Isolation, characterization and plant growth promotion effects of putative bacterial endophytes associated with sweet sorghum (Sorghum bicolor (L) Moench)

Antimicrobial resistance in plant endophytes associated with poultry-manure application revealed by selective culture and whole genome sequencing

Poultry manure is widely used as organic fertilizer in agriculture during the cultivation of crops, but the persistent high-level use of antibiotics in poultry production has raised concerns about the selection for reservoirs of antimicrobial resistance genes (ARGs). Previous studies have shown that the addition of poultry manure can increase the abundance of genes associated with resistance to tetracyclines, aminoglycosides, fluoroquinolones, sulfonamides, bacitracin, chloramphenicol, and macrolide-lincosamide-streptogramin in soil and plants. Understanding the microbial populations that harbor these ARGs is important to identify microorganisms that could enter the human food chain. Here, we test the hypothesis that environmental exposure to poultry manure increases the occurrence of antimicrobial resistance (AMR) in plant endophytes using selective culture, phenotypic Antibiotic Susceptibility Testing (AST), phylogenetic analysis, and whole genome sequencing (WGS). Endophytes from poultry manure treated Sorghum bicolor (L.) Moench plant root and stem samples showed increased phenotypic and genotypic resistance against multiple antibiotics compared to untreated controls. Comparison of AMR phenotype-to-genotype relationships highlighted the detection of multi-drug resistant (MDR) plant endophytes, demonstrating the value of genomic surveillance for emerging drug-resistant pathogens. The increased occurrence of ARGs in poultry manure-exposed endophytes highlights the need for responsible antibiotic use in poultry and animal farming to reduce contamination of ecological niches and transgression into endophytic plant microbiome compartments. It also emphasizes the requirement for proper manure management practices and vigilance in monitoring and surveillance efforts to tackle the growing problem of antibiotic resistance and preserve the efficacy of antibiotics for human and veterinary medicine.

Endophytic Seed-Associated Bacteria as Plant Growth Promoters of Cuban Rice (Oryza sativa L.)

Cuban rice cultivars INCA LP-5 and INCA LP-7 are widely distributed in Cuba and Caribbean countries. Although there are studies about rhizospheric bacteria associated with these cultivars, there are no reports about their seed-associated bacteria. This study aimed to isolate endophytic bacteria from rice seeds and select those with the greatest plant growth-promoting traits. A total of nineteen bacterial strains from the genera Pantoea, Bacillus, Paenibacillus, and Pseudomonas were isolated from the husk and endosperm of rice seeds. The strains Pantoea sp. S5-1, Pseudomonas sp. S5-38, and Pseudomonas sp. S7-1 were classified as the most promissory to increase rice growth as they demonstrated the presence of multiple plant growth-promoting traits such as the production of auxins, phosphate, and potassium solubilization, the production of siderophores, and the inhibition of the phytopathogen Pyricularia oryzae. The inoculation of strains of Pantoea sp. and Pseudomonas spp. in rice improves the height, root length, fresh weight, and dry weight of the shoot and root after 21 days post-inoculation in hydroponic assays. This study constitutes the first report on Cuban rice cultivars about the presence of endophytes in seeds and their potential to promote seedling growth. Pantoea sp. S5-1, Pseudomonas sp. S5-38, and Pseudomonas sp. S7-1 were selected as the more promising strains for the development of bio-stimulators or bio-inoculants for Cuban rice crops.

Resistome profiling reveals transmission dynamics of antimicrobial resistance genes from poultry litter to soil and plant

Poultry farming is a major livelihood in South and Southeast Asian economies where it is undergoing rapid intensification to meet the growing human demand for dietary protein. Intensification of poultry production systems is commonly supported by increased antimicrobial drug use, risking greater selection and dissemination of antimicrobial resistance genes (ARGs). Transmission of ARGs through food chains is an emerging threat. Here, we investigated transmission of ARGs from chicken (broiler and layer) litter to soil and Sorghum bicolor (L.) Moench plants based on field and pot experiments. The results demonstrate ARGs transmission from poultry litter to plant systems under field as well as experimental pot conditions. The most common ARGs could be tracked for transmission from litter to soil to plants were identified as detected were cmx, ErmX, ErmF, lnuB, TEM-98 and TEM-99, while common microorganisms included Escherichia coli, Staphylococcus aureus, Enterococcus faecium, Pseudomonas aeruginosa, and Vibrio cholerae. Using next generation sequencing and digital PCR assays we detected ARGs transmitted from poultry litter in both the roots and stems of S. bicolor (L.) Moench plants. Poultry litter is frequently used as a fertiliser because of its high nitrogen content; our studies show that ARGs can transmit from litter to plants and illustrates the risks posed to the environment by antimicrobial treatment of poultry. This knowledge is useful for formulating intervention strategies that can reduce or prevent ARGs transmission from one value chain to another, improving understanding of impacts on human and environmental health. The research outcome will help in further understanding the transmission and risks posed by ARGs from poultry to environmental and human/animal health.

