The functional characterisation of soybean (Glycine max L.) rhizospheric bacteria indigenous to Ethiopian soils

Abstract

Ethiopia remains a net importer of soybean partly due to low average yields which may be improved by inoculation with rhizobia and/or plant growth promoting rhizobacteria (PGPR). The functional characterisation of 231 rhizobacteria isolated from the rhizosphere of soybean grown in 102 soils collected from different pedo-climatic regions of Ethiopia was carried out. Isolates were initially characterised by Gram staining and then functionally for: indole-3-acetic acid production; phosphate solubilisation; growth on a nitrogen-free medium; and, resistance to the pathogenic fungus Fusarium oxysporum. A subset of 72 of the best performing isolates were tested in vitro for: production of bioprotectants; polysaccharide degradation; and their relative capacity to maintain growth in response to extremes of: temperature; pH; salinity; antibiotics; pesticides; and, heavy metals. Twenty isolates with the best PGPR potential were identified via 16S rRNA gene sequencing. Seventeen isolates were Gram-negative: Pseudomonas (7); Stenotrophomonas (5); Acinetobacter (3); Enterobacter (1); and Achromobacter (1). Gram-positive types were: Bacillus (2); and, Microbacterium (1). Of the six of the most promising PGPR tested on soybean plants, Achromobacter and Acinetobacter significantly enhanced soybean seed germination, seedling growth and plant vigour index compared to noninoculated plants.

Identification of Bacterial Isolates Recovered from the Surface of Cleanroom Operators’ Garments following Wear

“…In contrast, Microbacterium martipicum was uniquely recovered from male workers clothing. Aside from the identification of this species in soil (86), there is little further information about this organism within the literature. However, it should be noted that as with Bacillus, species of Microbacterium have been shown to exhibit very similar 16S rRNA gene sequencing profiles and may be difficult to identify accurately at species level (87).…”