Ashley Campbell edited Results_and_Discussion.tex  over 9 years ago

Commit id: e47390500f4d9475e0496b278637ecba7bff8c19

deletions | additions      

       

\textit{Xylose}. Within the first 7 days of incubation an average 63\% of \textsuperscript{13}C-xylose was respired and only an additional 6\% more was respired between days 7 and 30 (\href{https://authorea.com/users/3537/articles/8459/master/file/figures/Percent_respired_13C/Percent_respired_13C.png}{Table S1}). At the end of the 30 day experiment 30\% of the original \textsuperscript{13}C from xylose remained in the soils. The \textsuperscript{13}C remaining in the soil from \textsuperscript{13}C-xylose addition has likely been stabilized by assimilation into microbial biomass and/or microbial conversion into other forms of organic matter, though it is possible that some \textsuperscript{13}C-xylose remains unavailable to microbes due to abiotic interactions in soil \cite{Kalbitz_2000}. Of the 60 total xylose responders 53 were responsive within the first 7 days and only 7 responders detected for days 14 and 30 (\href{https://authorea.com/users/3537/articles/8459/master/file/figures/resp_table/resp_table.png}{Table S1}).   At day 1 (d1), 57\% of xylose responsive OTUs belong to Firmicutes (Paenibacillaceae, Planococcaceae, and Bacillaceae) and the remaining 43\% of responders were comprised of 19\% Bacteroidetes (Flavobacteriaceae), 14\% Proteobacteria (Enterobacteriaceae, Comamonadaceae, and uncultured Gammaproteobacteria), and 10\% Actinobacteria (Micrococcaceae and Microbacteriaceae) (\href{https://www.authorea.com/users/3537/articles/3612/master/file/figures/l2fc_fig1/l2fc_fig.pdf}{Fig. 2}). Of the xylose responders detected at day 3 (d3), Firmicutes responders decreased to 8\% (from 12 OTUs to 1) and an increase in Bacteroidetes (67\%) and Proteobacteria (25\%) from d1. Cellvibrio, a canonical cellulose degrader, was noteably notably  one of the three Proteobacterial xylose responders at d3 (discussed later). Day 7 (d7) responders were 50\% Actinobacteria, 35\% Proteobacteria, and 5\% of each Bacteroidetes, Firmicutes, and Planctomycetes. A substantial amount (75\%) of xylose responders for day 7 had not previously been identified as responders at earlier time points which attests to the wide number of taxa able to use xylose. Each of the 10 Actinobacteria responders at day 7 belonged to a different family making it the phylum with the most wide-spread use of xylose. However, it should be noted that they were confined within two Actinobacterial Orders; Frankiales and Micrococcales. We observe dynamic changes in \textsuperscript{13}C-xylose assimilation with time; dominant xylose responders shift from Firmicutes (d1) to Bacteroidetes (d3) then finally Actinobacteria (d7). At any given time soils harbor microorganisms at varying degrees of dormancy depending on nutrient availability \cite{Jones_2010}. The sudden addition of our complex C mixture would most certainly prompt dormant and non-dormant microbes back into metabolic activity, with those exhibiting higher rRNA operon copy numbers responding the fastest. The responders identified at d1 for xylose utilization have all been noted for exhibiting some form of dormancy strategy \cite{Jones_2010, Mulyukin_2009, Darcy_2011, Sachidanandham_2008, Finkel_2006, Rittershaus_2013, Tada_2013, Lay_2013}, though the only spore-forming responders at d1 are Firmicutes. Additionally, d1 responders exhibit 6-14 rRNA operon copies with the exception of the Betaproteobacteria Comamonadaceae and the Actinobacterial OTUs which exhibit 1-2 copies according to representative taxa in the rrnDB v. 3.1.227 \cite{18948294,11125085}. With the exception of the single Firmicutes (Paenibacillaceae), responders on d3 possess 3-6 rRNA operon copies, less than responders on d1. Similar to d3, 85\% of d7 responders exhibit between 1-5 rRNA operon copies with the remaining 15\% (Flavobacteriaceae, Enterobacteriaceae, and Paenibacillaceae) containing between 6-14 rRNA operon copies. Paenibacillus (100\% identity) was the only OTU to be identified at every time point (up to day 30) as a xylose responder. This result suggests that large numbers of cells from Paenibacillus sporulated after \textsuperscript{13}C-labeling of their DNA and that these spores remained throughout the experiment. It was the the second most enriched xylose responder, log\text$_{2}$fold change (l2fc) of 3.5, measured in the time series second only to a Gammaproteobacteria (Xanthomonadaceae; l2fc = 3.7).