Phylogenetic Diversity of Diazotrophs along an Experimental Nutrient Gradient in Mangrove Sediments

Abstract

Abstract:The diversity of diazotrophs was studied in the sediment of mangrove forests (Twin Cays, Belize) subjected to a long-term fertilization with nitrogen and phosphorus. Terminal Restriction Fragment Length Polymorphism (TRFLP) and cloning of PCR-amplified nifH genes were combined via in silico analysis to assign clones to TRFLP-nifH phylotypes, as well as to characterize the occurrence of phylotypes in response to environmental conditions. Results indicated that mangrove sediments from Belize harbor a unique diazotrophic community with a low metabolic diversity dominated by sulfate reducers. The variability of potential nitrogen-fixing sulfate reducers was explained by several environmental parameters, primarily by the abundance of dead roots in the sediments, and the concentration of H2S in the pore-waters. This study describes the complexity of microbial communities within the mangrove sediments with specific functional groups varying along environmental gradients.

Anthropogenic impact on diazotrophic diversity in the mangrove rhizosphere revealed by nifH pyrosequencing

“…Proteobacteria usually form a distinct cluster and archaeal nitrogenases, including homologues of both functional nitrogenases and nif -like genes of unknown function, have thus far only been found in methanogens ( Chien et al, 2000 ). In our study, the Cluster III diazotrophs were composed entirely of the sulfate-reducing bacteria, which are very common in lake beds ( Bak and Pfennig, 1991 ) and mangrove sediments ( Lyimo et al, 2002 ; Varon-Lopez et al, 2014 ; Romero et al, 2015 ). It has been reported that they are dominant in mangrove sediments that are subjected to long-term fertilization with nitrogen and phosphorus ( Romero et al, 2015 ).…”

“…This might be explained by the fact that our study was based on nifH sequences at rDNA level, and therefore did not reflect the activity of nitrogenase per se . More importantly, these two locations were dominated by sulfate-reducing bacteria, which are known to be involved in nitrogen fixation and sulfate reduction as well as playing a key role in sedimentary cycling of N, C, and S ( Lyimo et al, 2002 ; Varon-Lopez et al, 2014 ; Romero et al, 2015 ).…”

“…No specific associations have been found between the mangrove tree species and the nitrogen-fixing bacteria that were isolated. Instead, fertilizer and organic amendments, such as oil ( Dias et al, 2012 ) and polycyclic aromatic hydrocarbons ( Sun et al, 2012 ), along with the bioavailability of nutrients ( Romero et al, 2012 , 2015 ), have caused significant alterations in the diazotroph communities in different mangrove ecosystems. Rhizosphere diazotrophs are not only affected by root–bacteria interactions, but are also driven by the geochemical parameters in sediments ( Zhang et al, 2008 ; Romero et al, 2012 ).…”

Unexpected Nitrogen Sources in a Tropical Urban Estuary

“…The hypothesis that fits all the geochemical observations is that the sediments and water column of the CMP are hot spots for microbes that fix nitrogen during sulfate reduction. The only probable explanation for low δ 15 N values in this area is N‐fixation, and it is well documented that S‐reducers in mangrove ecosystems also fix N (Romero et al, ; Shiau et al, ). We suggest that the δ 34 S values are so high because the flushing in this part of the estuary is poor, forcing the microbial communities to reduce the heavier 34 S that they would otherwise preferentially avoid (e.g., Emery & Robinson, ).…”

Ciclagem de nitrogênio no solo de manguezal em diferentes estágios de regeneração em Fortaleza (CE)

“…Devido às baixas taxas de decomposição da matéria orgânica, a maior entrada de N em manguezais preservados é através da FBN (HOLGUIN et al, 2001) com altas taxas de fixação no solo e associadas à rizosfera (ALFARO-ESPINOZA; ULLRICH, 2015), mediada por uma complexa comunidade microbiana, com redundância funcional capaz de integrar os processos biogeoquímicos e garantir, além da FBN, a oxidação da matéria orgânica pela redução do sulfato (ROMERO et al, 2015). No entanto, fatores ambientais específicos como O2, formas inorgânicas de N e a disponibilidade de C como fonte de energia podem limitar a FBN (MOREIRA; SIQUEIRA, 2006;ROMERO et al, 2015).…”