Microbial rhodopsins on leaf surfaces of terrestrial plants

Author Posting. © The Author(s), 2011. This is the author's version of the work. It is posted here by permission of John Wiley & Sons for personal use, not for redistribution. The definitive version was published in Environmental Microbiology 14 (2012): 140-146, doi:10.1111/j.1462-2920.2011.02554.x.The above-ground surfaces of terrestrial plants, the phyllosphere, comprise the main interface between the terrestrial biosphere and solar radiation. It is estimated to host up to 1026 microbial cells that may intercept part of the photon flux impinging on the leaves. Based on 454- pyrosequencing generated metagenome data, we report on the existence of diverse microbial rhodopsins in five distinct phyllospheres from tamarisk (Tamarix nilotica), soybean (Glycine max), Arabidopsis (Arabidopsis thaliana), clover (Trifolium repens) and rice (Oryza sativa). Our findings, for the first time describing microbial rhodopsins from non-aquatic habitats, point toward the potential coexistence of microbial rhodopsin-based phototrophy and plant chlorophyll-based photosynthesis, with the different pigments absorbing non-overlapping fractions of the light spectrum.This work was supported in part by a grant from Bridging the Rift Foundation (O.B. & S.B.), Israel Science Foundation grant 1203/06 (O.B.), the Gruss-Lipper Family Foundation at MBL (O.M.F., S.B. & A.F.P.), a US-Israel Binational Science Foundation grant 2006324 (S.B.), and DOE National Institutes of Health Grant R37GM27750, Department of Energy Grant DE-FG02-07ER15867, and endowed chair AU-0009 from the Robert A. Welch Foundation (J.L.S.)

Bacterial anoxygenic photosynthesis on plant leaf surfaces

The aerial surface of plants, the phyllosphere, is colonized by numerous bacteria displaying diverse metabolic properties that enable their survival in this specific habitat. Recently, we reported on the presence of microbial rhodopsin harbouring bacteria on the top of leaf surfaces. Here, we report on the presence of additional bacterial populations capable of harvesting light as a means of supplementing their metabolic requirements. An analysis of six phyllosphere metagenomes revealed the presence of a diverse community of anoxygenic phototrophic bacteria, including the previously reported methylobacteria, as well as other known and unknown phototrophs. The presence of anoxygenic phototrophic bacteria was also confirmed in situ by infrared epifluorescence microscopy. The microscopic enumeration correlated with estimates based on metagenomic analyses, confirming both the presence and high abundance of these microorganisms in the phyllosphere. Our data suggest that the phyllosphere contains a phylogenetically diverse assemblage of phototrophic species, including some yet undescribed bacterial clades that appear to be phyllosphere-unique

Widespread distribution of proteorhodopsins in freshwater and brackish ecosystems

Proteorhodopsins (PRs) are light-driven proton pumps that have been found in a variety of marine environments. The goal of this study was to search for PR presence in different freshwater and brackish environments and to explore the diversity of non-marine PR protein. Here, we show that PRs exist in distinctly different aquatic environments, ranging from clear water lakes to peat lakes and in the Baltic Sea. Some of the PRs observed in this study formed unique clades that were not previously observed in marine environments, whereas others were similar to PRs found in non-marine samples of the Global Ocean Sampling (GOS) expedition. Furthermore, the similarity of several PRs isolated from lakes in different parts of the world suggests that these genes are dispersed globally and that they may encode unique functional capabilities enabling successful competition in a wide range of freshwater environments. Phylogenomic analysis of genes found on these GOS scaffolds suggests that some of the freshwater PRs are found in freshwater Flavobacteria and freshwater SAR11-like bacteria