Replacement of water yam (Dioscorea alata L.) indigenous root endophytes and rhizosphere bacterial communities via inoculation with a synthetic bacterial community of dominant nitrogen-fixing bacteria

Biofertilizers containing high-density plant growth-promoting bacteria are gaining interest as a sustainable solution to environmental problems caused by eutrophication. However, owing to the limitations of current investigative techniques, the selected microorganisms are not always preferred by the host plant, preventing recruitment into the native microbiota or failing to induce plant growth-promoting effects. To address this, five nitrogen-fixing bacteria previously isolated from water yam (Dioscorea alata L.) plants and showing dominant abundance of 1% or more in the water yam microbiota were selected for analysis of their plant growth-promoting activities when used as a synthetic bacterial inoculant. Water yam cv. A-19 plants were inoculated twice at 10 and 12 weeks after planting under greenhouse conditions. Bacterial communities in root, rhizosphere, and bulk soil samples were characterized using high-throughput 16S rRNA amplicon sequencing. Compared with non-inoculated plants, all bacterial communities were significantly altered by inoculation, mainly at the genus level. The inoculation effects were apparently found in the root communities at 16 weeks after planting, with all inoculated genera showing dominance (in the top 35 genera) compared with the control samples. However, no significant differences in any of the growth parameters or nitrogen contents were observed between treatments. At 20 weeks after planting, the dominance of Stenotrophomonas in the inoculated roots decreased, indicating a decline in the inoculation effects. Interestingly, only the Allorhizobium-Neorhizobium-Pararhizobium-Rhizobium clade was dominant (>1% relative abundance) across all samples, suggesting that bacteria related to this clade are essential core bacteria for water yam growth. This is the first report on addition of a synthetic nitrogen-fixing bacterial community in water yam plants showing that native bacterial communities can be replaced by a synthetic bacterial community, with declining in the effects of Stenotrophomonas on the modified communities several weeks after inoculation.

Isolation, characterization and plant growth-promoting effects of sorghum [Sorghum bicolor (L.) moench] root-associated rhizobacteria and their potential role in drought mitigation

Drought is a major constraint throughout the world, and it creates a major yield loss by changing the plant metabolic process. However, the negative effects of drought on plant growth and development were alleviated by using plant growth-promoting bacteria. With these backgrounds, the study was conducted to identify the drought-tolerant endophytic bacteria and to know their plant growth promotion (PGP) effect on sorghum plants under drought conditions. From sorghum root, Acinetobacter pittii, Bacillus lichiniformis, Bacillus sp., Pseudacidovorax intermedius, and Acinetobacter baumannii strains were isolated and identified through 16S rRNA sequencing. These strains had higher levels of proline, protein, exopolysaccharides (EPS), 1-aminocyclopropane-l-carboxylic acid (ACC) deaminase, indole-3-Acetic Acid (IAA), and gibberellic acid (GA). An experiment was carried out in the laboratory to evaluate the effects of three drought-tolerant strains, A. pittii, Bacillus sp., and P. intermedius, on the growth of sorghum seedlings. Whereas root length (RL), shoot length (SL), seedling vigor index (SVI), and total dry matter production (TDM) were more in the Bacillus sp., and P. intermedius inoculated plants in both stress and non-stress condition. Principle component analysis revealed that Bacillus sp. and P. intermedius improved the growth characteristics and protect the seedling from water stress situations. A correlation study between the variables showed a positive significant correlation between all variables except root: shoot ratio (RSR) and SL. Variable RSR was not significantly correlated with GP, GRI, and SL; SVI and TDM showed a non-significant correlation with RSR.

