Comparative Study of Bacterial Communities in Nepenthes Pitchers and Their Correlation to Species and Fluid Acidity

Abstract

Pitchers are specialized digestive organs of carnivorous plants which evolved for trapping prey and represent a unique environment harboring hidden diversity of unexplored microbes forming transient hydrolytic microcosms. In this study, the diversity of bacterial communities in the pitcher fluids of seven local Nepenthes found in Thailand was assessed by tagged 16S ribosomal RNA (rRNA) gene amplicon sequencing on an Ion PGM™ platform. A total of 1,101,000 filtered sequences were obtained which were taxonomically classified into 20 phyla, 48 classes, 72 orders, 153 families, and 442 genera while the remainder (1.43 %) could not be assigned to any existing taxa. Proteobacteria represented the predominant members in closed pitchers and more diversified bacterial taxa particularly Bacteriodetes and Actinobacteria, showed increasing abundance in open pitchers containing insect bodies. Principal coordinate analysis revealed that distribution of bacterial taxa was not significantly related to the Nepenthes species but strongly correlated to the pH of the pitcher fluids (pH 1.7-6.7). Acidicella was a highly dominant bacterial genus in acidic pitcher fluids while Dyella and Mycobacterium were also common genera in most pitchers. A unique microbial community structure was found in Nepenthes ampullaria which could reflect their adaptation to digest leaf litter, in addition to insect prey. The work revealed the highly unexplored nature of bacterial microcosms in Nepenthes pitcher fluids and provides insights into their community structure in this unique ecological system.

Convergence between the microcosms of Southeast Asian and North American pitcher plants

“…ordisurf R 2 = 0.74, p<0.001; mantel r = 0.63, p<0.001). This result supports a recent study that also noted a correlation between pitcher fluid pH and Nepenthes bacteria ( Kanokratana et al, 2016 ). But the strong effect of pH on bacterial community composition is not driven by Nepenthes species differences per se; significant, high correlations between pH and bacterial community composition are also found within each of the three species with very low pH values when the data of each species are analyzed alone (Mantel tests: N. gracilis r = 0.46, p<0.001; N. rafflesiana r = 0.68, p<0.001; N. stenophylla r = 0.85, p<0.001).…”

Investigation of an Elevational Gradient Reveals Strong Differences Between Bacterial and Eukaryotic Communities Coinhabiting Nepenthes Phytotelmata

“…Nepenthes phytotelm communities typically include bacteria, fungi, algae, protozoans, mites, and aquatic insect larvae [ 47 , 49 , 59 ], and, occasionally, anuran tadpoles [ 61 – 63 ] and crabs [ 64 ]. Previous metabarcoding studies show that their communities are specialized and distinct from the surrounding environment [ 65 ], which can be attributed to the specific conditions within the plants such as the acidic pH levels of the fluids [ 65 , 66 ].…”

Transcriptome-wide shift from photosynthesis and energy metabolism upon endogenous fluid protein depletion in young Nepenthes ampullaria pitchers

“…For example, prey induced pitcher fluid acidification via the upregulation of a plasma membrane H + -ATPase 47 . Indeed, H + ion fluxes are actively controlled in opened pitchers of N. ampullaria to maintain the commensals in less acidic pitcher fluids 28,30 . Four highly expressed aquaporins (1.A.8) for water transport (TR35579|c0_g1, TR58374|c0_g2, TR64049|c0_g1, and TR45806|c0_g1) were downregulated in D3C pitchers (Fig.…”

“…Pitchers of N. ampullaria are long-lived with a feeding period of over 8 months 27 and adapted for slow and steady ammonium (NH 4 + ) uptake from the slow breakdown of plant materials by commensal microbes, compared to short-lived (≤ 3 months) pitchers with high turnover and prey capture rates 28 . Pitcher fluids of N. ampullaria are less acidic to maintain infauna (mosquito larvae and bacteria) for leaf litter decomposition and nutrient mineralisation 29,30 . Over half of the biomass of dead matter in the pitchers was plant-derived 31 , in which >35% of leaf nitrogen (N) is obtained from fallen leaves containing only 1.2% N 26,32 .…”