AUTHOR=Kharadi Roshni R. , Sundin George W. 

TITLE=Physiological and Microscopic Characterization of Cyclic-di-GMP-Mediated Autoaggregation in Erwinia amylovora

JOURNAL=Frontiers in Microbiology

VOLUME=10

YEAR=2019

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2019.00468

DOI=10.3389/fmicb.2019.00468

ISSN=1664-302X

ABSTRACT=<p>The second messenger cyclic-di-GMP (c-di-GMP) is a critical regulator of biofilm formation in the plant pathogen <italic>Erwinia amylovora</italic>. Phosphodiesterase (PDE) enzymes are responsible for the degradation of intracellular c-di-GMP. Previously, we found that the deletion of one or more of the three PDE enzyme encoding genes (<italic>pdeA</italic>, <italic>pdeB</italic>, and <italic>pdeC</italic>) in <italic>E. amylovora</italic> Ea1189 led to an increase in biofilm formation. However, in mutants Ea1189Δ<italic>pdeAC</italic> and Ea1189Δ<italic>pdeABC</italic>, biofilm formation was reduced compared to the other single and double deletion mutants. Here, we attribute this to an autoaggregation phenotype observed in these two mutants. Examination of Ea1189Δ<italic>pdeABC</italic> cellular aggregates using scanning electron microscopy indicated that a subset of cells were impaired in cell separation post cell division. Concomitant with this phenotype, Ea1189Δ<italic>pdeABC</italic> also exhibited increased transcription of the cell-division inhibitor gene <italic>sulA</italic> and reduced transcription of <italic>ftsZ</italic>. Ea1189Δ<italic>pdeABC</italic> showed a significant reduction in biofilm formation, and biofilms formed by Ea1189Δ<italic>pdeABC</italic> exhibited a distinctive morphology of sparsely scattered aggregates rather than an evenly distributed biofilm as observed in WT Ea1189. Our results suggest that highly elevated levels of c-di-GMP lead to increased cell–cell interactions that contribute to autoaggregation and impair cell-surface interaction, negatively affecting biofilm formation.</p>