The reproduction process of Gram-positive protocells

Abstract

Bacterial protoplasts are believed to reproduce in a haphazard manner. Their unregulated method of reproduction is considered the simplest of all known forms of cell replication. In the present study, we attempted to understand the evolutionary significance and physiochemical mechanisms behind this process. Here we transformed a Gram-positive bacterium into sack of cytoplasm, incapable of regulating either its morphology or reproductive processes. As such primitive (proto)cells devoid of molecular biological processes could have been native to early Earth, we grew these cells under environmental conditions of early Earth. We then monitored these cells at regular intervals to understand if they can grow and reproduce under these conditions. In our incubations, cells exhibited a multi-stage reproductive cycle resulting in viable daughter cells. What was previously thought to be a chaotic reproductive process, could in fact be well explained from a physicochemical perspective. Both morphology and reproductive process of these cells were determined by chemical and self-assembling properties of their cell constituents rather than the information encoded in their genome. Despite its haphazard appearance, we propose that the reproductive process of bacterial protoplasts is better optimized for environmental conditions of early Earth and could be reminiscent of protocell reproductive processes.Abstract Figure

On the nature of the earliest known lifeforms

“…In this study, we have used an alternative approach to understand early life. We transformed a Gram-positive bacterium (Exiguobacterium Strain-Molly) into its primitive lipid vesicle-like state (EM-P) (27,28). Cells in this state can be described as a simple sack of cytoplasm devoid of all mechanisms to regulate their morphology and reproduction (27).…”

“…We transformed a Gram-positive bacterium (Exiguobacterium Strain-Molly) into its primitive lipid vesicle-like state (EM-P) (27,28). Cells in this state can be described as a simple sack of cytoplasm devoid of all mechanisms to regulate their morphology and reproduction (27). Although it has not been empirically demonstrated, some studies have suggested that cells in this lipid vesiclelike state likely resemble primitive protocells, and their morphology and reproduction are determined by environmental conditions (27)(28)(29).…”

“…Cells in this state can be described as a simple sack of cytoplasm devoid of all mechanisms to regulate their morphology and reproduction (27). Although it has not been empirically demonstrated, some studies have suggested that cells in this lipid vesiclelike state likely resemble primitive protocells, and their morphology and reproduction are determined by environmental conditions (27)(28)(29). Hence, we subsequently studied the life cycle of these cells in their native environment (conditions prevalent on early Earth).…”

“…Given that EM-P's life cycle and the biophysical basis of such a reproduction process is extensively discussed in the previous manuscript (27), the primary focus of this manuscript will be restricted to the morphological comparison of EM-P cells and Archaean Eon microfossils. Below, we present the morphological comparison between EM-P cells and Archaean Eon microfossils.…”

On the annotation of Paleo- and Mesoproterozoic microfossils as fungi

“…One key factor that has fostered the attribution of Paleo-and Mesoproterozoic microfossils from Ongeluk formation ( ˜ 2.4 Ga) 17 , Gunflint iron formations ( ˜ 2Ga) 23 , Grassy Bay formation ( ˜ 1Ga) 18 , and Lakhanda formation ( ˜ 1Ga) 19 , is their similarity in size and basic morphology to extant fungi. However, we have previously shown that bacteria could transform into their protoplast state under some environmental conditions [24][25][26] , and cell wall could have evolved no earlier than ~2 Ga (this manuscript is under preparation). Based on these results, we argue that morphology is not a reliable indicator in the identification of fungal microfossils.…”