Aluminum-tolerant, growth-promoting endophytic bacteria as contributors in promoting tea plant growth and alleviating aluminum stress

Unlike that of other crops, the growth of tea plants can be promoted by aluminum, but its regulation mechanism remains unclear. Some endophytes can also promote growth of plant hosts. In this paper, tea roots treated with aluminum were used to study the growth-promoting traits and aluminum tolerance of endophytes. Meta-16S rDNA analysis revealed that Burkholderia was enriched in tea roots after aluminum treatment, and it was the dominant strain for hydroponic tea roots and field tea roots. Actinomycetes constituted the dominant strains in hydroponic tea seedlings treated with aluminum. Sixteen endophytic bacteria, including 12 strains of Firmicutes, 2 strains of Proteobacteria and 2 strains of Actinomycetes, were isolated and identified from hydroponic tea roots treated with different aluminum concentrations. Growth-promoting activity analysis showed that the isolated endophytic bacteria all had more than one plant growth-promoting trait. Among them, B4 (Bacillus nealsonii), B8 (Brevibacterium frigoritolerans) and A2 (Nocardia nova) bacteria each had three growth-promoting traits. Aluminum tolerance ability analysis indicated that endophyte A1 (Leifsonia shinshuensis) had the strongest aluminum tolerance ability, up to 200 mg l-1 aluminum. Plant-bacteria interactions showed that endophytes A1, A2 and B4 and their synthetic community all had a growth-promoting effect on the growth of wheat lateral roots. Moreover, endophytes A1 and B4 alleviated aluminum stress in wheat. Endophyte A1 also promoted the growth of tea cuttings, especially lateral roots, with/without aluminum. Taken together, aluminum enhanced the distribution of aluminum-tolerant and growth-promoting bacteria, thereby promoting the growth of tea roots. This study provides a new aspect for research on the mechanism by which aluminum promotes tea plant growth.

Effects of organic materials on soil bacterial community structure in long-term continuous cropping of tomato in greenhouse

Long-term fertilization will affect the above-ground vegetation, but we have little understanding of soil bacterial community structure and diversity so far. This study aims to study the effect of organic fertilization on the soil bacterial community structure and diversity of protected long-term continuous tomato cropping by using high-throughput sequencing technology. Results show that (1) fertilization application (chemical fertilizer [CF] and vermicompost [VM]) significantly changed the soil physico-chemistry properties, such as soil pH decreased compared with control treatment and increased the soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), and total potassium (TK) contents; (2) VM increased the Shannon index of soil bacteria but decreased the soil Chao1 index; and (3) soil Proteobacteria and Actinomycetes were dominant taxa and the relative abundance of Actinobacteria increased by 36.40–44.27 and 25.80–29.35%, with CF and VM, respectively, compared with the control. Pearson correlation analysis showed that soil pH, SOC, TN, TP, and TK were the main environmental factors that affected the diversity and richness of soil bacterial communities. Redundancy analysis (RDA) showed that the SOC and TN play important roles in the composition of soil bacterial communities. In summary, the effect of VM on the soil bacterial community structure of continuous tomato cropping is better than that of CF, which should be used in the sustainable production of facility tomatoes.

Paenibacillus sp. Strain UY79, Isolated from a Root Nodule of Arachis villosa, Displays a Broad Spectrum of Antifungal Activity

A nodule-inhabiting Paenibacillus sp. strain (UY79) isolated from wild peanut (Arachis villosa) was screened for its antagonistic activity against diverse fungi and oomycetes (Botrytis cinerea, Fusarium verticillioides, Fusarium oxysporum, Fusarium graminearum, Fusarium semitectum, Macrophomina phaseolina, Phomopsis longicolla, Pythium ultimum, Phytophthora sojae, Rhizoctonia solani, Sclerotium rolfsii, and Trichoderma atroviride). The results obtained show that Paenibacillus sp. UY79 was able to antagonize these fungi/oomycetes and that agar-diffusible compounds and volatile compounds (different from HCN) participate in the antagonism exerted. Acetoin, 2,3-butanediol, and 2-methyl-1-butanol were identified among the volatile compounds produced by strain UY79 with possible antagonistic activity against fungi/oomycetes. Paenibacillus sp. strain UY79 did not affect symbiotic association or growth promotion of alfalfa plants when coinoculated with rhizobia. By whole-genome sequence analysis, we determined that strain UY79 is a new species of Paenibacillus within the Paenibacillus polymyxa complex. Diverse genes putatively involved in biocontrol activity were identified in the UY79 genome. Furthermore, according to genome mining and antibiosis assays, strain UY79 would have the capability to modulate the growth of bacteria commonly found in soil/plant communities. IMPORTANCE Phytopathogenic fungi and oomycetes are responsible for causing devastating losses in agricultural crops. Therefore, there is enormous interest in the development of effective and complementary strategies that allow the control of the phytopathogens, reducing the input of agrochemicals in croplands. The discovery of new strains with expanded antifungal activities and with a broad spectrum of action is challenging and of great future impact. Diverse strains belonging to the P. polymyxa complex have been reported to be effective biocontrol agents. Results presented here show that the novel discovered strain of Paenibacillus sp. presents diverse traits involved in antagonistic activity against a broad spectrum of pathogens and is a potential and valuable strain to be further assessed for the development of biofungicides.

