Mangroves: A hotspot for novel bacterial and archaeal diversity

Mangrove ecosystems are highly productive ecosystems that harbor diverse microbial lineage playing multiple roles in nutrient cycling. Though several novel mangrove rhizospheres associated with bacterial genera and species have been reported from these unexplored wetland ecosystems, but yet to be studied for their richness and diversity including actinobacterial and archaeal communities. Therefore, this study was undertaken to decode the bacterial and archaeal communities associated with the rhizosphere regions of true mangrove speciesAvicennia marina and Rhizophora mucronata and their intersecting regions; and associated halophytic species -Suaeda maritima, and Salicornia brachiata of Pichavaram mangroves, Tamil Nadu, India. Amplified ribosomal DNA restriction analysis (ARDRA) and PCR denaturing gradient gel electrophoresis (PCR-DGGE) analysis techniques were adopted. About 567 culturable bacterial isolates with distinct morphology were purified, and nearly 88 distinct Operational Taxonomic Units (OTUs) were identified by ARDRA analysis. Phylogenetic analysis of representative groups indicated that the majority of the isolates belonged to Firmicutes (10 genera), followed by Proteobacteria- Alphaproteobacteria (10 genera) and Gammaproteobacteria (8 genera), Actinobacteria (8 genera), Bacteroidetes (1genera), and Halomonas (9 genera) representing 38 genera with 105 species. In addition, a few phylogenetically distinct novel groups belonging to the genera Mangrovibacter, Vibrio, Demequina, and Catenococcus were also isolated. PCR-DGGE with the RDP-Classifier program identified the prominent DGGE bands up to genus level namely Bacillus, Pseudomonas, Vibrio, Halomonas, etc. In addition, this study for the first time describes the genera Bhargavaea, Exiguobacterium, Hoeflea, Catenococcus, Albirhodobacter, Dietzia, Brachybacterium, Aerococcus, and Myroides association with mangrove rhizospheres. Likewise, DGGE analysis of archaea represented 2 major groups such as Crenarchaeota and Euryarchaeota, which were further classified into 7 different genera.