Salmonella spp. is a facultative intracellular pathogen causing localized or systemic infections, involving economic and public health significance, and remains the leading pathogen of food safety concern worldwide, with poultry being the primary transmission vector. Antibiotics have been the main strategy for Salmonella control for many years, which has allowed producers to improve the growth and health of food-producing animals. However, the utilization of antibiotics has been reconsidered since bacterial pathogens have established and shared a variety of antibiotic resistance mechanisms that can quickly increase within microbial communities. The use of alternatives to antibiotics has been recommended and successfully applied in many countries, leading to the core aim of this review, focused on (1) describing the importance of Salmonella infection in poultry and the effects associated with the use of antibiotics for disease control; (2) discussing the use of feeding-based (prebiotics, probiotics, bacterial subproducts, phytobiotics) and non-feeding-based (bacteriophages, in ovo injection, vaccines) strategies in poultry production for Salmonella control; and (3) exploring the use of complementary strategies, highlighting those based on -omics tools, to assess the effects of using the available antibiotic-free alternatives and their role in lowering dependency on the existing antimicrobial substances to manage bacterial infections in poultry effectively.

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24The free-living soil bacteria that are beneficial for the growth of plants are known as 25 plant growth-promoting rhizobacteria (PGPR). In this work, a multi-species of PGPR 26 bacteria inoculant was designed, which included nitrogen-fixing strains such as 27 Rhizobium phaseoli, Sinorhizobium americanum and Azospirillum brasilense, as well as 28 other plant growth promoting bacteria such as Bacillus subtillis and Methylobacterium 29 extorquens. The multi-species community exerted a beneficial effect on plant seedlings 30 when it was inoculated, greater than the effect observed when inoculating each bacteria 31 individually. Acetylene reduction of maize roots was recorded with the multi-species 32 inoculant, which suggests that nitrogen fixation occurred under these conditions. To 33 analyze the contributions of the different nitrogen-fixing bacteria that were inoculated, a 34 metatranscriptomic analysis was performed. The differential expression analysis 35 revealed that the predominantly nif transcripts of Azospirillum are overexpressed, 36 suggesting that it was responsible for nitrogen fixation in maize. Overall, we analyzed 37 the interaction of a synthetic community, suggesting it as an option, for future 38 formulations of biofertilizers. 39 IMPORTANCE 40While nodulation processes and nitrogen fixation by rhizobia have been well studied, 41 little is known about the interaction between rhizobia and non-leguminous plants such 42 as maize, which is used as a model for this study. Nitrogen fixation in cereals is a long 43 searched goal. Instead of single species inoculants, multi-species inoculation may be 44 more efficient to promote plant growth and fix nitrogen. Metatrascriptomes allowed us 45 to recognize the bacteria responsible for nitrogen fixation in plant rootlets. The study of 46 the function of certain genes may help to understand how microorganisms interact with 47 3 the root plant, as well as allow a better use of microorganisms for the generation of 48 novel biofertilizers using microbial consortia. 49 INTRODUCTION 50 In nature and in agricultural fields there is a large diversity of bacteria associated with 51 plants. Once isolated in culture media and subsequently tested individually in plant 52 assays, many plant-bacteria prove to be capable of promoting plant growth. Bacterial 53 mechanisms of action are diverse, and some bacteria may exhibit more than one 54 mechanism. Plant growth promoting rhizobacteria (PGPR) may produce phytohormones 55 or volatiles, solubilize nutrients, fix nitrogen or inhibit pests/pathogens. Among them, 56 nitrogen-fixing bacteria are in general a minority, possibly due to the metabolic charge 57 of fixing nitrogen. 58 As bacteria are not alone in soil and in plants, recent inoculation assays have considered 59 the use of more than single strains, and combinations of Azospirillum and rhizobia or 60 Bacillus and rhizobia have been more successful than single-strain inoculants in 61 promoting plant growth (reviewd in 1-3). For example, Azospirillum and 62 Br...

Bacteria have been used to increase crop yields. For their application on crops, bacteria are provided in inoculant formulations that are continuously changing, with liquid- and solid-based products. Bacteria for inoculants are mainly selected from natural isolates. In nature, microorganisms that favor plants exhibit various strategies to succeed and prevail in the rhizosphere, such as biological nitrogen fixation, phosphorus solubilization, and siderophore production. On the other hand, plants have strategies to maintain beneficial microorganisms, such as the exudation of chemoattractanst for specific microorganisms and signaling pathways that regulate plant–bacteria interactions. Transcriptomic approaches are helpful in attempting to elucidate plant–microorganism interactions. Here, we present a review of these issues.

The poultry industry is constantly demanding novel strategies to improve the productivity and health status of hens, prioritizing those based on the holistic use of natural resources. This study aimed to assess the effects of an Allium-based phytobiotic on productivity, egg quality, and fecal microbiota of laying hens. One hundred and ninety-two 14-week-old Lohmann Lite LSL hens were allocated into an experimental farm, fed with a commercial concentrate with and without the Allium-based phytobiotic, and challenged against Salmonella. Productivity, egg quality, and fecal microbiota were monitored for 20 weeks. Results showed that the phytobiotic caused an increase on the number of eggs laid (p < 0.05) and in the feed conversion rate (p < 0.05); meanwhile, egg quality, expressed as egg weight, albumin height, haugh units, egg shell strength, and egg shell thickness remained unchanged (p > 0.05), although yolk color was decreased. Fecal microbiota structure was also modified, indicating a modulation of the gut microbiota by increasing the presence of Firmicutes and Bacteroidetes but reducing Proteobacteria and Actinobacteria phyla. Predicted changes in the functional profiles of fecal microbiota suggest alterations in metabolic activities that could be responsible for the improvement and maintenance of productivity and egg quality when the phytobiotic was supplemented; thus, Allium-based phytobiotic has a major impact on the performance of laying hens associated with a possible gut microbiota modulation.

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