Plant growth-promoting potential of bacterial endophytes isolated from Lessertia frutescens

• Lessertia frutescens is a medicinal plant that harbours many bacteria endophytes. • Endophytes of Lessertia frutescens have potential plant growth promoting attributes. • Two native Bacillus species are ideal candidates for bio-fertilization. Many endophytic bacteria have plant growth promoting attributes that could improve agricultural yield as well as resistance to various types of stress and disease. Detection of such attributes usually involves in vitro screening and the subsequent testing of the isolates on the plants for specific or combined effects on germination, seedling growth and yield. Despite many studies in this field, there is a knowledge gap on the influence of endophytes on early growth of certain economically important plants such as medicinal plants. In the present study, we evaluated the in vitro capabilities of bacterial endophytes isolated from Lessertia frutescens (L.) Goldblatt & J.C.Manning (syn. Sutherlandia frutescens (L.) W.T.Aiton) for plant growth promotion and their effect on initial seedling growth. Using a culture-dependent approach, plant samples of Lessertia frutes cens were screened for bacterial endophytes. The isolated bacterial endophytes were subsequently evaluated for their plant growth-promoting attributes along with their ability to produce hydrolytic enzymes. Molecular identification of selected endophytic bacteria based on the 16S rRNA genes of strains that tested negative in the hemolysis test was conducted. The two most promising isolates were evaluated for their ability to promote Lessertia frutescens seedling growth in a two-month pot trial study. The obtained results revealed that many of the bacterial endophytes had potential to promote plant growth. Specifically, 86 % of the endophytes possessed nitrogen-fixing, phosphate solubilizing, and IAA-producing abilities, while approximately 71 % were able to exhibit siderophore-producing capabilities. The endophytes exhibited significant production of essential hydrolytic enzymes, including amylase (86 %), gelatinase (86 %), protease (29 %), lipase (43 %), and D-nase (57 %). The two best isolates were identified as relatives of Bacillus spp. (Bacillus licheniformis BaDB06 and Bacillus velezensis strain SM-95). Their plant growth-promoting properties such as their ability to enhance plant height and their ability to be used as bio-agent were further confirmed in the pot trial study as they enhanced the growth of Lessertia frutescens seedlings compared to the control. This study provides insights into the functional roles of endophytic bacteria of Lessertia frutescens in seedling growth and their potential plant growth enhancement, highlighting their potential for sustainable agriculture and ecosystem management.