Sorghum-Phosphate Solubilizers Interactions: Crop Nutrition, Biotic Stress Alleviation, and Yield Optimization

Sweet sorghum [Sorghum bicolor (L.) Moench] is a highly productive, gluten-free cereal crop plant that can be used as an alternative energy resource, human food, and livestock feed or for biofuel-ethanol production. Phosphate fertilization is a common practice to optimize sorghum yield but because of high cost, environmental hazards, and soil fertility reduction, the use of chemical P fertilizer is discouraged. Due to this, the impetus to search for an inexpensive and eco-friendly microbiome as an alternative to chemical P biofertilizer has been increased. Microbial formulations, especially phosphate solubilizing microbiome (PSM) either alone or in synergism with other rhizobacteria, modify the soil nutrient pool and augment the growth, P nutrition, and yield of sorghum. The use of PSM in sorghum disease management reduces the dependence on pesticides employed to control the phytopathogens damage. The role of PSM in the sorghum cultivation system is, however, relatively unresearched. In this manuscript, the diversity and the strategies adopted by PSM to expedite sorghum yield are reviewed, including the nutritional importance of sorghum in human health and the mechanism of P solubilization by PSM. Also, the impact of solo or composite inoculations of biological enhancers (PSM) with nitrogen fixers or arbuscular mycorrhizal fungi is explained. The approaches employed by PSM to control sorghum phytopathogens are highlighted. The simultaneous bio-enhancing and biocontrol activity of the PS microbiome provides better options for the replacement of chemical P fertilizers and pesticide application in sustainable sorghum production practices.

Interaction among endophytic bacteria, sweet sorghum (Sorghum bicolor) cultivars and chemical nitrogen fertilization

The application of new agricultural technologies to attain sustainable production systems is necessary. The use of plant growth-promoting bacteria to improve plant growth and health has been studied for decades. This work aimed to isolate diazotrophic endophytic bacteria associated with sweet sorghum plants and study the interaction of their inoculation in combination with chemical N-fertilization on different sorghum cultivars. A bacterial collection of 181 isolates was constructed and characterized in vitro and in vivo. From that, the strains Enterobacter sp. UYSB89 and Kosakonia sp. UYSB139 were nifH+, produce IAA, defined as true endophytes and able to promote growth of two sweet sorghum under greenhouse conditions. The evaluated cultivars responded differentially to bacterial inoculation, the nitrogen fertilization doses and their interaction. Thus, plant growth is a multifactorial consequence of the interrelation between crop practices and the plant genotypes. This knowledge is a valuable factor in terms of understanding plant-bacteria endophyte interactions to preserve environmental sustainability during the implementation of agronomic practices.

The endosphere microbial communities, a great promise in agriculture

Agricultural food production and sustainability need intensification to address the current global food supply to meet human demand. The continuous human population increase and other anthropogenic activities threaten food security. Agrochemical inputs have long been used in conventional agricultural systems to boost crop productivity, but they are disadvantageous to a safe environment. Towards developing environmentally friendly agriculture, efforts are being directed in exploring biological resources from soil and plant microbes. The survival of the rhizosphere and endosphere microbiota is influenced by biotic and abiotic factors. Plant microbiota live interdependently with the host plants. Endophytes are regarded as colonizer microbes inhabiting and establishing microbial communities within the plant tissue. Their activities are varied and include fixing atmospheric nitrogen, solubilizing phosphate, synthesis of siderophores, secretion of metabolite-like compounds containing active biocontrol agents in the control of phytopathogens, and induced systemic resistance that stimulates plant response to withstand stress. Exploring beneficial endophyte resources in the formulation of bio-inoculants, such as biofertilizers, as an alternative to agrochemicals (fertilizers and pesticides) in developing environmentally friendly agriculture and for incorporation into crop breeding and disease control program is promising. Therefore, in this review, endosphere microbial ecology, associating environmental factors, and their roles that contribute to their effectiveness in promoting plant growth for maximum agricultural crop productivity were highlighted.

