Maas KR

References (2)

Title : Non-symbiotic Bradyrhizobium ecotypes dominate North American forest soils - VanInsberghe_2015_ISME.J_9_2435
Author(s) : VanInsberghe D , Maas KR , Cardenas E , Strachan CR , Hallam SJ , Mohn WW
Ref : Isme J , 9 :2435 , 2015
Abstract : The genus Bradyrhizobium has served as a model system for studying host-microbe symbiotic interactions and nitrogen fixation due to its importance in agricultural productivity and global nitrogen cycling. In this study, we identify a bacterial group affiliated with this genus that dominates the microbial communities of coniferous forest soils from six distinct ecozones across North America. Representative isolates from this group were obtained and characterized. Using quantitative population genomics, we show that forest soil populations of Bradyrhizobium represent ecotypes incapable of nodulating legume root hairs or fixing atmospheric nitrogen. Instead, these populations appear to be free living and have a greater potential for metabolizing aromatic carbon sources than their close symbiotic relatives. In addition, we identify fine-scaled differentiation between populations inhabiting neighboring soil layers that illustrate how diversity within Bradyrhizobium is structured by habitat similarity. These findings reconcile incongruent observations about this widely studied and important group of bacteria and highlight the value of ecological context to interpretations of microbial diversity and taxonomy. These results further suggest that the influence of this genus likely extends well beyond facilitating agriculture, especially as forest ecosystems are large and integral components of the biosphere. In addition, this study demonstrates how focusing research on economically important microorganisms can bias our understanding of the natural world.
ESTHER : VanInsberghe_2015_ISME.J_9_2435
PubMedSearch : VanInsberghe_2015_ISME.J_9_2435
PubMedID: 25909973
Gene_locus related to this paper: 9brad-a0a0d7njr6 , 9brad-a0a0d7nke7 , 9brad-a0a0d7p9x5 , 9brad-a0a0d7pif1 , 9brad-a0a0d7p1j9 , 9brad-a0a0d7qiy7 , 9brad-a0a0d7pry5

Title : Genomic properties of Marine Group A bacteria indicate a role in the marine sulfur cycle - Wright_2014_ISME.J_8_455
Author(s) : Wright JJ , Mewis K , Hanson NW , Konwar KM , Maas KR , Hallam SJ
Ref : Isme J , 8 :455 , 2014
Abstract : Marine Group A (MGA) is a deeply branching and uncultivated phylum of bacteria. Although their functional roles remain elusive, MGA subgroups are particularly abundant and diverse in oxygen minimum zones and permanent or seasonally stratified anoxic basins, suggesting metabolic adaptation to oxygen-deficiency. Here, we expand a previous survey of MGA diversity in O2-deficient waters of the Northeast subarctic Pacific Ocean (NESAP) to include Saanich Inlet (SI), an anoxic fjord with seasonal O2 gradients and periodic sulfide accumulation. Phylogenetic analysis of small subunit ribosomal RNA (16S rRNA) gene clone libraries recovered five previously described MGA subgroups and defined three novel subgroups (SHBH1141, SHBH391, and SHAN400) in SI. To discern the functional properties of MGA residing along gradients of O2 in the NESAP and SI, we identified and sequenced to completion 14 fosmids harboring MGA-associated 16S RNA genes from a collection of 46 fosmid libraries sourced from NESAP and SI waters. Comparative analysis of these fosmids, in addition to four publicly available MGA-associated large-insert DNA fragments from Hawaii Ocean Time-series and Monterey Bay, revealed widespread genomic differentiation proximal to the ribosomal RNA operon that did not consistently reflect subgroup partitioning patterns observed in 16S rRNA gene clone libraries. Predicted protein-coding genes associated with adaptation to O2-deficiency and sulfur-based energy metabolism were detected on multiple fosmids, including polysulfide reductase (psrABC), implicated in dissimilatory polysulfide reduction to hydrogen sulfide and dissimilatory sulfur oxidation. These results posit a potential role for specific MGA subgroups in the marine sulfur cycle.
ESTHER : Wright_2014_ISME.J_8_455
PubMedSearch : Wright_2014_ISME.J_8_455
PubMedID: 24030600
Gene_locus related to this paper: 9bact-s4w428