knitr::opts_chunk$set(message = FALSE, warning = FALSE, comment = NA, fig.width = 6.25, fig.height = 5) library(ANCOMBC) library(tidyverse) library(DT) options(DT.options = list( initComplete = JS("function(settings, json) {", "$(this.api().table().header()).css({'background-color': '#000', 'color': '#fff'});","}")))
Analysis of Compositions of Microbiomes with Bias Correction (ANCOM-BC) [@lin2020analysis] is a methodology of differential abundance (DA) analysis for microbial absolute abundances. ANCOM-BC estimates the unknown sampling fractions, corrects the bias induced by their differences through a log linear regression model including the estimated sampling fraction as an offset terms, and identifies taxa that are differentially abundant according to the variable of interest. For more details, please refer to the ANCOM-BC paper.
Download package.
if (!requireNamespace("BiocManager", quietly = TRUE)) install.packages("BiocManager") BiocManager::install("ANCOMBC")
Load the package.
library(ANCOMBC)
The HITChip Atlas dataset contains genus-level microbiota profiling with HITChip for 1006 western adults with no reported health complications, reported in [@lahti2014tipping]. The dataset is available via the microbiome R package [@lahti2017tools] in phyloseq [@mcmurdie2013phyloseq] format. In this tutorial, we consider the following covariates:
Continuous covariates: "age"
Categorical covariates: "region", "bmi"
The group variable of interest: "bmi"
Three groups: "lean", "overweight", "obese"
The reference group: "obese"
data(atlas1006, package = "microbiome") # Subset to baseline pseq = phyloseq::subset_samples(atlas1006, time == 0) # Re-code the bmi group meta_data = microbiome::meta(pseq) meta_data$bmi = recode(meta_data$bmi_group, obese = "obese", severeobese = "obese", morbidobese = "obese") # Note that by default, levels of a categorical variable in R are sorted # alphabetically. In this case, the reference level for `bmi` will be # `lean`. To manually change the reference level, for instance, setting `obese` # as the reference level, use: meta_data$bmi = factor(meta_data$bmi, levels = c("obese", "overweight", "lean")) # You can verify the change by checking: # levels(meta_data$bmi) # Create the region variable meta_data$region = recode(as.character(meta_data$nationality), Scandinavia = "NE", UKIE = "NE", SouthEurope = "SE", CentralEurope = "CE", EasternEurope = "EE", .missing = "unknown") phyloseq::sample_data(pseq) = meta_data # Subset to lean, overweight, and obese subjects pseq = phyloseq::subset_samples(pseq, bmi %in% c("lean", "overweight", "obese")) # Discard "EE" as it contains only 1 subject # Discard subjects with missing values of region pseq = phyloseq::subset_samples(pseq, ! region %in% c("EE", "unknown")) print(pseq)
ancombc
function using the phyloseq
objectout = ancombc(data = pseq, tax_level = "Family", formula = "age + region + bmi", p_adj_method = "holm", prv_cut = 0.10, lib_cut = 1000, group = "bmi", struc_zero = TRUE, neg_lb = TRUE, tol = 1e-5, max_iter = 100, conserve = TRUE, alpha = 0.05, global = TRUE, n_cl = 1, verbose = TRUE) res = out$res res_global = out$res_global
Tests for interactions are supported by specifying the interactions in the fix_formula
.
Please ensure that interactions between variables are included using the *
operator,
as the :
operator is not recognized by the ancombc
function and will result in an error.
Additionally, when the group
variable contains interaction terms, only the main effect
will be considered in multi-group comparisons.
out = ancombc(data = pseq, tax_level = "Family", formula = "age + region * bmi", p_adj_method = "holm", prv_cut = 0.10, lib_cut = 1000, group = "bmi", struc_zero = TRUE, neg_lb = TRUE, tol = 1e-5, max_iter = 100, conserve = TRUE, alpha = 0.05, global = TRUE, n_cl = 1, verbose = TRUE) res = out$res res_global = out$res_global
Result from the ANCOM-BC log-linear model to determine taxa that are differentially abundant according to the covariate of interest. It contains: 1) log fold changes; 2) standard errors; 3) test statistics; 4) p-values; 5) adjusted p-values; 6) indicators whether the taxon is differentially abundant (TRUE) or not (FALSE).
