Indian Institute of Science (IISc) and the University of Agricultural Sciences (UAS), Bengaluru, have found that Salmonella, an infectious bacteria, is seen to contaminate pre-harvest and the bacteria is seen to enter the plant even from infected soil.
The study was conducted by a four-member team of scientists from IISc, led by Prof Utpal Nath of the Department of Microbiology and Cell Biology, IISc, and Prof Nataraja Karaba from UAS.
“We always had a thought that post-harvest contamination may not be the only source for outbreaks of salmonella contamination in tomatoes. That led us to investigate whether salmonella can infect plants,” Prof Dipshikha Chakravortty, ASTRA Chair Professorship, DAE SRC Fellow, Humboldt Fellow, Department of Microbiology and Cell Biology, IISc, told F&B News.
“UAS is our long-term collaborator and this research spanned for over a period of four-and-a-half years. Moreover, even if there was no specific grant for this research, we received a general funding under the DBT-IISc partnership programme. No specific funding for this study, said Prof Chakravortty, who is also associate faculty, biosystems science and engineering, IISc.
“Now we would like to share our ideas with farmers and suggest a few solutions to this problem to them,” she said.
The research efforts, which were published in the BMC Plant Biology journal, stated, “Pre-harvest contamination of fruits and vegetables by Salmonella in fields is one of the causes of food-borne outbreaks. Natural openings like stomata, hydathodes and fruit cracks are known to serve as entry points.”
“While there are reports indicating that Salmonella colonise and enter root through lateral root emerging area, further investigations regarding how the accessibility of Salmonella to lateral root is different from phyto-pathogenic bacteria, the efficacy of lateral root to facilitate entry have remained unexplored,” they added.
“In this study we attempted to investigate the lateral root mediated entry of Salmonella, and to bridge this gap in knowledge,” the research efforts said.
“To understand the ecological significance, we induced lateral root production by increasing soil salinity which made the plants susceptible to Salmonella invasion and the plants showed higher Salmonella burden in the aerial organs,” said Kapudeep Karmakar, PhD student, Department of Microbiology and Cell Biology, IISc, and first author of the paper published in BMC Plant Biology.
The researchers also noted how varied types of bacteria, including Salmonella, colonised the roots of the tomato plant. Salmonella, being unable to degrade plant cell wall material, relies heavily on natural openings. Therefore, its invasion is highly dependent on the number of lateral roots, which provides an entry point, because of the epidermis remodelling.
“When a number of lateral roots were enhanced by increasing the soil salinity, plants became susceptible to Salmonella invasion in roots and its transmission to aerial organs,” said the article.
The entry point of Salmonella in plants is well-studied. They enter the aerial organs through the openings such as stomata, hydathodes and fruit cracks. Unlike aerial organs, below ground organs are in direct contact with the contaminated soil.
“Salmonella can become systemic after its entry into the plant and can colonise the aerial organs. As an extension of the study, we have examined soil stress factor (salinity) in transmission of Salmonella from soil to the aerial organs,” explained the researchers in the article.
