Last updated: 2020-06-16

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Knit directory: Fiber_Intervention_Study/

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Make table of sequencial cut-offs where we removed OTUs

This page contains the investigation of the raw data (OTUs) to identify if outliers are present or whether other issues emerge that may influence our results in unexpected ways. This file goes through the following checks:

  1. Removal of Phylum NA features
  2. Computation of total and average prevalence in each Phylum
  3. Removal Phyla with 1% or less of all samples
  4. Computation of total read count for each Phyla
  5. Plotting taxa prevalence vs total counts - identify a natural threshold if clear, if not use 5%
  6. Merging taxa to genus rank/level
  7. Abundance Value Transformations
  8. Plotting of abundance values by “Intervention A or B” before transformation and after
  9. Checking of any bimodal distributions using “subset_taxa” function and plot by “intervention”

Taxonomic Filtering

0. Sample Reads, Totals, and Rarifying

sampleReads <- sample_sums(phylo_data0)

# Total quality Reads
sum(sampleReads)
[1] 532557
# Average reads
mean(sampleReads)
[1] 14393.43
# max sequencing depth
max(sampleReads)
[1] 18990
# rarified to an even depth of
phylo_data0 <- rarefy_even_depth(phylo_data0, replace = T, rngseed = 20200101)
`set.seed(20200101)` was used to initialize repeatable random subsampling.
Please record this for your records so others can reproduce.
Try `set.seed(20200101); .Random.seed` for the full vector
...
25OTUs were removed because they are no longer 
present in any sample after random subsampling
...
# even depth of:
sample_sums(phylo_data0)
Greathouse.FIBER100704 Greathouse.FIBER101008 Greathouse.FIBER100504 
                  7004                   7004                   7004 
Greathouse.FIBER100801 Greathouse.FIBER100812 Greathouse.FIBER100101 
                  7004                   7004                   7004 
Greathouse.FIBER100501 Greathouse.FIBER100301 Greathouse.FIBER100201 
                  7004                   7004                   7004 
Greathouse.FIBER101501 Greathouse.FIBER100308 Greathouse.FIBER100104 
                  7004                   7004                   7004 
Greathouse.FIBER101304 Greathouse.FIBER100912 Greathouse.FIBER100208 
                  7004                   7004                   7004 
Greathouse.FIBER100808 Greathouse.FIBER100708 Greathouse.FIBER101012 
                  7004                   7004                   7004 
Greathouse.FIBER100212 Greathouse.FIBER100904 Greathouse.FIBER100901 
                  7004                   7004                   7004 
Greathouse.FIBER101312 Greathouse.FIBER101201 Greathouse.FIBER100204 
                  7004                   7004                   7004 
Greathouse.FIBER101504 Greathouse.FIBER100804 Greathouse.FIBER101512 
                  7004                   7004                   7004 
Greathouse.FIBER101001 Greathouse.FIBER100304 Greathouse.FIBER100701 
                  7004                   7004                   7004 
Greathouse.FIBER101301 Greathouse.FIBER101508 Greathouse.FIBER100712 
                  7004                   7004                   7004 
Greathouse.FIBER100512 Greathouse.FIBER100908 Greathouse.FIBER101004 
                  7004                   7004                   7004 
Greathouse.FIBER100312 
                  7004 

1. Removal of Phylum NA features

# show ranks
rank_names(phylo_data0)
[1] "Kingdom" "Phylum"  "Class"   "Order"   "Family"  "Genus"  
# table of features for each phylum
table(tax_table(phylo_data0)[,"Phylum"], exclude=NULL)

    __Actinobacteria      __Bacteroidetes      __Cyanobacteria 
                  18                   44                    4 
__Epsilonbacteraeota      __Euryarchaeota         __Firmicutes 
                   1                    2                  317 
      __Fusobacteria      __Lentisphaerae     __Proteobacteria 
                   2                    3                   22 
     __Synergistetes        __Tenericutes    __Verrucomicrobia 
                   1                   12                    1 

Note that no taxa were labels as NA so none were removed.

2. Computation of total and average prevalence in each Phylum

# compute prevalence of each feature
prevdf <- apply(X=otu_table(phylo_data0), 
                MARGIN= ifelse(taxa_are_rows(phylo_data0), yes=1, no=2),
                FUN=function(x){sum(x>0)})
# store as data.frame with labels
prevdf <- data.frame(Prevalence=prevdf,
                     TotalAbundance=taxa_sums(phylo_data0),
                     tax_table(phylo_data0))

Compute the totals and averages abundances.

totals <- plyr::ddply(prevdf, "Phylum",
            function(df1){
              A <- cbind(mean(df1$Prevalence), sum(df1$Prevalence))
              colnames(A) <- c("Average", "Total")
              A
              }
            ) # end

totals
                 Phylum   Average Total
1      __Actinobacteria  4.888889    88
2       __Bacteroidetes 11.159091   491
3       __Cyanobacteria  3.250000    13
4  __Epsilonbacteraeota  3.000000     3
5       __Euryarchaeota  5.500000    11
6          __Firmicutes  9.835962  3118
7        __Fusobacteria  2.500000     5
8       __Lentisphaerae  9.666667    29
9      __Proteobacteria  9.863636   217
10      __Synergistetes  3.000000     3
11        __Tenericutes  4.583333    55
12    __Verrucomicrobia 25.000000    25

The Phylum that appear to be quite low in abundance are Cyanobacteria, Epsilonbacteraeota, Euryarchaeota, Fusobacteria and Synergistetes. However, any of the taxa under a total of 100 may be suspect. First, we will remove the taxa that are clearly too low in abudance (<=5).

filterPhyla <- totals$Phylum[totals$Total <= 5, drop=T] # drop allows some of the attributes to be removed

phylo_data1 <- subset_taxa(phylo_data0, !Phylum %in% filterPhyla)
phylo_data1
phyloseq-class experiment-level object
otu_table()   OTU Table:         [ 423 taxa and 37 samples ]
sample_data() Sample Data:       [ 37 samples by 90 sample variables ]
tax_table()   Taxonomy Table:    [ 423 taxa by 6 taxonomic ranks ]
phy_tree()    Phylogenetic Tree: [ 423 tips and 422 internal nodes ]

Next, we explore the taxa in more detail next as we move to remove some of these low abundance taxa.

3. Removal Phyla with 1% or less of all samples (prevalence filtering)

prevdf1 <- subset(prevdf, Phylum %in% get_taxa_unique(phylo_data1, "Phylum"))

4. Total count computation

# already done above ()

5. Threshold identification

ggplot(prevdf1, aes(TotalAbundance+1,
                    Prevalence/nsamples(phylo_data0))) +
  geom_hline(yintercept=0.01, alpha=0.5, linetype=2)+
  geom_point(size=2, alpha=0.75) +
  scale_x_log10()+
  labs(x="Total Abundance", y="Prevalance [Frac. Samples]")+
  facet_wrap(.~Phylum) + theme(legend.position = "none")

Note: for plotting purposes, a \(+1\) was added to all TotalAbundances to avoid a taking the log of 0.

Next, we define a prevalence threshold, that way the taxa can be pruned to a prespecified level. In this study, we used 0.01 (1%) of total samples.

prevalenceThreshold <- 0.01*nsamples(phylo_data0)
prevalenceThreshold
[1] 0.37
# execute the filtering to this level
keepTaxa <- rownames(prevdf1)[(prevdf1$Prevalence >= prevalenceThreshold)]
phylo_data2 <- prune_taxa(keepTaxa, phylo_data1)

6. Merge taxa (to genus level)

genusNames <- get_taxa_unique(phylo_data2, "Genus")
#phylo_data3 <- merge_taxa(phylo_data2, genusNames, genusNames[which.max(taxa_sums(phylo_data2)[genusNames])])


# How many genera would be present after filtering?
length(get_taxa_unique(phylo_data2, taxonomic.rank = "Genus"))
[1] 155
## [1] 49

phylo_data3 = tax_glom(phylo_data2, "Genus", NArm = TRUE)

7. Relative Adbundance Plot

plot_abundance = function(physeq, title = "", ylab="Abundance"){
  # Arbitrary subset, based on Phylum, for plotting
  #p1f = subset_taxa(physeq, Phylum %in% "__Firmicutes")
  mphyseq = psmelt(physeq)
  mphyseq <- subset(mphyseq, Abundance > 0)
  ggplot(data = mphyseq, mapping = aes_string(x = "Intervention", y = "Abundance")) +
    geom_violin(fill = NA) +
    geom_point(size = 1, alpha = 0.9,
    position = position_jitter(width = 0.3)) +
    scale_y_log10()+
    labs(y=ylab)+
    theme(legend.position="none")
}


# Transform to relative abundance. Save as new object.
phylo_data3ra = transform_sample_counts(phylo_data3, function(x){x / sum(x)})


plotBefore = plot_abundance(phylo_data3, ylab="Abundance prior to transformation")
plotAfter = plot_abundance(phylo_data3ra, ylab="Relative Abundance")
# Combine each plot into one graphic.
grid.arrange(nrow = 2, plotBefore, plotAfter)

Abundance by Phylum

plot_abundance = function(physeq, title = "", Facet = "Phylum", ylab="Abundance"){
  # Arbitrary subset, based on Phylum, for plotting
  #p1f = subset_taxa(physeq, Phylum %in% "__Firmicutes")
  mphyseq = psmelt(physeq)
  mphyseq <- subset(mphyseq, Abundance > 0)
  ggplot(data = mphyseq, mapping = aes_string(x = "Intervention", y = "Abundance")) +
    geom_violin(fill = NA) +
    geom_point(size = 1, alpha = 0.9,
    position = position_jitter(width = 0.3)) +
    facet_wrap(facets = Facet) + scale_y_log10()+
    labs(y=ylab)+
    theme(legend.position="none")
}



plotBefore = plot_abundance(phylo_data3, ylab="Abundance prior to transformation")
plotAfter = plot_abundance(phylo_data3ra, ylab="Relative Abundance")
# Combine each plot into one graphic.
grid.arrange(nrow = 2, plotBefore, plotAfter)

Now, let’s dive into the abundances in more detail. We will investigate the bacteroidetes, firmicute, verrucomicrobia and proteobacteria in more detail (down to the Order).

Phylum: Bacteroidetes

plot_abundance = function(physeq, title = "", Facet = "Order", ylab="Abundance"){
  # Arbitrary subset, based on Phylum, for plotting
  p1f = subset_taxa(physeq, Phylum %in%  "__Bacteroidetes")
  mphyseq = psmelt(p1f)
  mphyseq <- subset(mphyseq, Abundance > 0)
  ggplot(data = mphyseq, mapping = aes_string(x = "Intervention", y = "Abundance")) +
    geom_violin(fill = NA) +
    geom_point(size = 1, alpha = 0.9,
    position = position_jitter(width = 0.3)) +
    facet_wrap(facets = Facet) + scale_y_log10()+
    labs(y=ylab)+
    theme(legend.position="none")
}


plotBefore = plot_abundance(phylo_data3,
                            ylab="Abundance prior to transformation")
plotAfter = plot_abundance(phylo_data3ra,
                           ylab="Relative Abundance")
# Combine each plot into one graphic.
grid.arrange(nrow = 2, plotBefore, plotAfter)

Flav. was only present in intervention group A.

Phylum: Firmicutes

plot_abundance = function(physeq, title = "", Facet = "Order", ylab="Abundance"){
  # Arbitrary subset, based on Phylum, for plotting
  p1f = subset_taxa(physeq, Phylum %in%  "__Firmicutes")
  mphyseq = psmelt(p1f)
  mphyseq <- subset(mphyseq, Abundance > 0)
  ggplot(data = mphyseq, mapping = aes_string(x = "Intervention", y = "Abundance")) +
    geom_violin(fill = NA) +
    geom_point(size = 1, alpha = 0.9,
    position = position_jitter(width = 0.3)) +
    facet_wrap(facets = Facet) + scale_y_log10()+
    labs(y=ylab)+
    theme(legend.position="none")
}


plotBefore = plot_abundance(phylo_data3,
                            ylab="Abundance prior to transformation")
plotAfter = plot_abundance(phylo_data3ra,
                           ylab="Relative Abundance")
# Combine each plot into one graphic.
grid.arrange(nrow = 2, plotBefore, plotAfter)
Warning in max(data$density): no non-missing arguments to max; returning -Inf
Warning: Computation failed in `stat_ydensity()`:
replacement has 1 row, data has 0
Warning in max(data$density): no non-missing arguments to max; returning -Inf
Warning: Computation failed in `stat_ydensity()`:
replacement has 1 row, data has 0

Order: Selenomonadales

plot_abundance = function(physeq, title = "", Facet = "Genus", ylab="Abundance"){
  # Arbitrary subset, based on Phylum, for plotting
  p1f = subset_taxa(physeq, Phylum %in%  "__Firmicutes" & Order %in% "__Selenomonadales" & Family %in% "__Veillonellaceae")
  mphyseq = psmelt(p1f)
  mphyseq <- subset(mphyseq, Abundance > 0)
  ggplot(data = mphyseq, mapping = aes_string(x = "Intervention", y = "Abundance")) +
    geom_violin(fill = NA) +
    geom_point(size = 1, alpha = 0.9,
    position = position_jitter(width = 0.3)) +
    facet_wrap(facets = Facet) + scale_y_log10()+
    labs(y=ylab)+
    theme(legend.position="none")
}


plotBefore = plot_abundance(phylo_data3,
                            ylab="Abundance prior to transformation")
plotAfter = plot_abundance(phylo_data3ra,
                           ylab="Relative Abundance")
# Combine each plot into one graphic.
grid.arrange(nrow = 2, plotBefore, plotAfter)

Family: Veillonellaceae
plot_abundance = function(physeq, title = "", Facet = "Genus", ylab="Abundance"){
  # Arbitrary subset, based on Phylum, for plotting
  p1f = subset_taxa(physeq, Phylum %in%  "__Firmicutes" & Order %in% "__Selenomonadales" & Family %in% "__Veillonellaceae")
  mphyseq = psmelt(p1f)
  mphyseq <- subset(mphyseq, Abundance > 0)
  ggplot(data = mphyseq, mapping = aes_string(x = "Intervention", y = "Abundance")) +
    geom_violin(fill = NA) +
    geom_point(size = 1, alpha = 0.9,
    position = position_jitter(width = 0.3)) +
    facet_wrap(facets = Facet) + scale_y_log10()+
    labs(y=ylab)+
    theme(legend.position="none")
}


plotBefore = plot_abundance(phylo_data3,
                            ylab="Abundance prior to transformation")
plotAfter = plot_abundance(phylo_data3ra,
                           ylab="Relative Abundance")
# Combine each plot into one graphic.
grid.arrange(nrow = 2, plotBefore, plotAfter)

Note the Genus: Allisonella & Megasphaera were only present in Int. Group A.

Phylum: Proteobacteria

plot_abundance = function(physeq, title = "", Facet = "Order", ylab="Abundance"){
  # Arbitrary subset, based on Phylum, for plotting
  p1f = subset_taxa(physeq, Phylum %in%  "__Proteobacteria")
  mphyseq = psmelt(p1f)
  mphyseq <- subset(mphyseq, Abundance > 0)
  ggplot(data = mphyseq, mapping = aes_string(x = "Intervention", y = "Abundance")) +
    geom_violin(fill = NA) +
    geom_point(size = 1, alpha = 0.9,
    position = position_jitter(width = 0.3)) +
    facet_wrap(facets = Facet) + scale_y_log10()+
    labs(y=ylab)+
    theme(legend.position="none")
}


plotBefore = plot_abundance(phylo_data3,
                            ylab="Abundance prior to transformation")
plotAfter = plot_abundance(phylo_data3ra,
                           ylab="Relative Abundance")
# Combine each plot into one graphic.
grid.arrange(nrow = 2, plotBefore, plotAfter)

Phylum: Verrucomicrobia

plot_abundance = function(physeq, title = "", Facet = "Family", ylab="Abundance"){
  # Arbitrary subset, based on Phylum, for plotting
  p1f = subset_taxa(physeq, Phylum %in%  "__Verrucomicrobia")
  mphyseq = psmelt(p1f)
  mphyseq <- subset(mphyseq, Abundance > 0)
  ggplot(data = mphyseq, mapping = aes_string(x = "Intervention", y = "Abundance")) +
    geom_violin(fill = NA) +
    geom_point(size = 1, alpha = 0.9,
    position = position_jitter(width = 0.3)) +
    facet_wrap(facets = Facet) + scale_y_log10()+
    labs(y=ylab)+
    theme(legend.position="none")
}


plotBefore = plot_abundance(phylo_data3,
                            ylab="Abundance prior to transformation")
Warning in prune_taxa(taxa, phy_tree(x)): prune_taxa attempted to reduce tree to 1 or fewer tips.
 tree replaced with NULL.
plotAfter = plot_abundance(phylo_data3ra,
                           ylab="Relative Abundance")
Warning in prune_taxa(taxa, phy_tree(x)): prune_taxa attempted to reduce tree to 1 or fewer tips.
 tree replaced with NULL.
# Combine each plot into one graphic.
grid.arrange(nrow = 2, plotBefore, plotAfter)


sessionInfo()
R version 3.6.3 (2020-02-29)
Platform: x86_64-w64-mingw32/x64 (64-bit)
Running under: Windows 10 x64 (build 18362)

Matrix products: default

locale:
[1] LC_COLLATE=English_United States.1252 
[2] LC_CTYPE=English_United States.1252   
[3] LC_MONETARY=English_United States.1252
[4] LC_NUMERIC=C                          
[5] LC_TIME=English_United States.1252    

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
 [1] cowplot_1.0.0     microbiome_1.8.0  car_3.0-8         carData_3.0-4    
 [5] gvlma_1.0.0.3     patchwork_1.0.0   viridis_0.5.1     viridisLite_0.3.0
 [9] gridExtra_2.3     xtable_1.8-4      kableExtra_1.1.0  plyr_1.8.6       
[13] data.table_1.12.8 readxl_1.3.1      forcats_0.5.0     stringr_1.4.0    
[17] dplyr_0.8.5       purrr_0.3.4       readr_1.3.1       tidyr_1.1.0      
[21] tibble_3.0.1      ggplot2_3.3.0     tidyverse_1.3.0   lmerTest_3.1-2   
[25] lme4_1.1-23       Matrix_1.2-18     vegan_2.5-6       lattice_0.20-38  
[29] permute_0.9-5     phyloseq_1.30.0  

loaded via a namespace (and not attached):
 [1] Rtsne_0.15          minqa_1.2.4         colorspace_1.4-1   
 [4] rio_0.5.16          ellipsis_0.3.1      rprojroot_1.3-2    
 [7] XVector_0.26.0      fs_1.4.1            rstudioapi_0.11    
[10] farver_2.0.3        fansi_0.4.1         lubridate_1.7.8    
[13] xml2_1.3.2          codetools_0.2-16    splines_3.6.3      
[16] knitr_1.28          ade4_1.7-15         jsonlite_1.6.1     
[19] workflowr_1.6.2     nloptr_1.2.2.1      broom_0.5.6        
[22] cluster_2.1.0       dbplyr_1.4.4        BiocManager_1.30.10
[25] compiler_3.6.3      httr_1.4.1          backports_1.1.7    
[28] assertthat_0.2.1    cli_2.0.2           later_1.0.0        
[31] htmltools_0.4.0     tools_3.6.3         igraph_1.2.5       
[34] gtable_0.3.0        glue_1.4.1          reshape2_1.4.4     
[37] Rcpp_1.0.4.6        Biobase_2.46.0      cellranger_1.1.0   
[40] vctrs_0.3.0         Biostrings_2.54.0   multtest_2.42.0    
[43] ape_5.3             nlme_3.1-144        iterators_1.0.12   
[46] xfun_0.14           openxlsx_4.1.5      rvest_0.3.5        
[49] lifecycle_0.2.0     statmod_1.4.34      zlibbioc_1.32.0    
[52] MASS_7.3-51.5       scales_1.1.1        hms_0.5.3          
[55] promises_1.1.0      parallel_3.6.3      biomformat_1.14.0  
[58] rhdf5_2.30.1        curl_4.3            yaml_2.2.1         
[61] stringi_1.4.6       S4Vectors_0.24.4    foreach_1.5.0      
[64] BiocGenerics_0.32.0 zip_2.0.4           boot_1.3-24        
[67] rlang_0.4.6         pkgconfig_2.0.3     evaluate_0.14      
[70] Rhdf5lib_1.8.0      labeling_0.3        tidyselect_1.1.0   
[73] magrittr_1.5        R6_2.4.1            IRanges_2.20.2     
[76] generics_0.0.2      DBI_1.1.0           foreign_0.8-75     
[79] pillar_1.4.4        haven_2.3.0         whisker_0.4        
[82] withr_2.2.0         mgcv_1.8-31         abind_1.4-5        
[85] survival_3.1-8      modelr_0.1.8        crayon_1.3.4       
[88] rmarkdown_2.1       grid_3.6.3          blob_1.2.1         
[91] git2r_0.27.1        reprex_0.3.0        digest_0.6.25      
[94] webshot_0.5.2       httpuv_1.5.2        numDeriv_2016.8-1.1
[97] stats4_3.6.3        munsell_0.5.0