Plant Growth Promoting Rhizobacteria (PGPR) is considered as the biological agent for improving plant growth. One Group of PGPR that have an important role in growth promoting of plant is Actinomycetes. The objective of this study was to isolate and screen Actinomycetes isolated from soybean rhizosphere as growth promoter of soybean in vitro. Fifty-three Actinomycetes isolates have successfully been isolated from soybean rhizosphere using two media, mainly Humic acid Vitamin Agar (HVA) and starch casein agar (SCA). Among 53 isolates, 18 (34%) isolates were able to produce IAA in range of 2.08 ppm to 16.70 ppm. Growth promotion test of soybean in vitro using Ragdoll method resulted 7 Actinomycetes isolates that significantly enhanced 3 plant growth parameters, including hypocotyl and radicular length as well as the number of lateral roots. Of those 7 isolates of Actinomycetes, 5 isolates were able to grow on nitrogen-free medium and solubilize phosphate. Those 5 isolates also were found as non-pathogenic, based on the negative reaction in hypersensitivity test. Based on 16S rRNA sequence analysis, 5 selected Actinomycetes isolates were highly homolog with Streptomyces genera in different taxa of species and strains (similarity ≥99%). Our finding reveals a potent application of 5 Actinomycetes isolates as plant growth promoter in soybean agriculture.

Paederia foetida is one of Asia's native plants which is traditionally used for medicinal purposes. The antibacterial and antibiofilm properties of this plant, as well as the identification of its active fractions, have been evaluated in this study. The methanolic extract of dried P. foetida leaves showed antibacterial activity against Escherichia coli and Mycobacterium smegmatis with clear zone diameters of 26 ± 1.4 and 37.6 ± 0.41 mm, respectively, as assessed by the disk diffusion method. Six fractions have been separated using thin-layer chromatography. Of the six fractions tested, two fractions (F5 and F6) possessed antibacterial properties against two tested bacteria. These two fractions have lower minimum inhibitory concentration (MIC) and minimum bactericidal concentration values than those of the crude extract, ranging from 23.43 to 125 µg/ml. More than 50% of M. smegmatis biofilm and 30% of E. coli biofilm formation have been inhibited by the extract and active fractions of this plant. Moreover, two MIC of the extract and fractions were also able to destroy the established biofilm mass of the tested bacteria. As identified using LC-MS/MS, the F5 and F6 fractions have different major components. Linolenic acid, carotenoid, and icosanamide were detected in the F5 fraction. Furthermore, phaeophytin A was detected in the F6 fraction.

In Indonesia, vibriosis is the main disease in shrimp. This disease is caused by Vibrio sp that may decrease the productivity of shrimp cultivation. Thus, exploration for new bioactive compounds as vibriosis biocontrol agent is necessary. Marine sponge-associated bacteria is one of many sources for bioactive compounds. The aim of this study was to screen marine sponge-associated bacteria producing anti-Vibrio sp's bioactive compounds. Total 12 bacterial isolates (15%) of 80 isolates was isolated from marine sponges Hyrtios sp, Verongula sp. and Smenospongia sp. had anti-Vibrio sp activity in different spectra. The hemolytic assay showed that these 12 bacteria were not pathogen. Interestingly, 3 out of 4 potential isolates with the best anti-Vibrio activity have been confirmed to have genes involved in the synthesis of bioactive compounds, mainly Polyketide Synthase (PKS) and Non-Ribosomal Peptide Synthetase (NRPS) based on the occurrence of Ketosynthase (KS) and Adenilase (A) domain, respectively. Based on 16S rRNA gene, those four isolates were highly homolog to the Bacillus sp in different species and strains. Isolate coded as P2.24 was the only bacterium that had the widest spectrum of anti-Vibrio bioactive compounds against three Vibrio sp used i.e., Vibrio harveyi, V. parahaemolyticus, V. vulnificus. Consistently, an anti-Vibrio sp. activity of the P2.24 was also shown by antagonism assay using culture, supernatant and crude extract of the isolate. Our study indicates this bacterial isolate potentially to be further exploited for controlling vibriosis biologically and important for elucidation of bioactive compounds synthesized by this bacterium.

Abstract. Wahyudi AT, Priyanto JA, Fijrina HN, Mariastuti HD, Nawangsih AA. 2019. Streptomyces spp. from rhizosphere soil of maize with potential as plant growth promoter. Biodiversitas 20: 2547-2553. Actinomycete is one group of rhizobacteria that plays an important role as a plant growth promoter. This study was aimed to evaluate the potential of Actinomycetes isolated from maize rhizosphere in promoting plant growth in vitro including their ability to produce IAA, promote maize sprout growth, solubilize phosphate, and grow in N-free medium. Thirty isolates have been isolated from maize rhizosphere using a spread plate method. All 30 isolates were probably not pathogenic to plants as tested by hypersensitivity reaction test on tobacco leaves. Based on the colorimetric assay, 30 isolates (100%) were able to produce IAA with concentrations ranging from 1.05 to 26.89 ppm. The highest concentration of IAA (26.89 ppm) produced by ARJ 21 and the lowest IAA concentration (1.05 ppm) produced by ARJ 12. By using the Ragdoll method, it showed that 9 isolates (30%) were able to promote maize sprout growth significantly on five growth parameters including primary root length, stem length, number of lateral roots, wet weight and dry weight. Twenty-one isolates (70%) were capable of solubilizing phosphate in Pikovskaya medium containing tricalcium phosphate. Also, 30 isolates (100%) were able to grow on N-free medium, suggesting their ability to fix nitrogen. Based on 16S-rRNA, five potential isolates with plant growth-promoting properties were highly similar to Streptomyces spp. Based on their potential characters, these Actinomycetes isolates have the potential to be further developed as a biofertilizer agent for sustainable maize farming.

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