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Production of indole acetic acid by endophytic Bacillus strains

Nabrdalik Małgorzata

Ecological Chemistry and Engineering. A

2018

Vol. 25, nr 1

93--105

The objectives of this study were to isolate and characterize endophytic bacteria from sugar beet roots focusing on their ability to produce indole acetic acid (IAA). In order to isolate endophytic bacteria the sugar beet roots were used. To determine the amounts of IAA produced by endophytic Bacillus strains (B. amyloliquefaciens, B. megaterium and B. subtilis), a colorimetric technique was applied with Salkowski reagent. The isolates were grown in Laurin Broth medium supplemented with L-tryptophan over the concentration range of 100–10000 g/cm3 and incubated at 30 oC for 7 days. The highest concentration of IAA was recorded after 4 days of culturing in the supernatant obtained from the media containing 10000 g/cm3 of tryptophan. For the strain B. subtilis and B. megaterium the concentration of IAA marked in the post –culturing liquid amounted about 82.00 g/cm3, and for the B. amyloliquefaciens strain it amounted over 121.28 g/cm3. The strains Bacillus under study produced IAA in a different amount in the presence of L-tryptophan and in its absence.

Celem pracy było wyizolowanie i scharakteryzowanie bakterii endofitycznych korzeni buraka cukrowego pod kątem ich zdolności do produkcji kwasu indolilooctowego (IAA). Materiał doświadczalny do izolacji bakterii endofitycznych stanowiły korzenie burak cukrowego. Ilość wytworzonego IAA przez endofityczne szczepy Bacillus (B. amyloliquefaciens, B. megaterium, B. subtilis) oznaczono metodą kolorymetryczną z odczynnikiem Salkowskiego. Szczepy hodowano w pożywce LB (Laurin Broth) suplementowanej L-tryptofanem w stężeniach 100–10000 g/cm3 i inkubowano w 30 oC przez 7 dni. Najwyższe stężenie IAA odnotowano po 4 dniach w hodowlach zawierających 10000 g/cm3 L-tryptofanu. Dla szczepu B. subtilis i B. megaterium stężenie IAA wynosiło około 82,00 g/cm3, a dla szczepu B. amyloliquefaciens 127,28 g/cm3. Badane szczepy Bacillus spp. wytwarzały IAA na różnym poziomie zarówno w obecności L-tryptofanu jak i przy jego braku.

Response of birch and alder root endophytes as well as rhizosphere and bulk soil microorganisms to heavy metal pollution

Złoch M., Kowalkowski T., Szymańska S., Hrynkiewicz K.

Polish Journal of Ecology

2014

Vol. 62, nr 1

37--53

Research on soil microorganisms associated with plant roots (endophytes) and their outside habitats (rhizosphere, soil) under exposure to high concentrations of heavy metals in the environment may contribute to an increased knowledge about the effects of unfavorable pollutants in the natural ecosystem and improve the efficiency of remediation processes of degraded soils. The main goal of our study was to evaluate properties of microbial populations inhabiting different but spatially closed habitats: interior of the tree roots – endophytes (Betula pendula L. and Alnus glutinosa L.), rhizosphere and soil not influenced by plant roots at two heavy metal polluted areas in southern Poland where the content of cadmium, lead and zinc ranged 9.2–14.9, 26.2–75.1 and 1080–1559 mg∙kg-1 of dried soil, respectively. In our experiment, we analyzed their density as well as determined the total metabolic activity and ability for utilization of different carbon sources. The density of endophytes (5.76–7.16 log10 c.f.u. × g dw-1) was higher than the density of bacteria inhabiting outside habitats – the rhizosphere and soil (5.43–5.91 and 5.08–5.57 log10 c.f.u. × g dw-1, respectively) and was not affected by heavy metal content. However, the total metabolic activity of endophytic populations was strongly influenced by the physicochemical properties of the soil and was significantly lower at more contaminated site. In general, the metabolic activity of endophytes was ~15 times lower than the activity of rhizobacteria and at the same level or lower than the activity of soil microorganisms. Discriminant analysis revealed a higher utilization of α-Cyclodextrin and D-Xylose by microorganisms isolated from more polluted test site. The use of an artificial neural network (ANN) followed by principal component analysis (PCA) allowed the distinguishing of preferences in the utilization of carbon sources by microorganisms due to tree species but not the zone of isolation – endophytes, rhizosphere, soil. Our study revealed no significant impact of the metal concentrations present in the soil on the density of microorganisms (bacteria and fungi) inhabiting three analyzed zones (interior of the roots, rhziosphere, soil); however, their total metabolic activity was decreased in more contaminated site. Since the density of endophytes was higher compared to the number of bacteria present in the outside habitats (rhizosphere and soil), and their total metabolic activity was in general lower, we suggest a high specialization of microorganisms associated with the cellular spaces of plant roots compared to other microbial populations.