Drought-tolerant and plant growth-promoting endophytic Staphylococcus sp. having synergistic effect with silicate supplementation

Endophytic bacteria have been reported to have symbiotic, mutualistic, commensalistic or trophobiotic relationships with various plant parts. As part of its adaptation, many endophytic organisms are known to exhibit properties with multiple beneficial effects to the plant system. Even though many bacterial genera have been identified to have endophytic association, isolation of those which were previously demonstrated well for human association is quite interesting. In the study, endophytic bacteria Ceb1 isolated from the rhizome of Curcuma longa was identified by 16S rDNA sequencing as Staphylococcus sp. Further, Ceb1 was observed to have the ability to tolerate drought stress. While screening for the plant growth-promoting traits, Ceb1 was found to be positive for IAA production both under drought-stressed and normal conditions as confirmed by HPLC. The Ceb1 priming with Vigna unguiculata was observed to enhance the growth parameters of the plant. Analysis of Ceb1-treated plants by ICP-MS further showed modulation of both macro- and micronutrients. Upon drought stress induction in Vigna unguiculata, Ceb1 was found to provide synergistic plant growth-promoting effect to the plant along with the supplemented silicate sources. Under the changing agroclimatic conditions, exploring the plant stress-alleviating effects of endophytes is highly significant.

Culturable endophytic bacteria of Camellia species endowed with plant growth promoting characteristics

AIM

Tea (Camellia sinensis (L.) O. Kuntze) is an economically important caffeine-containing beverage crop with massive plantation in the Northeast corner of the agroclimatic belt of India. The main aim of the work was to isolate, identify and characterize the native plant growth promoting endophytes associated with tea for future microbe based bioformulation.

METHODS AND RESULTS

A total of 129 endophytic bacteria were isolated and characterized for plant growth promoting traits such as indole-3-acetic acid (IAA), phosphate solubilization, ammonia production, biocontrol traits like siderophore and extracellular enzyme production. BOX-PCR fingerprinting was used to differentiate the various bacterial isolates obtained from six different tea species. 16S rRNA sequencing and blast analysis showed that these isolates belonged to different genera, that is, Bacillus, Brevibacterium, Paenibacillus and Lysinibacillus. Lysinibacillus sp. S24 showed the highest phosphate solubilization and IAA acid production efficiency of 268·4 ± 14·3 and 13·5 ± 0·5 µg ml^-1 , respectively. Brevibacterium sp. S91 showed the highest ammonia production of 6·2 ± 0·5 µmol ml^-1 . Chitinase, cellulase, protease and pectinase activities were shown by 4·6, 34·1, 27·13 and 13·14% of the total isolates, respectively. Similarly, 41% of the total isolates were positive for 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase activity. Further, the potent PGP isolates, S24 and S91 were able to enhance the vegetative parameters such as dry/fresh weight of root and shoot of tea plants in nursery conditions.

CONCLUSION

Our findings corroborate that tea endophytic bacteria possess the potential to demonstrate multiple PGP traits both, in vivo and in vitro and have the potential for further large-scale trials.

SIGNIFICANCE AND IMPACT OF THE STUDY

The exploration of tea endophytic bacterial community is suitable for the development of bioformulations for an integrated nutrient management and thus sustainable crop production and decreasing the hazardous effects of chemical fertilizers on the environment and human health.

