Free-living bacteria that actively colonize plant roots and provide positive effects on plant development are called plant-growth promoting. Plant growth-promoting bacteria can promote plant growth and use their own metabolism to solubilize phosphates, produce hormones and fix nitrogen, and they can directly affect plant metabolism. PGPR also increase plant absorption of water and nutrients, improving root development and increasing plant enzymatic activity; moreover, PGPR can promote other microorganisms as part of a synergistic effect to improve their effects on plants, promoting plant growth or suppressing pathogens. Many studies have shown several benefits of the use of PGPR in maize and sugarcane crops. These bacteria are an excellent alternative to farmers to reduce chemical fertilization and pesticide input without promoting the environment impact and yield-reducing. The present review is an effort to elucidate the concept of rhizobacteria in the current scenario and their underlying mechanisms of plant growth promotion with recent updates. The latest paradigms of a wide range of applications of these beneficial rhizobacteria in both crops maize and sugarcane have been presented explicitly to garner broad perspectives regarding their functioning and applicability. The results from several studies have shown that the utilization of PGPR in maize and sugarcane is the great alternative to farmers face the challenge the modern agriculture.

The use of plant growth-promoting bacteria (PGPB) is a promising alternative method to improve plant efficiency in the utilization of chemical fertilizers, enabling a reduction of fertilizer application on crops. This study aimed to evaluate the potential of ten Bacillus strains (eight B. subtilis, one B. velezensis and one B. amyloliquefaciens) to promote growth in cotton plants under greenhouse conditions. The experiment was performed in a completely randomized design with 11 treatments and five replicates under greenhouse conditions. The parameters related to plant growth from treatments that received the bacterial isolates were compared to the control. The parameters analyzed were shoot dry matter, root dry matter, total dry matter, plant height, nitrogen content and phosphorus content in soil and in plants. The highest root dry matter was 1.24 g for the isolate 263. The total dry matter was 4.0 g for the isolate 248 and 3.54 g for the isolate 290. The highest chlorophyll content was 28 µg/cm2 for the isolate 290. The higher N content in shoot dry matter was 28 g of N for the isolate 290, 26 g for the isolate 248 and 25 g for the isolate 320. The improved P efficiency use was 32% for the isolate 248, 28% for the isolate 188 and 27% for the isolate 274. These results strongly confirm that B. subtilis isolates 248, 290 and 263 may represent a good alternative as plant growth-promoting endophytes to cotton crops, as they positively affected several parameters evaluated, such as root and shoot dry matter and phosphorus content in the soil. In addition, the parameters evaluated can strongly and positively affect plant yield. However, some isolates of B. subtilis did not promote plant growth and most likely failed as bioinoculants. This result shows the importance of properly identifying the isolate for bioinoculation to achieve success in promoting plant growth.

This study aimed to verify the potential of three Aspergillus and Bacillus species as growth promoters in cotton plants under greenhouse conditions. The experiment was conducted with a completely randomized design with seven treatments (six microorganisms plus one control) and five replicates until the flowering stage at 70 days after emergence. The inoculation of cotton plants with Bacillus velezensis (Bv188) and Bacillus subtilis (Bs248 and Bs290) had a positive effect on total nitrogen extraction (899.31, 962.18, and 755.41 mg N/kg dry matter, respectively) compared to the control (459.31 mg N/kg dry weight), total phosphorus extraction (121.94, 124.31, and 99.27 mg P/kg dry matter, respectively) compared to the control (65.10 mg P/kg dry matter), and total dry matter (41.08, 43.59, and 49.86 g/plant, respectively) compared to the control (26.70 g/plant), as well as biomass carbon (72.26, 35.18, and 14.7 mg/kg soil, respectively). Cotton plants inoculated with Aspergillus brasiliensis (F111), Aspergillus sydowii (F112), and Aspergillus sp. (versicolor section) (F113) had higher total nitrogen extraction (953.33, 812.59, and 891.62 mg N/kg dry matter, respectively) compared to the control (459.31 mg N/kg dry matter), a higher total phosphorus (122.30, 104.86, and 118.45 mg P/kg dry matter, respectively) compared to the control (65.10 mg P/kg dry matter), a higher total dry matter (37.52, 37.41, and 53.02 g/plant) compared to the control (26.70 g/plant), and greater respiratory activity (14.98, 10.43, and 7.11 mg CO2/100 g soil, respectively) compared to the control (3.5 mg CO2/100 g soil). The fungi A. brasiliensis (F111) and A. sydowii (F112) promoted higher phosphorus absorption by cotton plants, which was reflected by the lower amount of nutrients in the soil (7.10 and 16.96 g P/dm3 soil) than in the control (26.91 g P/dm3 soil). The results suggest that B. subtilis 248 promoted an increase in phosphorus extracted from the roots and total and phosphorous compounds from the root dry matter and increased the value of soil respiratory activity, and this bacterium could be used as an inoculant in cotton crops.

There are no studies in literature on the effect of inoculant concentrations on plant growth promotion. Therefore, in the present study, two experiments were carried out, one under pot conditions and the other in the field with cotton crop, in order to verify the effect of Aspergillus and Bacillus concentrations on the biometric and nutritional parameters of plant and soil, in addition to yield. The pot experiment evaluated the effect of different concentrations, ranging from 1 × 104 to 1 × 1010 colony-forming units per milliliter (CFU mL–1) of microorganisms Bacillus velezensis (Bv188), Bacillus subtilis (Bs248), B. subtilis (Bs290), Aspergillus brasiliensis (F111), Aspergillus sydowii (F112), and Aspergillus sp. versicolor section (F113) on parameters plant growth promotion and physicochemical and microbiological of characteristics soil. Results indicated that the different parameters analyzed are influenced by the isolate and microbial concentrations in a different way and allowed the selection of four microorganisms (Bs248, Bv188, F112, and F113) and two concentrations (1 × 104 and 1 × 1010 CFU mL–1), which were evaluated in the field to determine their effect on yield. The results show that, regardless of isolate, inoculant concentrations promoted the same fiber and seed cotton yield. These results suggest that lower inoculant concentrations may be able to increase cotton yield, eliminating the need to use concentrated inoculants with high production cost.

Thraustochytrids are aquatic unicellular protists organisms that represent an important reservoir of a wide range of bioactive compounds, such as essential polyunsaturated fatty acids (PUFAs) such as arachidonic acid (ARA), docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA), which are involved in the regulation of the immune system. In this study, we explore the use of co-cultures of Aurantiochytrium sp. and bacteria as a biotechnological tool capable of stimulating PUFA bioaccumulation. In particular, the co-culture of lactic acid bacteria and the protist Aurantiochytrium sp. T66 induce PUFA bioaccumulation, and the lipid profile was evaluated in cultures at different inoculation times, with two different strains of lactic acid bacteria capable of producing the tryptophan dependent auxins, and one strain of Azospirillum sp., as a reference for auxin production. Our results showed that the Lentilactobacillus kefiri K6.10 strain inoculated at 72 h gives the best PUFA content (30.89 mg g−1 biomass) measured at 144 h of culture, three times higher than the control (8.87 mg g−1 biomass). Co-culture can lead to the generation of complex biomasses with higher added value for developing aquafeed supplements.