Bacterial Communities Associated with Surfaces of Leafy Greens: Shift in Composition and Decrease in Richness over Time

Abstract

The phyllosphere is colonized by a wide variety of bacteria and fungi; it harbors epiphytes, as well as plant-pathogenic bacteria and even human pathogens. However, little is known about how the bacterial community composition on leafy greens develops over time. The bacterial community of the leafy-green phyllosphere obtained from two plantings of rocket salad (Diplotaxis tenuifolia) and three plantings of lettuce (Lactuca sativa) at two farms in Norway were profiled by an Illumina MiSeq-based approach. We found that the bacterial richness of the L. sativa samples was significantly greater shortly (3 weeks) after planting than at harvest (5 to 7 weeks after planting) for plantings 1 and 3 at both farms. For the second planting, the bacterial diversity remained consistent at the two sites. This suggests that the effect on bacterial colonization of leaves, at least in part must, be seasonally driven rather than driven solely by leaf maturity. The distribution of phyllosphere communities varied between D. tenuifolia and L. sativa at harvest. The variability between these species at the same location suggests that the leaf-dwelling bacteria are not only passive inhabitants but interact with the host, which shapes niches favoring the growth of particular taxa. This work contributes to our understanding of host plant-specific microbial community structures and shows how these communities change throughout plant development.T he phyllosphere is a habitat on the surface of plant leaves colonized by a variety of bacteria, yeasts, and fungi (1). It harbors epiphytes, as well as plant-pathogenic bacteria and even human pathogens. Microbial populations on leaf surfaces are highly influenced by rapid fluctuations in UV radiation, temperature, and humidity and are restricted by limited access to nutrients (1, 2). Resident bacteria on leaves can have neutral, negative, or positive influences on their host plants by serving as pathogens, preventing leaf colonization by pathogens, or acting as growth promoters (3). Traditionally, phyllosphere bacteria have been characterized by using culture-based approaches and much of the work on produce-associated bacteria has focused on a small number of pathogenic species. Culture-based methods will not include bacteria that are not able to grow on standard artificial media or are slow growing. This limits our understanding of the phyllosphere microbial community's ecology, genetics, and physiology (4). Bacterial communities associated with leafy greens have already been described by several culture-independent studies. "First-generation" molecular techniques have been used to describe variation in community structure in the context of leaf surface properties and microbial interactions (5), seasonal variation in the community structure (6), and monitoring of bacterial communities in the food chain (7). The introduction of culture-independent methods, in particular, microbial profiling using high-throughput sequencing to study microorganisms, has revealed more complexity and diversity of the...

Complete genome sequence of the biofilm-forming Curtobacterium sp. strain BH-2-1-1, isolated from lettuce ( Lactuca sativa ) originating from a conventional field in Norway

“…A yellow-pigmented biofilm-forming Curteobacterium sp. strain BH-2-1-1 was isolated from the leaf surface of conventionally grown lettuce ( Lactuca sativa ) in Vestfold, Norway [5]. Genomic DNA was extracted using Genomic-tip 500/G kit (Qiagen GmbH, Hilden, Germany), a library was created using PacBio (Pacific Biosciences, California, USA) 20 kb library preparation protocol and whole genome sequencing was performed using PacBio RS II.…”

Plant species affects establishment ofEscherichia coliO157:H7gfp+on leafy vegetables

“…; Dees et al . ) and that plant cultivar may have an impact on colonization by human pathogens (Klerks et al . ; Quilliam et al .…”

“…; Dees et al . ). The indigenous microbiota, which is well adapted to the environmental conditions on the leaf surface, can have an impact on immigrant bacteria such as human pathogens (Monier and Lindow ; Poza‐Carrion et al .…”

Complete genome sequence of the biofilm-forming Microbacterium sp. strain BH-3-3-3, isolated from conventional field-grown lettuce ( Lactuca sativa ) in Norway

“…An orange-pigmented Microbacterium sp. strain (BH-3-3-3) was isolated from the leaf surface of lettuce ( Lactuca sativa ) originating from a conventional field in Vestfold, Norway [5]. Genomic DNA was extracted using Genomic-tip 500/G kit (Qiagen GmbH, Hilden, Germany), a library was created using PacBio (Pacific Biosciences, California, USA) 20 kb library preparation protocol and whole genome sequencing was performed using PacBio RS II.…”