Vicky Toussaint

Proteome Analyses of Soil Bacteria Grown in the Presence of Potato Suberin, a Recalcitrant Biopolymer

Suberin is a complex lipidic plant polymer found in various tissues including the potato periderm. The biological degradation of suberin is attributed to fungi. Soil samples from a potato field were used to inoculate a culture medium containing suberin as the carbon source, and a metaproteomic approach was used to identify bacteria that developed in the presence of suberin over a 60-d incubation period. The normalized spectral counts of predicted extracellular proteins produced by the soil bacterial community markedly decreased from day 5 to day 20 and then slowly increased, revealing a succession of bacteria. The population of fast-growing pseudomonads declined and was replaced by species with the ability to develop in the presence of suberin. The recalcitrance of suberin was demonstrated by the emergence of auxotrophic bacteria such as Oscillatoria on the last days of the assay. Nevertheless, two putative lipases from Rhodanobacter thiooxydans (I4WGM2) and Myxococcus xanthus (Q1CWS1) were detected in the culture supernatants, suggesting that at least some bacterial species degrade suberin. When grown in suberin-containing medium, R. thiooxydans strain LCS2 and M. xanthus strain DK 1622 both produced three lipases, including I4WGM2 and Q1CWS1. These strains also produced other proteins linked to lipid metabolism, including fatty acid and lipid transporters and β-oxidation enzymes, suggesting that they participate in the degradation of suberin. However, only the R. thiooxydans strain appeared to retrieve sufficient carbon and energy from this recalcitrant polymer in order to maintain its population over an extended period of time.

Relationships between Xanthomonas campestris pv. vitians population sizes, stomatal density and lettuce resistance to bacterial leaf spot

Abstract The resistance of 10 lettuce cultivars to bacterial leaf spot caused by Xanthomonas campestris pv. vitians (Xcv) was evaluated to establish the relationship between stomatal density, variations in pathogen population size, and the presence of epiphytic Bacillus sp. On the basis of average disease severity index ranked on a scale from 0 to 6, the cultivars were divided into three groups: tolerant, with 2.09; intermediate, with 3.59; and susceptible, with 4.92. The initial inoculum population of the pathogen was slightly increased, by less than 1 logCFU g−1 after 14 d, on only the tolerant cultivars ‘Batavia Reine des Glaces’ and ‘Little Gem’. In contrast to Xcv, the initial inoculum population of Bacillus sp. decreased on all the cultivars, by 1 to more than 2 logCFU g−1, without any significant relationship with the resistance groups. The tolerant cultivars exhibited averages of 40 and 57 stomata mm−2 on the adaxial and abaxial sides of the leaves, respectively; those averages were significantly lower than those of the susceptible cultivars, with 67 and 111 stomata mm−2, respectively. However, the stomatal area of the cultivars varied from 110 to 263 µm2/stomata and 126 to 232 µm2/stomata on the adaxial and abaxial sides of the leaves, respectively. Therefore, no relationship could be established between stomatal area and lettuce cultivar susceptibility. The density of stomata seems to be a good criterion for predicting the degree of tolerance of cultivars, especially when the adaxial side of the leaves is considered.

'SJM15' Apple Rootstock

ABSTRACT The ‘SJM15’ Apple Rootstock is s a new dwarfing apple rootstock developed at the Agriculture and Agri-Food Canada (AAFC) Research Station, St-Jean-sur-Richelieu, Quebec. It produces dwarf trees equal to or slightly smaller than ‘Ottawa 3’ (O.3) and ‘Malling 9’ (M.9). It was released because of its superior hardiness, ease of propagation, and better efficiency compare to ‘O.3’.