The Endophytic Bacterial Microbiota Associated with Sweet Sorghum (Sorghum bicolor) Is Modulated by the Application of Chemical N Fertilizer to the Field

Sweet sorghum (Sorghum bicolor) is a multipurpose crop used as a feedstock to produce bioethanol, sugar, energy, and animal feed. However, it requires high levels of N fertilizer application to achieve the optimal growth, which causes environmental degradation. Bacterial endophytes, which live inside plant tissues, play a key role in the health and productivity of their host. This particular community may be influenced by different agronomical practices. The aim of the work was to evaluate the effects of N fertilization on the structure, diversity, abundance, and composition of endophytic and diazotrophic bacterial community associated with field-grown sweet sorghum. PCR-DGGE, quantitative PCR, and high-throughput sequencing were performed based on the amplification of rrs and nifH genes. The level of N fertilization affected the structure and abundance but not the diversity of the endophytic bacterial communities associated with sweet sorghum plants. This effect was pronounced in the roots of both bacterial communities analyzed and may depend on the physiological state of the plants. Specific bacterial classes and genera increased or decreased when the fertilizer was applied. The data obtained here contribute to a better understanding on the effects of agronomical practices on the microbiota associated with this important crop, with the aim to improve its sustainability.

Culturable Endophytic Bacteria of Ginger Rhizome and their Remarkable Multi-trait Plant Growth-Promoting Features

Functional contribution of endophytic bacteria towards plant growth is highly impressive due to their species diversity and array of probiotic mechanisms. In the study, 96 endophytic bacteria isolated from rhizome of ginger (Zingiber officinale) were screened for phosphate solubilisation, 1-amino cyclopropane-1-carboxylate (ACC) deaminase activity, nitrogen fixation, ammonia and IAA production. Among these, sixteen endophytes with multiple plant growth-promoting activities were identified by 16S rDNA sequencing and all of them showed growth enhancement in Vigna unguiculata var Lola which make the study remarkably significant. The result was a clear indication of consistent, reliable and broad spectrum plant probiotic features of all the selected isolates. However, strain-specific effects on soil parameters represent the unique and distinguishable role of each of the selected isolates in the chemobiology of ginger rhizome. The study provided deeper insight into microbiomics of ginger rhizome with its agricultural promises.

A Culture-Independent Approach to Enrich Endophytic Bacterial Cells from Sugarcane Stems for Community Characterization

Bacterial endophytes constitute a very diverse community and they confer important benefits which help to improve agricultural yield. Some of these benefits remain underexplored or little understood, mainly due to the bottlenecks associated with the plant feature, a low number of endophytic bacterial cells in relation to the plant, and difficulties in accessing these bacteria using cultivation-independent methods. Enriching endophytic bacterial cells from plant tissues, based on a non-biased, cultivation-independent physical enrichment method, may help to circumvent those problems, especially in the case of sugarcane stems, which have a high degree of interfering factors, such as polysaccharides, phenolic compounds, nucleases, and fibers. In the present study, an enrichment approach for endophytic bacterial cells from sugarcane lower stems is described. The results demonstrate that the enriched bacterial cells are suitable for endophytic community characterization. A community analysis revealed the presence of previously well-described but also novel endophytic bacteria in sugarcane tissues which may exert functions such as plant growth promotion and biological control, with a predominance of the Proteobacterial phylum, but also Actinobacteria, Bacteroidetes, and Firmicutes, among others. In addition, by comparing the present and literature data, it was possible to list the most frequently detected bacterial endophyte genera in sugarcane tissues. The presented enrichment approach paves the way for improved future research toward the assessment of endophytic bacterial community in sugarcane and other biofuel crops.

Colonization study of gfp-tagged Achromobacter marplatensis strain in sugar beet

This study details the introduction of a gfp marker into an endophytic bacterial strain (Achromobacter marplatensis strain 17, isolated from sugar beet) to monitor its colonization of sugar beet (Beta. vulgaris L.). Stability of the plasmid encoding the gfp was confirmed in vitro for at least 72 h of bacterial growth and after the colonization of tissues, under nonselective conditions. The colonization was observed using fluorescence microscopy and enumeration of culturable endophytes in inoculated sugar beet plants that grew for 10 or 20 days. gfp-Expressing strains were re-isolated from the inner tissues of surface-sterilized roots and stems of inoculated plants, and the survival of the Achromobacter marplatensis 17:gfp strain in plants 20 days after inoculation, even in the absence of selective pressure, suggests that it is good colonizer. These results also suggest that this strain could be a useful tool for the delivery of enzymes or other proteins into plants. In addition, the study highlights that sugar beet plants can be used effectively for detailed in vitro studies on the interactions between A. marplatensis strain 17 and its host, particularly if a gfp-tagged strain of the pathogen is used.