Mangrove bacterial richness

Abstract

Mangroves are complex and dynamic ecosystems varying in salinity, water level and nutrient availability; they also contain diverse and distinct microbial communities. Studies of microbes and their interactions with other ecosystem components (e.g., tree roots) are critical for our understanding of mangrove ecosystem functioning and remediation. Using a barcoding pyrosequencing approach, we previously noted the persistence of terrestrial bacterial populations on mangrove roots when nursery raised saplings were transplanted back to their natural environment. Here we go into further detail about the potential functional associations of bacterial guilds with distinct mangrove microhabitats including the rhizosphere. We also use a nonparametric richness estimator to show that estimated operational taxonomic unit (OTU) richness is more than twice that observed. In the transplant microhabitat, our estimate suggests that there are almost 7000 OTU's for a sample size of 10400 individual sequences with no sign of an asymptote, indicating that 'true' richness for this microhabitat is substantially larger. Results on the number of bacterial OTU's should, however, be viewed with caution given that the barcoding pyrosequencing technique used can yield sequencing artifacts that may inflate richness estimates if not properly removed.

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Acknowledgments

This study was funded by the German Research Foundation SM59/4-1 and 4-2 (www.dfg.de/en/index.jsp), FAPERJ-Brazil (www.faperj.br), Centre for Environmental and Marine Studies (CESAM, Portugal) (www.cesam.ua.pt) and Foundation for Science and Technology (FCT, Portugal) PTDC/AAC-CLI/107916/2008 (alfa.fct.mctes.pt).

Figures and Tables

Figure 1 Bacterial richness in mangrove sediments and rhizospheres estimated using rarefaction. Four microhabitats were sampled: Nur, roots of nursery plants before planting in a mangrove; Trn, roots of transplanted saplings 202 days after planting in a mangrove; Trn-n, roots of transplanted saplings 202 days after planting without OTU's shared between the nursery and the transplants; Nat, roots of native (non-transplanted) saplings in a mangrove (Nat); and Bul, bulk sediment in the mangrove replant area. Four replicates per habitat were surveyed. The species accumulation curves shown represent values for pooled replicates.

Figure 2 Bacterial richness in mangrove sediments and rhizospheres estimated with the Chao1 richness estimator. Four microhabitats were sampled: Nur, roots of nursery plants before planting in a mangrove; Trn, roots of transplanted saplings 202 days after planting in a mangrove; Trn-n, roots of transplanted saplings 202 days after planting without OTU's shared between the nursery and the transplants. Nat, roots of native (non-transplanted) saplings in a mangrove (Nat); and Bul, bulk sediment in the mangrove replant area. Four replicates per habitat were surveyed.

Addendum to: