Forty isolates of endophytic bacteria isolated from banana tree roots were assessed as to their capacity to solubilize phosphate in a solid culture medium supplemented with different inorganic and one organic source of phosphorus. The amount of phosphorus (P) in each liquid medium was quantified, and an indirect assessment of acid phosphatase activity was performed. All assays had a fully randomized design, with three repetitions. Approximately 67.5% of the 40 isolates assessed in solid medium solubilized phosphorus from tricalcium phosphate and 7.5% of the isolates solubilized phosphorus from soy lecithin; no isolates exhibited P solubilization capacity in medium supplemented with iron phosphate. Acid phosphatase activity was detected in 65% of the isolates; Aneurinibacillus sp. and Lysinibacillus sp. isolates presented with the best solubilization indexes. All of the assessed isolates exhibited a capacity to reduce the potential of hydrogen in liquid medium supplemented with tricalcium phosphate. Isolate EB. 78 (Bacillus sp.) exhibited P solubilization capacity in solid media when Ca3(PO4)2 and soy lecithin were used as P sources; this isolate significantly reduced the pH of the liquid medium and exhibited acid phosphatase activity. The results of the present study highlight isolates that exhibit variations in their capacity to solubilize P. These isolates should be used in future tests to assess their field performance.

A total of 40 endophytic bacterial isolates obtained from banana tree roots were characterized for their biotechnological potential for promoting banana tree growth. All isolates had at least one positive feature. Twenty isolates were likely diazotrophs and formed pellicles in nitrogen-free culture medium, and 67% of these isolates belonged to the genus Bacillus sp. The isolates EB-04, EB-169, EB-64, and EB-144 had N fixation abilities as measured by the Kjeldahl method and by an acetylene reduction activity assay. Among the 40 isolates, 37.5% were capable of solubilizing inorganic phosphate and the isolates EB-47 and EB-64 showed the highest solubilization capacity. The isolate EB-53 (Lysinibacillus sp.) had a high solubilization index, whereas 73% of the isolates had low solubilization indices. The synthesis of indole-3-acetic acid (IAA) in the presence of L-tryptophan was detected in 40% of the isolates. The isolate EB-40 (Bacillus sp.) produced the highest amount of IAA (47.88 μg/ml) in medium supplemented with L-tryptophan and was able to synthesize IAA in the absence of L-tryptophan. The isolates EB-126 (Bacillus subtilis) and EB-47 (Bacillus sp.) were able to simultaneously fix nitrogen, solubilize phosphate and produce IAA in vitro. The results of this study demonstrated that the isolates analyzed here had diverse abilities and all have the potential to be used as growth-promoting microbial inoculants for banana trees.

The genetic diversity of endophytic bacteria in banana 'Prata Anã' roots was characterized. Two hundred and one endophytic bacteria were isolated, 151 of which were classified as Gram-positive and 50 as Gram-negative. No hypersensitivity response was observed in any of the isolates. The rep-PCR technique generated different molecular profiles for each primer set (REP, ERIC and BOX). Fifty readable loci were obtained and all of the fragments were polymorphic. Amplified ribosomal DNA restriction analysis (ARDRA) of the isolates based on cleavage with four restriction enzymes yielded 45 polymorphic bands and no monomorphic bands. PCR amplified the nifH gene in 24 isolates. 16S rDNA sequencing of the 201 bacterial isolates yielded 102 high-quality sequences. Sequence analyses revealed that the isolates were distributed among ten bacterial genera (Agrobacterium, Aneurinibacillus, Bacillus, Enterobacter, Klebsiella, Lysinibacillus, Micrococcus, Paenibacillus, Rhizobium and Sporolactobacillus) and included 15 species. The greatest number of isolates belonged to the genus Bacillus. The bacteria identified in this study may be involved in promoting growth, phosphate solubilization, biological control and nitrogen fixation in bananas.