Biology subjects

Suma, H. R.

Publications and source records attributed to Suma, H. R..

3 recordsLinked to original sources

bioRxiv2026

The enemy of my enemy: A bacterial antagonist rescues Chlamydomonas by inactivating a toxin from a rival

Microbial interactions are shaped by multiple community members, yet the underlying mechanisms remain poorly understood. Here, we investigated a tripartite interaction between the microalga Chlamydomonas reinhardtii and two Pseudomonas bacteria that coexist in the same soil habitat. In pairwise cultures, all three interactions are amensalistic (-like): Pseudomonas protegens Pf-5 antagonizes both C. reinhardtii and Pseudomonas fluorescens HKI0770 without benefit, while P. fluorescens inhibits C. reinhardtii without profiting from the alga. However, in a tripartite culture, P. fluorescens protects C. reinhardtii from P. protegens and promotes algal recovery. This protection is not stopped when the used carbon source, acetate, is supplemented. The P. fluorescens rescue effect is associated with reduced levels of the polyyne toxin protegencin produced by P. protegens. Protegencin levels, detected by Raman microspectroscopy, are decreased by application of spent medium or protein extracts from P. fluorescens, while heat- and protease-treatment abolish this activity. A heat-sensitive, proteinaceous factor, likely an enzyme(s), appears to contribute to protegencin inactivation. Our results show that P. fluorescens rescues C. reinhardtii by inactivating protegencin, despite being inhibited by P. protegens. These findings demonstrate the importance of investigating higher-order effects, since additional community members can transform pairwise antagonistic interactions into conditional protection through toxin inactivation.

microbiology↗

bioRxiv2024

Pleiotropic regulation of bacterial toxin production and Allee effect govern microbial predator-prey interactions

Bacteria are social organisms, which are constantly exposed to predation by nematodes or amoebae. To counteract these predation pressures, bacteria have evolved a variety of potent antipredator strategies. Bacteria of the genus Pseudomonas, for instance, evade amoebal predation by the secretion of amoebicidal natural products. The soil bacterium Pseudomonas fluorescens HKI0770 produces pyreudione alkaloids that can kill amoebae. Even though the mode of action of the pyreudiones has been elucidated, the spatiotemporal dynamics underlying this predator-prey interaction remain unknown. Using a combination of microscopic and analytical techniques, we elucidated the intricate relationship of this predator-prey association. We used the chromatic bacteria toolbox for intraspecific differentiation of the amoebicide-producing wildtype and the non-producing mutant within microcosms. These allow for variations in nutrient availability and the emergence of predation-evasion strategies of interacting microorganisms. Imaging of the co-cultures revealed that the amoebae initially ingest both the non-producer as well as the toxin-producer cells. The outcomes of predator-prey interactions are governed by the population size and fitness of the interacting partners. We identified that changes in the cell density coupled with alterations in nutrient availability led to a strong Allee effect resulting in the diminished production of pyreudione A. The loss of defence capabilities renders P. fluorescens HKI0770 palatable to amoebae. Such a multifaceted regulation provides the basis for a model by which predator-prey populations are being regulated in specific niches. Our results demonstrate how the spatiotemporal regulation of bacterial toxin production alters the feeding behaviour of amoebae.

microbiology↗

bioRxiv2019

Naturally occurring fluorescence protects the eutardigrade Paramacrobiotus sp. from ultraviolet radiation

Naturally occurring fluorescence has been observed in multiple species ranging from bacteria to birds. In macroscopic animals such as birds and fishes, fluorescence provides a visual communication signal. However, the functional significance of this phenomenon is not known in most cases. Though photoprotection is attributed to fluorescence under ultraviolet (UV) light in some organisms, it lacks direct experimental evidence. Here, we have identified a new species of eutardigrade belonging to the genus Paramacrobiotus, which exhibits fluorescence under UV light. Using a natural variant of the same species that lacks fluorescence, we show that the fluorescence confers tolerance to lethal UV radiation. Remarkably, we could transfer this property to UV-sensitive Hypsibius exemplaris, another eutardigrade, and also to C. elegans, a nematode. Using high performance liquid chromatography (HPLC) we isolated the fluorescent compound from Paramacrobiotus sp. This compound has excitation maxima ({lambda}ex) at 370 nm and emission maxima ({lambda}em) at 420-430 nm. We propose that Paramacrobiotus sp. uses a fluorescent shield that absorbs harmful UV radiation, and emits harmless blue light, thereby protecting itself from the lethal effects of UV radiation. Summary statementTardigrades are well known for their tolerance to extreme environmental conditions. In this study, we have identified a new tardigrade species that employs a fluorescent shield to protect itself from the germicidal ultra violet radiation.

ecology↗