Biology subjects

Rahaman, A.

Publications and source records attributed to Rahaman, A..

3 recordsLinked to original sources

bioRxiv2025

Observing Grazing Behavior Transitions in Cafeteria roenbergensis with Video-Rate Two-Photon Microscopy

Grazing behavior of free-living aquatic heterotrophic nanoflagellates (HNFs) on bacteria plays a central role in shaping microbial community structure and nutrient cycling. However, direct observation of these interactions has been limited by the rapid motility of flagellates and the transient nature of predator-prey encounters. To address this gap, this study presents a novel application of video-rate two-photon fluorescence microscopy for high resolution, real-time imaging of fast-moving microorganisms. HNF Cafeteria roenbergensis is used as a model system to investigate dynamic grazing interactions between fluorescently stained bacteria and the flagellates, where the flagellates are detected via their intrinsic cellular autofluorescence. This two-photon microscope combined with real-time imaging capability enables continuous capture of contact, capture, ingestion, and digestion steps during grazing. Quantitative analysis across varying prey concentration reveals phase-specific durations and saturation behavior in grazing activities. Furthermore, transitions in grazing dynamics across two continuous periods of flagellates in starved and fed conditions are observed in live time series videos. This technique provides a powerful new tool to study rapid microbial interactions in situ and can be broadly applicable to diverse microbe-microbe systems. With the integration of targeted fluorescent molecular probes, this technique holds significant potential for uncovering mechanical and biochemical interactions underlying microbial feeding and communication. SignificanceThis study significantly advances microbial ecology by applying video-rate two-photon fluorescence microscopy to directly visualize and quantify the rapid grazing behavior of flagellates on bacteria. By enabling real-time observation of contact, ingestion, and digestion during the grazing events, the technique overcomes limitations of traditional imaging. It captures behavioral transitions tied to physiological states, offering quantitative insight into microbial predator-prey dynamics. This method establishes a broadly applicable platform for studying fast, transient microbial interactions. Although current limitations include the lack of 3D tracking, emerging optical technologies promise enhanced capabilities, paving the way for deeper understanding of microbial processes in aquatic ecosystems.

biophysics↗

bioRxiv2025

Self-assembly is important for the target membrane recruitment of a nuclear dynamin-related protein

Dynamin superfamily proteins are large GTPases that perform their cellular functions by self-assembling on their target membranes. Dynamin-related protein 6 (Drp6) associates with the nuclear membrane and performs nuclear remodeling. However, the mechanism of its recruitment to the target membrane is not known. Here, we discover that self-assembly of Drp6 is essential for its nuclear membrane recruitment. We identified four residues, 411-GKFR-414 to be essential for its self-assembly. We also demonstrated that the mutant Drp6 (Drp6GKFR-AAAA) failed to recruit to the nuclear membrane. This loss of nuclear membrane recruitment is not due to the lack of membrane binding capability, since the mutated protein was able to bind membrane prepared in vitro. Together, our results suggest that in addition to membrane binding, self-assembly of a nuclear dynamin-related protein is also important for the target membrane recruitment.

cell biology↗

bioRxiv2020

Cardiolipin targets a dynamin related protein to the nuclear membrane

Dynamins are large cytoplasmic GTPases that are targeted to specific cellular membranes which they remodel via membrane fusion or fission. Although the mechanism of target membrane selection by dynamins has been studied, the molecular basis of conferring specificity to bind specific lipids on the target membranes is not known in any of the family members. Here, we report a mechanism of nuclear membrane recruitment of Drp6 that is involved in nuclear remodeling in Tetrahymena thermophila. Recruitment of Drp6 depends on a domain that binds to cardiolipin-rich bilayers. Consistent with this, the nuclear localization of wildtype Drp6 was inhibited by depleting cardiolipin in the cell. Cardiolipin binding was blocked with a single amino acid substitution (I553M) in the membrane-binding domain of Drp6. Importantly, the I553M substitution was sufficient to block nuclear localization without affecting other properties of Drp6. Consistent with this result, co-expression of wildtype Drp6 was sufficient to rescue the localization defect of I553M variant in Tetrahymena. Inhibition of cardiolipin synthesis or perturbation in Drp6 recruitment to nuclear membrane caused defects in the formation of new macronuclei post-conjugation. Taken together, our results elucidate a molecular basis of target membrane selection by a nuclear dynamin, and establish the importance of a defined membrane-binding domain and its target lipid in facilitating nuclear expansion.

cell biology↗