Evaluation of environmental bacterial communities as a factor affecting the growth of duckweed Lemna minor

Abstract

BackgroundDuckweed (family Lemnaceae) has recently been recognized as an ideal biomass feedstock for biofuel production due to its rapid growth and high starch content, which inspired interest in improving their productivity. Since microbes that co-exist with plants are known to have significant effects on their growth according to the previous studies for terrestrial plants, this study has attempted to understand the plant–microbial interactions of a duckweed, Lemna minor, focusing on the growth promotion/inhibition effects so as to assess the possibility of accelerated duckweed production by modifying co-existing bacterial community.ResultsCo-cultivation of aseptic L. minor and bacterial communities collected from various aquatic environments resulted in changes in duckweed growth ranging from −24 to +14% compared to aseptic control. A number of bacterial strains were isolated from both growth-promoting and growth-inhibitory communities, and examined for their co-existing effects on duckweed growth. Irrespective of the source, each strain showed promotive, inhibitory, or neutral effects when individually co-cultured with L. minor. To further analyze the interactions among these bacterial strains in a community, binary combinations of promotive and inhibitory strains were co-cultured with aseptic L. minor, resulting in that combinations of promotive–promotive or inhibitory–inhibitory strains generally showed effects similar to those of individual strains. However, combinations of promotive–inhibitory strains tended to show inhibitory effects while only Aquitalea magnusonii H3 exerted its plant growth-promoting effect in all combinations tested.ConclusionSignificant change in biomass production was observed when duckweed was co-cultivated with environmental bacterial communities. Promotive, neutral, and inhibitory bacteria in the community would synergistically determine the effects. The results indicate the possibility of improving duckweed biomass production via regulation of co-existing bacterial communities.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-017-0746-8) contains supplementary material, which is available to authorized users.

Mutualism outcome across plant populations, microbes, and environments in the duckweedLemna minor

“…In plant-microbe mutualisms, we generally see positive correlations between host and symbiont fitness (Friesen, 2012), although some environments may decouple them (Weese et al, 2015; Shantz et al, 2016). Aquatic microbes associated with duckweed species that may affect growth are known to include diatoms (Desianti, 2012), nitrogen-fixing cyanobacteria (Zuberer, 1982; Duong and Tiedje, 1985; Eckardt and Biesboer, 1988), and a collection of additional bacteria, including members of other nitrogen-fixing clades (Underwood and Baker, 1991; Ishizawa et al, 2017b), and one that may provision phosphorus (Ishizawa et al, 2017a). Here we find positive correlations between duckweed fitness and microbial growth across treatments (Figure 3), potentially indicating positive fitness feedbacks (Sachs et al, 2004) between duckweed and the community of microbes that live on them.…”

“…Here, we found that microbiome variation has complex effects on phenotypes and fitness in an aquatic plant, similar to how microbiome variation affects terrestrial plants. This is despite the fact that duckweed draws a microbiome from the water environment that is less complex than typical terrestrial plant microbiomes (Lundberg et al, 2012; Ishizawa et al, 2017b). As a smaller plant with a simpler microbiome, more manipulative experimentation is possible for duckweed microbiomes than for terrestrial plant microbiomes.…”

“…Our current understanding of plant-microbe interactions largely comes from studies of nutritional symbioses in terrestrial plants, such as legume-rhizobium or plant-mycorrhizal associations that alleviate a nutrient stress of the plant. However, plants support a diverse community of microbes on their roots (Bulgarelli et al, 2012; Lundberg et al, 2012; Ishizawa et al, 2017b) that can modulate effects of other plant stressors, including environmental contaminants. Microbes can reduce the impacts of contaminants on plants by preventing contaminants from being taken up, by helping plants tolerate or sequester compounds, or by promoting plant growth in general and simply diluting harm done by the contaminant (Rajkumar et al, 2012).…”

“…It is unclear how much of our understanding of plant-microbe interactions in terrestrial environments translates to floating aquatic habitats. For example, unlike the rhizosphere microbiomes of terrestrial plants, the diversity of species growing with Lemna minor is likely much lower (Ishizawa et al, 2017b). However, there is already some suggestive evidence for GxGxE effects in duckweed-microbiome-contaminant systems, in that microbial communities affect duckweed growth rates and contaminant removal (Zhao et al, 2014b, 2015; Ishizawa et al, 2017b).…”

“…For example, unlike the rhizosphere microbiomes of terrestrial plants, the diversity of species growing with Lemna minor is likely much lower (Ishizawa et al, 2017b). However, there is already some suggestive evidence for GxGxE effects in duckweed-microbiome-contaminant systems, in that microbial communities affect duckweed growth rates and contaminant removal (Zhao et al, 2014b, 2015; Ishizawa et al, 2017b). Here, we explored the interactive effects of microbial communities, zinc contamination, and host genotype on duckweed fitness and phenotypes, as well as on microbial growth.…”