Phylogenetic diversity of archaeal 16S rRNA and ammonia monooxygenase genes from tropical estuarine sediments on the central west coast of India

Phylogenetic diversity analyses of archaeal 16S rRNA and ammonia monooxygenase subunit A (AamoA) genes were carried out on sediment samples from the Mandovi and Zuari estuaries on the central west coast of India. The 16S rRNA gene libraries revealed quite high diversity of archaea in these sediments compared to previous reports from tropical and temperate estuarine sediments. Uncultured members of Crenarchaeota accounted for ∼78% of 433 archaeal 16S rRNA gene clones from both of the estuaries. We detected archaeal 16S and amoA gene-related organisms capable of ammonia oxidation. Among Crenarchaeota, marine group I (MG I) was the most predominant. Clones matching the uncultured methanobacteria were predominant among the ribogroups of Euryarchaeota. Our results indicate that archaeal diversity in tropical estuarine sediments is influenced by the mangrove vegetation bordering the lower stretches of both estuaries. Higher diversity may be related to elevated land drainage during the monsoon, particularly in the Mandovi estuary sediments. Also, the diversity of AamoA sequences was higher in Mandovi sediments than those from Zuari and other tropical and/or temperate estuaries studied previously.