tab_lfc = res$lfc col_name = c("Taxon", "Intercept", "Age", "NE - CE", "SE - CE", "US - CE", "Overweight - Obese", "Lean - Obese") colnames(tab_lfc) = col_name tab_lfc %>% datatable(caption = "Log Fold Changes from the Primary Result") %>% formatRound(col_name[-1], digits = 2)
tab_se = res$se colnames(tab_se) = col_name tab_se %>% datatable(caption = "SEs from the Primary Result") %>% formatRound(col_name[-1], digits = 2)
tab_w = res$W colnames(tab_w) = col_name tab_w %>% datatable(caption = "Test Statistics from the Primary Result") %>% formatRound(col_name[-1], digits = 2)
tab_p = res$p_val colnames(tab_p) = col_name tab_p %>% datatable(caption = "P-values from the Primary Result") %>% formatRound(col_name[-1], digits = 2)
tab_q = res$q colnames(tab_q) = col_name tab_q %>% datatable(caption = "Adjusted p-values from the Primary Result") %>% formatRound(col_name[-1], digits = 2)
tab_diff = res$diff_abn colnames(tab_diff) = col_name tab_diff %>% datatable(caption = "Differentially Abundant Taxa from the Primary Result")
To obtain bias-corrected abundances, the following steps can be taken:
Step 1: Calculate the estimated sample-specific sampling fractions, in log scale.
Step 2: Correct the log observed abundances by subtracting the estimated sampling fraction from the log observed abundances of each sample.
It is important to note that we can only estimate sampling fractions up to an additive constant, meaning that only the difference between bias-corrected abundances is meaningful. Additionally, taxon-specific biases are not taken into account in the calculation of bias-corrected abundances, as it is assumed that these biases vary across taxa but remain constant across samples within a taxon.
samp_frac = out$samp_frac # Replace NA with 0 samp_frac[is.na(samp_frac)] = 0 # Add pesudo-count (1) to avoid taking the log of 0 log_obs_abn = log(out$feature_table + 1) # Adjust the log observed abundances log_corr_abn = t(t(log_obs_abn) - samp_frac) # Show the first 6 samples round(log_corr_abn[, 1:6], 2) %>% datatable(caption = "Bias-corrected log observed abundances")
df_lfc = data.frame(res$lfc[, -1] * res$diff_abn[, -1], check.names = FALSE) %>% mutate(taxon_id = res$diff_abn$taxon) %>% dplyr::select(taxon_id, everything()) df_se = data.frame(res$se[, -1] * res$diff_abn[, -1], check.names = FALSE) %>% mutate(taxon_id = res$diff_abn$taxon) %>% dplyr::select(taxon_id, everything()) colnames(df_se)[-1] = paste0(colnames(df_se)[-1], "SE") df_fig_age = df_lfc %>% dplyr::left_join(df_se, by = "taxon_id") %>% dplyr::transmute(taxon_id, age, ageSE) %>% dplyr::filter(age != 0) %>% dplyr::arrange(desc(age)) %>% dplyr::mutate(direct = ifelse(age > 0, "Positive LFC", "Negative LFC")) df_fig_age$taxon_id = factor(df_fig_age$taxon_id, levels = df_fig_age$taxon_id) df_fig_age$direct = factor(df_fig_age$direct, levels = c("Positive LFC", "Negative LFC")) p_age = ggplot(data = df_fig_age, aes(x = taxon_id, y = age, fill = direct, color = direct)) + geom_bar(stat = "identity", width = 0.7, position = position_dodge(width = 0.4)) + geom_errorbar(aes(ymin = age - ageSE, ymax = age + ageSE), width = 0.2, position = position_dodge(0.05), color = "black") + labs(x = NULL, y = "Log fold change", title = "Log fold changes as one unit increase of age") + scale_fill_discrete(name = NULL) + scale_color_discrete(name = NULL) + theme_bw() + theme(plot.title = element_text(hjust = 0.5), panel.grid.minor.y = element_blank(), axis.text.x = element_text(angle = 60, hjust = 1)) p_age
df_fig_bmi = df_lfc %>% filter(bmioverweight != 0 | bmilean != 0) %>% transmute(taxon_id, `Overweight vs. Obese` = round(bmioverweight, 2), `Lean vs. Obese` = round(bmilean, 2)) %>% pivot_longer(cols = `Overweight vs. Obese`:`Lean vs. Obese`, names_to = "group", values_to = "value") %>% arrange(taxon_id) lo = floor(min(df_fig_bmi$value)) up = ceiling(max(df_fig_bmi$value)) mid = (lo + up)/2 p_bmi = df_fig_bmi %>% ggplot(aes(x = group, y = taxon_id, fill = value)) + geom_tile(color = "black") + scale_fill_gradient2(low = "blue", high = "red", mid = "white", na.value = "white", midpoint = mid, limit = c(lo, up), name = NULL) + geom_text(aes(group, taxon_id, label = value), color = "black", size = 4) + labs(x = NULL, y = NULL, title = "Log fold changes as compared to obese subjects") + theme_minimal() + theme(plot.title = element_text(hjust = 0.5)) p_bmi
Result from the ANCOM-BC global test to determine taxa that are differentially abundant between at least two groups across three or more different groups. In this example, we want to identify taxa that are differentially abundant between at least two regions across CE, NE, SE, and US. The result contains: 1) test statistics; 2) p-values; 3) adjusted p-values; 4) indicators whether the taxon is differentially abundant (TRUE) or not (FALSE).
tab_w = res_global[, c("taxon", "W")] tab_w %>% datatable(caption = "Test Statistics from the Global Test Result") %>% formatRound(c("W"), digits = 2)
tab_p = res_global[, c("taxon", "p_val")] tab_p %>% datatable(caption = "P-values from the Global Test Result") %>% formatRound(c("p_val"), digits = 2)
tab_q = res_global[, c("taxon", "q_val")] tab_q %>% datatable(caption = "Adjusted p-values from the Global Test Result") %>% formatRound(c("q_val"), digits = 2)
tab_diff = res_global[, c("taxon", "diff_abn")] tab_diff %>% datatable(caption = "Differentially Abundant Taxa from the Global Test Result")
sig_taxa = res_global %>% dplyr::filter(diff_abn == TRUE) %>% .$taxon df_bmi = tab_lfc %>% dplyr::select(Taxon, `Overweight - Obese`, `Lean - Obese`) %>% filter(Taxon %in% sig_taxa) df_heat = df_bmi %>% pivot_longer(cols = -one_of("Taxon"), names_to = "region", values_to = "value") %>% mutate(value = round(value, 2)) df_heat$Taxon = factor(df_heat$Taxon, levels = sort(sig_taxa)) lo = floor(min(df_heat$value)) up = ceiling(max(df_heat$value)) mid = (lo + up)/2 p_heat = df_heat %>% ggplot(aes(x = region, y = Taxon, fill = value)) + geom_tile(color = "black") + scale_fill_gradient2(low = "blue", high = "red", mid = "white", na.value = "white", midpoint = mid, limit = c(lo, up), name = NULL) + geom_text(aes(region, Taxon, label = value), color = "black", size = 4) + labs(x = NULL, y = NULL, title = "Log fold changes for globally significant taxa") + theme_minimal() + theme(plot.title = element_text(hjust = 0.5)) p_heat
ancombc
function using the tse
objecttse = mia::makeTreeSummarizedExperimentFromPhyloseq(pseq) out = ancombc(data = tse, assay_name = "counts", tax_level = "Family", formula = "age + region + bmi", p_adj_method = "holm", prv_cut = 0.10, lib_cut = 1000, group = "bmi", struc_zero = TRUE, neg_lb = TRUE, tol = 1e-5, max_iter = 100, conserve = TRUE, alpha = 0.05, global = TRUE, n_cl = 1, verbose = TRUE) res = out$res res_global = out$res_global
ancombc
function by directly providing the abundance and metadataabundance_data = microbiome::abundances(pseq) aggregate_data = microbiome::abundances(microbiome::aggregate_taxa(pseq, "Family")) meta_data = microbiome::meta(pseq) out = ancombc(data = abundance_data, aggregate_data = aggregate_data, meta_data = meta_data, formula = "age + region + bmi", p_adj_method = "holm", prv_cut = 0.10, lib_cut = 1000, group = "bmi", struc_zero = TRUE, neg_lb = TRUE, tol = 1e-5, max_iter = 100, conserve = TRUE, alpha = 0.05, global = TRUE, n_cl = 1, verbose = TRUE) res = out$res res_global = out$res_global
sessionInfo()
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