Membrane fatty acid composition and fluidity are involved in the resistance to freezing of Lactobacillus buchneri R1102 and Bifidobacterium longum R0175
Authors: Louesdon, Severine; Charlot-Rouge, Severine; Tourdot-Marechal, Raphaelle; Bouix, Marielle; Beal, Catherine
Determinations of membrane fatty acid composition and fluidity were used together with acidification activity and viability measurements to characterize the physiological state after freezing of Lactobacillus buchneriR1102 and Bifidobacterium longumR0175 cells harvested in the exponential and stationary growth phases. For both strains, lower membrane fluidity was achieved in cells harvested in the stationary growth phase. This change was linked to a lower unsaturated-to-saturated fatty acid ratio for both strains and a higher cyclic-to-saturated fatty acid ratio for L.buchneriR1102 alone. These membrane properties were linked to survival and to maintenance of acidification activity of the cells after freezing, which differed according to the strain and the growth phase. Survival of B.longumR0175 was increased by 10% in cells with low membrane fluidity and high relative saturated fatty acid contents, without any change in acidification activity. Acidification activity was more degraded (70min) in L.buchneriR1102 cells displaying low membrane fluidity and high saturated and cyclic fatty acid levels. Finally, this study showed that membrane modifications induced by the growth phase differed among bacterial strains in terms of composition. By lowering membrane fluidity, these modifications could be beneficial for survival of B.longumR0175 during the freezing process but detrimental for maintenance of acidification activity of L.buchneriR1102.
Morphotype Transition and Sexual Reproduction Are Genetically Associated in a Ubiquitous Environmental Pathogen
Authors: Wang, Linqi; Tian, Xiuyun; Gyawali, Rachana; Upadhyay, Srijana; Foyle, Dylan; Wang, Gang; Cai, James J.; Lin, Xiaorong
Sexual reproduction in an environmental pathogen helps maximize its lineage fitness to changing environment and the host. For the fungal pathogen Cryptococcus neoformans, sexual reproduction is proposed to have yielded hyper virulent and drug resistant variants. The life cycle of this pathogen commences with mating, followed by the yeast-hypha transition and hyphal growth, and it concludes with fruiting body differentiation and sporulation. How these sequential differentiation events are orchestrated to ensure developmental continuality is enigmatic. Here we revealed the genetic network of the yeast-to-hypha transition in Cryptococcus by analyzing transcriptomes of populations with a homogeneous morphotype generated by an engineered strain. Among this network, we found that a Pumilio-family protein Pum1 and the matricellular signal Cfl1 represent two major parallel circuits directing the yeast-hypha transition. Interestingly, only Pum1 coordinates the sequential morphogenesis events during a-a bisexual and a unisexual reproduction. Pum1 initiates the yeast-to-hypha transition, partially through a novel filament-specific secretory protein Fas1; Pum1 is also required to sustain hyphal growth after the morphological switch. Furthermore, Pum1 directs subsequent differentiation of aerial hyphae into fruiting bodies in both laboratory and clinical isolates. Pum1 exerts its control on sexual reproduction partly through regulating the temporal expression of Dmc1, the meiosis-specific recombinase. Therefore, Pum1 serves a pivotal role in bridging post-mating morphological differentiation events with sexual reproduction in Cryptococcus. Our findings in Cryptococcus illustrate how an environmental pathogen can ensure the completion of its life cycle to safeguard its long-term lineage success.