Bradyrhizobium japonicum FN1 produces an inhibitory substance that affects competition for nodule occupancy

Bacteriocins are narrow spectrum antibiotics of bacterial origin that can affect competition in resource-limited environments such as the rhizosphere. Therefore, bacteriocins may be good candidates for manipulation in order to generate more competitive inocula for soybean. In this study,<i> B. japonicum</i> FN1 along with other Bradyrhizobia in our culture collection were screened for bacteriocin-like activity. A total of five distinct inhibitory activities could be observed. FN1 genes putatively involved in bacteriocin production were computationally identified. These genes were mutagenized and the subsequent strains were screened for loss of inhibitory activity. Mutant strain BRJ-48, with an insert in<i> bjfn1_01204</i>, displayed a loss of the ability to inhibit an indicator strain. This loss could be complemented by the introduction of a plasmid expressing <i>bjfn1_01204 </i>in trans. The strain carrying the mutation did not affect competition in broth cultures, but was shown to be less competitive for nodule occupancy. Annotation suggests that <i>bjfn1_01204</i> encodes a carboxymuconolactone decarboxylase, however the direct contribution of how this enzyme contributes to inhibiting the tester strain remains unknown.

Recovery of a Bacteriocin-Like Inhibitory Substance from Lactobacillus bulgaricus FTDC 1211 Using Polyethylene-Glycol Impregnated Amberlite XAD-4 Resins System

Lactobacillus bulgaricus is a LAB strain which is capable of producing bacteriocin substances to inhibit Staphylococcus aureus. The aim of this study was to purify a bacteriocin-like inhibitory substance (BLIS) produced by L. bulgaricus FTDC 1211 using an aqueous impregnated resins system consisting of polyethylene-glycol (PEG) impregnated on Amberlite XAD4. Important parameters influencing on purification of BLIS, such as the molecular weight and concentration of PEG, the concentration and pH of sodium citrate and the concentration of sodium chloride, were optimized using a response surface methodology. Under optimum conditions of 11% (w/w) of PEG 4000 impregnated Amberlite XAD4 resins and 2% (w/w) of sodium citrate at pH 6, the maximum purification factor (3.26) and recovery yield (82.69% ± 0.06) were obtained. These results demonstrate that AIRS could be used as an alternate purification system in the primary recovery step.

Assessment of allelopathic potential of Dalbergia cochinchinensis Pierre and its growth inhibitory substance

In forestry systems, many types of forest trees possess allelopathic properties and release a wide variety of allelochemicals that influence the growth and development of surrounding species. Dalbergia cochinchinensis, a forest tree distributed in Southeast Asia, is reputed to possess several biological properties and contain several secondary compounds. However, there have been no studies on the allelopathy of D. cochinchinensis. Therefore, D. cochinchinensis leaf extracts were examined for allelopathic potential. The present study showed that D. cochinchinensis extracts significantly inhibited the seedling growth of six test plant species: timothy, Italian ryegrass, barnyard grass, cress, alfalfa, and lettuce. Concentrations of the D. cochinchinensis extracts negatively correlated with the shoot length (r = −0.50 to −0.89) and root length (r = −0.65 to −0.89) of all the test plant species. The extracts were then purified using several chromatographic steps and the growth inhibitory substance was isolated. The chemical structure of the substance was identified through spectroscopic analysis as 3,4-dihydroxybenzoic acid (protocatechuic acid). Protocatechuic acid at a concentration higher than 3 mM significantly inhibited the growth of cress seedlings, whereas barnyard grass seedlings were inhibited at concentrations higher than 0.3 mM. As the protocatechuic acid concentration increased, the seedling growth of cress and barnyard grass was significantly reduced. I50 values showed the effectiveness of protocatechuic acid against both test plant species was apparently greater on root growth than shoot growth. Results of this study suggest that protocatechuic acid isolated from D. cochinchinensis might be responsible for its inhibitory effects.