Aeromonas Surface Glucan Attached through the O-Antigen Ligase Represents a New Way to Obtain UDP-Glucose

We previously reported that A. hydrophila GalU mutants were still able to produce UDP-glucose introduced as a glucose residue in their lipopolysaccharide core. In this study, we found the unique origin of this UDP-glucose from a branched α-glucan surface polysaccharide. This glucan, surface attached through the O-antigen ligase (WaaL), is common to the mesophilic Aeromonas strains tested. The Aeromonas glucan is produced by the action of the glycogen synthase (GlgA) and the UDP-Glc pyrophosphorylase (GlgC), the latter wrongly indicated as an ADP-Glc pyrophosphorylase in the Aeromonas genomes available. The Aeromonas glycogen synthase is able to react with UDP or ADP-glucose, which is not the case of E. coli glycogen synthase only reacting with ADP-glucose. The Aeromonas surface glucan has a role enhancing biofilm formation. Finally, for the first time to our knowledge, a clear preference on behalf of bacterial survival and pathogenesis is observed when choosing to produce one or other surface saccharide molecules to produce (lipopolysaccharide core or glucan)

Effects of fluctuating moisture and temperature regimes on the persistence of quiescent conidia of Isaria fumosorosea

Conidia of Isaria fumosorosea were submitted to three regimes of temperature and moisture to simulate microclimatic conditions which prevail in temperate (43% RH and 28 degrees C to 98% RH and 15 degrees C), subtropical (75% RH and 35 degrees C to 98% RH and 25 degrees C), and arid areas (13% RH and 40 degrees C to 33% RH and 15 degrees C) with daily fluctuating cycles. Germination, conidial viability, and virulence to Spodoptera frugiperda larvae were less affected after 20 days exposure under temperate cycling conditions than under arid and subtropical conditions. Exposure of conidia for 20 days to constant nocturnal simulated conditions of any tested regime weakly affected conidial persistence, whereas diurnal conditions exerted the most detrimental effects of high temperatures. However, when tested at both 45 degrees C and 50 degrees C at 33% RH for 160 h, the persistence of I. furnosorosea conidia was relatively higher than expected. These results emphasize that climatic conditions prevailing in environments and ecological fitness of fungal isolates have to be taken into account for assessing microbial control strategies

Effects of wetting on the persistence of quiescent conidia of Isaria fumosorosea

Quiescent conidia of Isaria fumosorosea were submitted to various wetting-drying cycles under different regimes of temperature and air humidity. Germination and viability of conidia collected on cultures freshly host-passed (P2) were not affected at 25 degrees C during five cycles at increasing wet phase duration (2-12 h per daily cycle) under any moisture conditions (13-86% RH). Infectivity levels remained stable, but mortality was slightly postponed. In vitro-cultured inocula (P5) were significantly affected after only one cycle at higher air humidity (75 and 86% RH) and temperature (35 and 40 degrees C). The persistence of I. fumosorosea conidia suspended in water soluble extracts of leaf surfaces (corn and cabbage) confirmed the better persistence of P2 conidia and the relatively higher detrimental effect of lower air humidity conditions when combined with moderate temperatures. Quiescent conidia deposited in situ on potted plants of cabbage showed a higher persistence on wet foliage and on foliage submitted to wetting-drying cycles, than on dry foliage. These results underline that constraints prevailing in targeted environments and ecological fitness of fungal isolates have to be taken into account for assessing microbial control strategies

New proposal for a multi-objective technique using Tribes and tabu search

International audienceno abstrac

A study of the hybridization to improve the efficiency of an adaptive particle swarm optimizer

International audienceno abstrac

A new proposal for a multi-objective technique using Tribes and simulated annealing

International audienceno abstrac