Revisiting the Mechanisms Involved in Calcium Chloride Induced Bacterial Transformation

Fatty acid and their amide derivatives are natural self-defense agents in plants. They have been observed to be broadly bioactive against a variety of disease agents. The mechanism of action understood so far being their targeting the protein synthesis and causing leakage of the intracellular components. Owing to their broad bioactivity, the fatty acids and their amides as therapeutics can cover a wide range of indications such as cancer, bacterial infections, parasitic infection, inflammations, diabetes and obesity to name a few. The microorganisms residing inside the healthy plant tissues are a unique niche for exploration of novel bioactive compounds. The recent identification of fatty acid amide derivatives as well as prior reports from endophytes have drawn fresh attention to this unique source for their isolation. Hence, they represent an exciting opportunity for the development of new therapeutic agents against existing disease causative agents. In this paper, we will discuss the production of fatty acids and amide derivatives by plants and their associated endophytes. Their reported bioactivities establishing their potential benefit as possible therapeutic agents will also be examined.

Pakistan is blessed with plants of Asteraceae family with known medicinal background used for centuries by Hakims (traditional physicians). Keeping in mind the background of their anti-larval potential, a total of 21 endophytic actinomycetes were isolated from four Asteraceae plants and screened against the first and fourth instar stages of Culex quinquefasciatus Say mosquito larvae. Of the 21 isolates, 6 of them gave strong larvicidal activity (80–100% mortality) in the screening results and 4 isolates gave a potent larvicidal activity (100% mortality) at the fourth instar stage. These isolates belonged to different species within the actinomycetes group, namely Streptomyces albovinaceus and Streptomyces badius. This communication reports the larvicidal potential of endophytic actinomycetes residing within the native Asteraceae plants in Pakistan. The study suggests further exploration through large-scale productions leading to the identification of the larvicidal compounds.

In many areas of developing countries, agriculture soil is irrigated with water from drains contaminated with industrial wastewater that contains many toxic substances including arsenic. Such sites could be explored for arsenic-resistant plant growth-promoting microbes. Ten arsenic-resistant bacteria were isolated from such a site and were characterized. Their ability to resist and reduce/oxidize arsenic was determined. The bacteria were also analyzed for plant growth-promoting abilities such as auxin and hydrogen cyanide production, phosphate solubilization, and nitrogen fixation. The effect of these bacteria on plant growth was determined using Vigna radiata both in presence and absence of arsenic. Bacterial isolates S254 and S255 showed maximum resistance against arsenic; up to 225 mM of As(V) and 25 mM of As(III). The phylogenetic analysis revealed that strain S254 belonged to the species Pseudoxanthomonas mexicana and strain S255 belonged to the species Stenotrophomonas maltophilia. Both P. mexicana S254 and S. maltophilia S255 showed positive results for hydrogen cyanide production, auxin production, and nitrogen fixation. P. mexicana S254 produced auxin at a concentration of 14.15 µg mL⁻¹ and S. maltophilia S255 produced auxin as high as 68.75 µg mL⁻¹. Both the bacteria-enhanced the growth of V. radiata and a statistically significant increase in shoot and root lengths was observed both in the presence and absence of arsenic. The application of such bacteria could be helpful for the growth of plants in arsenic-contaminated lands.