Biology subjects

Fu, M. S.

Publications and source records attributed to Fu, M. S..

3 recordsLinked to original sources

bioRxiv2018

The capsule of Cryptococcus neoformans modulates phagosomal pH through its acid-base properties

Phagosomal acidification is a critical cellular mechanism for the inhibition and killing of ingested microbes by phagocytic cells. The acidic environment activates microbicidal proteins and creates an unfavorable environment for the growth of many microbes. Consequently, numerous pathogenic microbes have developed strategies for countering phagosomal acidification through various mechanisms that include interference with phagosome maturation. The human pathogenic fungus Cryptococcus neoformans resides in acidic phagosome after macrophage ingestion that actually provides a favorable environment for replication since the fungus replicates faster at acidic pH. We hypothesized that the glucuronic acid residues in the capsular polysaccharide had the capacity to affect phagosome acidity through their acid-base properties. A ratiometric fluorescence comparison of imaged phagosomes containing C. neoformans to those containing beads showed that the latter were significantly more acidic. Similarly, phagosomes containing non-encapsulated C. neoformans cells were more acidic than those containing encapsulated cells. Acid-base titrations of isolated C. neoformans polysaccharide revealed that it behaves as a weak acid with maximal buffering capacity around pH 4-5. We interpret these results as indicating that the glucuronic acid residues in the C. neoformans capsular polysaccharide can buffer phagosomal acidification. Interference with phagosomal acidification represents a new function for the cryptococcal capsule in virulence and suggests the importance of considering the acid-base properties of microbial capsules in the host-microbe interaction for other microbes with charged residues in their capsules.\n\nImportanceCryptococcus neoformans is the causative agent of cryptococcosis, a devastating fungal disease that affects thousands of individuals worldwide. This fungus has the capacity to survive inside phagocytic cells, which contributes to persistence of infection and dissemination. One of the major mechanisms of host phagocytes is to acidify the phagosomal compartment after ingestion of microbes. This study shows that the capsule of C. neoformans can interfere with full phagosomal acidification by serving as a buffer.

microbiology↗

bioRxiv2018

Dragotcytosis: Elucidation of the Mechanism for Cryptococcus neoformans Macrophage-to-Macrophage Transfer

Cryptococcus neoformans is a pathogenic yeast capable of a unique and intriguing form of cell-to-cell transfer between macrophage cells. The mechanism for cell-to-cell transfer is not understood. Here we imaged macrophages with CellTracker Green CMFDA-labeled cytosol to ascertain whether cytosol was shared between donor and acceptor macrophages. Analysis of several transfer events detected no transfer of cytosol from donor to acceptor macrophages. However, blocking Fc and complement receptors resulted in a major diminution of cell-to-cell transfer events. The timing cell-to-cell transfer (11.17 min) closely approximated the sum of phagocytosis (4.18 min) and exocytosis (6.71 min) times. We propose that macrophage cell-to-cell transfer represents a non-lytic exocytosis event followed by phagocytosis into a macrophage that is in close proximity and name this process Dragotcytosis (Dragot is a Greek surname meaning Sentinel) as it represents sharing of a microbe between two sentinel cells of the innate immune system.

microbiology↗

bioRxiv2017

Divalent metal cations potentiate the predatory capacity of amoeba for Cryptococcus neoformans

Among the best studied interaction between soil phagocytic predators and a human pathogenic fungus is that of Acanthamoeba castellanii and Cryptococcus neoformans. The experimental conditions used in amoeba-fungal confrontation assays can have major effects on whether the fungus or the protozoan is ascendant in the interaction. In the presence of Mg2+ and Ca2+ in PBS, C. neoformans was consistently killed when incubated with A. castellanii. A. castellanii survived better in the presence of Mg2+ and Ca2+, even when incubated with C. neoformans. In the absence of Mg2+ and Ca2+, C. neoformans survived when incubated with A. castellanii, and the percentage of dead amoeba was higher than when incubated without yeast cells. These results show that the presence of Mg2+ and Ca2+ can make a decisive contribution toward tilting the outcome of the interaction in favor of amoeba. Of the two metals Mg2+ had a stronger effect than Ca2+. Cations enhanced A. castellanii activity against C. neoformans through enhanced phagocytosis, which is the major mechanism for amoeba to kill fungal cells. We found no evidence that amoeba uses extracellular killing mechanisms in their interactions with C. neoformans. In summary, the presence of Mg2+ and Ca2+ enhanced cell adhesion on surface and motility of amoeba, thus increasing the chance for contact of C. neoformans and the frequency of phagocytosis. Our findings imply that divalent cation concentration in soils could be an important variable for whether amoeba can control C. neoformans in the environment.\n\nImportanceGrazing of soil organisms by phagocytic predators such as amoeba is thought to select for traits that allow some of them to acquire the capacity for virulence in animals. Consequently, knowledge about the interactions between amoeba and soil microbes, such as pathogenic fungi, is important for understanding how virulence can emerge. We show that the interaction between amoeba and the pathogenic fungus C. neoformans is influenced by the presence of magnesium and calcium in the assay, which potentiate amoeba. The results may also have practical applications since enriching soils with divalent cations may reduce C. neoformans numbers in contaminated soils.

microbiology↗