Diversity distribution and functional characterization of bacteria from the mangrove sediments of northern Kerala India

Abstract

Mangrove ecosystems are productive coastal habitats supporting diversemicrobial communities. This study examined the influence of sediment characteristicson bacterial population and diversity. The hydrolytic enzyme potential andbioremediation capacity of the bacterial isolates obtained from the mangrovesediments of eight different stations in northern Kerala, i.e., Kasaragod, Edat,Valapattanam, Pazhayangadi, Kadalundi, Elathur, Ponnani and Chettuva, weredetermined. Sediment parameters varied across locations, with temperature rangingfrom 21–32°C, pH 6–7, salinity 3–38 ppt, organic matter 0.2 ± 0.03 to 7 ± 0.04%,carbohydrate 0.01 ± 0.002 to 0.25 ± 0.02 mg/g, protein 0.1 ± 0.02 to 9.9 ± 0.04 mg/g,lipid 0.2 ± 0.01 to 9.3 ± 0.02 mg/g, sand 46 to 97%, silt 0.3 to 55% and clay 0.3 to35%. Bacterial population ranged from 6 ± 0.03 to 8 ± 0.04 log10 CFU/10 g andcorrelated with organic matter, lipid and protein content of the sediment. A total of 708bacterial isolates representing 17 genera were identified, while metagenomic analysisrevealed 45 phyla and 1834 species. Genes associated with antibiotic synthesis,degradation of xenobiotic compounds and different bacteria involved in sulphur,nitrogen, iron and methane cycles were identified. Enzyme screening revealedhydrolytic potential for lipase producers (69%), followed by protease (55%), amylase(48%), cellulase (43%), DNase (27%), chitinase (3.5%), ligninase (3%) and laccase(1%). Based on enzyme potential, 35 isolates were identified using molecular methods.Eight strains (Enterobacter cloacae, E. asburiae, Serratia marcescens and Klebsiellaaerogenes) were selected for consortia development based on the extent ofextracellular enzyme production. Growth optimization was done for varying pH,temperature, salinity and agitation. Non haemolytic and compatible strains with similargrowth requirements were used to develop five consortia (CS01–CS05).Immobilization of the strains and consortia was done. Quantitative enzyme assaysshowed enhanced activity in immobilized consortia compared to free forms, except forlipase. The maximum enzyme activity in immobilized consortia was obtained foramylase (373 U/ml), ligninase (270 U/ml), cellulase (178 U/ml), lipase (63 U/ml),protease (32 U/ml), and chitinase (24 U/ml). Strain FST06 exhibited the highest lipaseactivity (64 U/ml). Biodegradation studies using sanitary napkins and polycoated carrybags demonstrated 29% and 8% degradation by free and immobilized consortia,respectively. The study highlights the rich bacterial diversity and metabolic potential ofKerala’s mangrove sediments, emphasizing their ecological importance and potentialfor application in bioremediation.