Investigation of Endophytic Bacterial Community in Supposedly Axenic Cultures of Pineapple and Orchids with Evidence on Abundant Intracellular Bacteria

Abstract

Asepsis, defined as the absence of microbial contamination, is one of the most important requirements of plant micropropagation. In long-term micropropagated cultures, there may occasionally occur scattered microorganism growth in the culture medium. These microorganisms are common plant components and are known as latent endophytes. Thus, the aim of this research was to investigate the presence of endophytic bacteria in asymptomatic pineapple and orchid microplants, which were cultivated in three laboratories for 1 year. Isolation and characterization of bacterial isolates, PCR-DGGE from total genomic DNA of microplants and ultrastructural analysis of leaves were performed. In the culture-dependent technique, it was only possible to obtain bacterial isolates from pineapple microplants. In this case, the bacteria genera identified in the isolation technique were Bacillus, Acinetobacter, and Methylobacterium. The scanning electron microscopy and transmission electron microscopy (SEM and TEM) analyses revealed the presence of endophytic bacteria in intracellular spaces in the leaves of pineapple and orchid microplants, independent of the laboratory or cultivation protocol. Our results strongly indicate that there are endophytic bacterial communities inhabiting the microplants before initiation of the in vitro culture and that some of these endophytes persist in their latent form and can also grow in the culture medium even after long-term micropropagation, thus discarding the concept of "truly axenic plants."

The Effect of Plant Geographical Location and Developmental Stage on Root-Associated Microbiomes of Gymnadenia conopsea

“…However, the result of bacterial microbiome was different from the study of other plant, such as rice (Edwards et al, 2015), Arabidopsis (Duran et al, 2018), millet (Jin et al, 2017), Cycas panzhihuaensis (Zheng and Gong, 2019), which suggested that the compartment was the main factor shaping the composition of the bacterial microbiome. It may relate to the growth characteristics of orchids, which fully or partially relies on mycorrhizal fungi for requisite nutrients; meanwhile, some bacteria, such as the mycorrhiza helper bacteria (MHB) were found to be commonly occurring in ectomycorrhiza and in arbuscular mycorriza associations, which assist mycorrhiza formation (Frey-Klett and Garbaye, 2005;Faria et al, 2013;Esposito-Polesi et al, 2017;Li et al, 2017). Nonetheless, very little is known about the composition, structure, and functional activity of bacterial microbiome associated with orchid, let alone the information in G. conopsea.…”

The preservation effect of Metschnikowia pulcherrima yeast on anthracnose of postharvest mango fruits and the possible mechanism

“…Each data point represents a mean ± standard error (n = 3). Vertical bars on symbols represent ± SE of the mean the yeast became the dominant microorganism at the wound and adapted to the environment of the wound, and the pathogens lost the ability to seize space, the anthracnose pathogens gradually died because there was no growth space [32]. Therefore, competition for nutrition and space became one of the effective ways for the antagonistic yeast M. pulcherrimato inhibiting C. gloeosporioides.…”

Endophytic Bacillus and Pseudomonas spp. Modulate Apple Shoot Growth, Cellular Redox Balance, and Protein Expression Under in Vitro Conditions

“…However, several studies have shown that bacterial endophytes are common in plant tissues grown in vitro and that their beneficial effects on plant growth indicate that they may be useful as growth-promoting agents. In previous studies, a succession of bacterial communities that colonized pineapple microplant organs in vitro were characterized ( Abreu-Tarazi et al, 2010 ) Similarly, endophytic bacteria were isolated from strawberry tissues cultivated in vitro ( Kukkurainen et al, 2005 ; Dias et al, 2009 ), and their beneficial effect on the acclimatization of the seedlings under greenhouse conditions was demonstrated ( Dias et al, 2009 ). Recently, the effects of bacterial endophytes in different in vitro culture phases and in different plant organs of Prunus avium were studied; isolates of the endophytes Rhodopseudomonas palustris and Microbacterium testaceum promoted rooting in two difficult-to-propagate genotypes ( Quambusch et al, 2016 ).…”