High-tech laboratory methods to explain how endophytic bacteria would live within plant cells

For the first time, international scientists have explained how healthy plants tend to hold bacteria in their cells, opening up a new area of research to enhance potential plant health and propagation efforts—including food crops such as fruit like grapes, as well as grains.

The Indian and Australian researchers used a variety of high-tech laboratory techniques to explain how endophytic bacteria would live within plant cells, resulting in the “baffling” definition of “alien life” in healthy plant cells.

It’s baffling how this bacterial association in cell cultures escaped the attention of plant biologists and microbiologists considering that this is a widespread phenomenon in plant tissue cultures we tested, and the in-vitro cultures have long been used in both basic and applied research.”

Chris Franco, Senior Professor, Flinders University

Dr Pious Thomas, previously from the Indian Institute of Horticultural, and Flinders Emeritus Professor Franco, who collaborated on the study, call them Cytobacts and suggest cytobacteria have been commonly found in micro-propagating stocks in crops such as papaya and banana.

T Pious and CMM Franco’s paper, titled “Intracellular Bacteria in Plants: Elucidation of Abundant and Diverse Cytoplasmic Bacteria in Healthy Plant Cells Using In Vitro Cell and Callus Cultures (2021),” was published in Microorganisms.

Dr Thomas, currently CEO and Director of Thomas Biotech and Cytobacts Centre for Biosciences in Bengaluru, India, who began the work during a research stint at Flinders University ten years ago, has published the findings with senior Flinders University medical biotechnology researcher Emeritus Professor Franco.

I am excited to expand this new field of plant cell biology in my R&D center at Bengaluru with the plan to focus on endophytic microorganisms and allied areas with a primary focus on micropropagation of papaya which is severally hampered due to interference from microbial contaminants. Normally the endophytic bacteria are known to reside between plant cells.”

Dr Pious Thomas, Emeritus Professor Franco, Flinders University

Dr Thomas served as a visiting scientist at Flinders University with Professor Franco 10 years ago.

“Because plant cells are considered to be free of other living organisms it goes against the grain to report bacteria within plant cells. We need new tools to be able to study the role of these intracellular bacteria in healthy plants which are not normally amenable for conventional microbiological methods,” said Thomas.

This new paradigm of cytobacteria in health cells has the potential to open up a whole new area of research, including plant biology, human health and environmental microbiology.”

Chris Franco, Senior Professor, Flinders University

Professor Franco, a veteran biotechnology scientist at Flinders University, retired this year from the College of Medicine and Public Health with over 100 papers to his name in a long research career.

According to him, the landmark research indicates that Cytobacts may have evolved in plant species after losing some of their roles and capacity to synthesize compounds, allowing them to become obligate symbionts of the plant cell.

“Potentially they are involved in some of the integral functions of plants, such as energy metabolism, or as an inducer of defense responses against other microorganisms,” said Franco.

The researchers would like to thank the Indian Council for Agricultural Research (ICAR) and the Department of Biotechnology in New Delhi, Flinders University and the Microscopy and Imaging Facility, as well as cell lines from Flinders, CSIRO Plant Industry, and the University of Melbourne’s School of Botany for their support.