Effects of acc deaminase-producing plant growth-promoting bacteria from myrothamnus flabellifolius (welw.) On wheat growth under drought stress
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Date
2025
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University of Namibia
Abstract
The rise in global population compounded by global climatic patterns continue to
drastically aggravate arid regions with susceptibility to various abiotic stress
conditions. This situation impacts agricultural sustainability, further compromising
food security. However, plants growing in hostile environments have become well
adapted to their habitats, employing strategies to mitigate the impacts of drought
stress by mutualistic association and interaction with 1-aminocyclopropane-1-
carboxylate (ACC) deaminase plant growth-promoting bacteria (PGPB). This study
was therefore, designed to isolate, characterize and identify bio-prospective ACC
deaminase PGPB associated with Myrothamnus flabellifolius (Welw.), a Namibian
desert-adapted plant. A total of 52 isolates of bacteria were isolated from M.
flabellifolius of which 33 underwent molecular identification using 16S rRNA, acdS,
and nifH gene sequence alignment, and 29 were further characterized for plant
growth promoting (PGP) traits. Ten different genera namely Bacillus (12),
Pseudomonas (6), Cupriavidus (5), Enterobacteriacea (2), Kosakonia (3),
Agrobacterium (1), Klebsiella (1), Staphylococcus (1), Enterobacter (1) and
Cellulosimicrobium (1) were identified, with Bacillus as the most abundant genera
(36.4%). Isolates were selected for their ability to produce ACC deaminase and other
PGP traits, and drought tolerance evaluated using four different polyethylene glycol
(PEG) 6000 concentrations. From the 29 isolates that were characterized and deemed
positive for ACC deaminase, the highest ACC deaminase activity value was
exhibited by Bacillus licheniformis (R13) 0.0013 ± 0.01 mM of α-ketobutyrate. The
highest drought tolerance at 30% PEG 6000 was exhibited by Staphylococcus
hominis (LB3) and Bacillus licheniformis (R13), 0.52 ± 0.37 and 0.35 ± 0.18
respectively. Three ACC deaminase-producing strains, coupled with PGP traits and
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drought stress tolerance, Kosakonia sp., Cupriavidus metallidurans, and
Pseudomonas sp. were selected and evaluated for their response to improve wheat
(Triticum aestivum L.) germination and early growth under drought stress. Proline
levels and enzymatic activity were evaluated on seedlings. Seed treatment with
Kosakonia sp. strain displayed significant growth enhancement (P<0.005) in various
growth parameters evaluated under drought stress conditions in contrast to
Pseudomonas sp. C. metallidurans and the control. Proline levels significantly
differed across categories of bacterial isolate treatments (P<0.01), with Kosakonia
sp. treated seeds exhibiting the highest level of proline per fresh weight (29.5
µmoles/g) and Pseudomonas sp. exhibiting the lowest (6.5 µmoles/g). There was no
significant difference in levels of proline produced during various PEG-induced
drought conditions. Enzymatic activity (α-amylase) was significantly influenced by
bacterial treatments with the control significantly reducing the enzymatic activity in
contrast to other treatments. This study showed that reducing water potential
decreases germination percentage (GP) and various growth parameters. Additionally,
bacterial isolates such as Kosakonia sp. have the potential to promote growth and
serve as potential microbes in the development of effective bioinoculants for
sustainable agricultural crops in arid regions. The study is the first report on
prospective microbes from M. flabellifolius inhabiting Namibia
Description
A thesis submitted in partial fulfilment of the requirements for the Degree of Master of Science in Microbiology
Keywords
Myrothamnus flabellifolius, Plant growth promoting bacteria, Drought, Desert, Namibia, University of Namibia