric substances (EPS) among the isolates. With biofilm culture in 7 d, >70% phenanthrene degradation was observed in Stenotrophomonas acidaminiphila NCW702, P. mendocina NR802, P. aeruginosa N6P6 and P. pseudoalcaligenes NP103 biofilm. However, about 50% pyrene degradation was observed with P. aeruginosa N6P6 and P. pseudoalcaligenes NP103 biofilm. Apart from phenanthrene and pyrene, all the isolates were also able to grow on multiple aromatic compounds such as toluene, biphenyl, naphthalene and anthracene. PAHs degradation was also studied in a soil microcosm using marine bacterial consortium (named as NCPR composed of Stenotrophomonas acidaminiphila NCW702, Alcaligenes faecalis NCW402, P. mendocina NR802, P. aeruginosa N6P6 and P. pseudoalcaligenes NP103). A significant increase in PAHs degradation of soil was observed in presence of consortium NCPR