Cell walls are crucial for the integrity and function of all land plants and are of central importance in human health, livestock production, and as a source of renewable bioenergy. Many enzymes that mediate the biosynthesis of cell wall polysaccharides are encoded by members of the large () gene superfamily. Here, we analyzed 29 sequenced genomes and 17 transcriptomes to revise the phylogeny of the gene superfamily in angiosperms. Our results identify ancestral gene clusters that predate the monocot-eudicot divergence and reveal several novel evolutionary observations, including the expansion of the Poaceae-specific cellulose synthase-like family to the graminids and restiids and the characterization of a previously unreported eudicot lineage, , that forms a reciprocally monophyletic eudicot-monocot grouping with the clade. The lineage is widely distributed in eudicots, and the clade, which was thought previously to be restricted to the Poales, is widely distributed in monocots. Our analyses show that some members of the lineage, but not the newly identified genes, are capable of directing (1,3;1,4)-β-glucan biosynthesis, which, contrary to current dogma, is not restricted to Poaceae.
Swarming motility, a flagellum-dependent behavior that allows bacteria to move over solid surfaces, has been implicated in biofilm formation and bacterial virulence. In this study, light and electron microscopic analyses and genetic and functional investigations have shown that at least 50% of Aeromonas isolates from the species most commonly associated with diarrheal illness produce lateral flagella which mediate swarming motility. Aeromonas lateral flagella were optimally produced when bacteria were grown on solid medium for Ϸ8 h. Transmission and thin-section electron microscopy confirmed that these flagella do not possess a sheath structure. Southern analysis of Aeromonas reference strains and strains of mesophilic species (n ؍ 84, varied sources and geographic regions) with a probe designed to detect lateral flagellin genes (lafA1 and lafA2) showed there was no marked species association of laf distribution. Approximately 50% of these strains hybridized strongly with the probe, in good agreement with the expression studies. We established a reproducible swarming assay (0.5% Eiken agar in Difco broth, 30°C) for Aeromonas spp. The laf-positive strains exhibited vigorous swarming motility, whereas laf-negative strains grew but showed no movement from the inoculation site. Light and scanning electron microscopic investigations revealed that lateral flagella formed bacteriumbacterium linkages on the agar surface. Strains of an Aeromonas caviae isolate in which lateral flagellum expression was abrogated by specific mutations in flagellar genes did not swarm, proving conclusively that lateral flagella are required for the surface movement. Whether lateral flagella and swarming motility contribute to Aeromonas intestinal colonization and virulence remains to be determined.
An undescribed bacterium capable of clearing tannic acid‐protein complexes has been isolated from ruminal contents of feral goats browsing tannin‐rich Acacia species. The bacterium is a Gram‐positive facultative anaerobe, characterized as a Streptococcus, but DNA‐DNA hybridization and 16S rDNA sequencing show that it is distinct from the common ruminal species Strep. bovis. We propose the name Streptococcus caprinus for this species. The type strain is Strep. caprinus 2.3, Australian Collection of Microorganisms (ACM) 3969. The bacterium grows in media containing at least 2.5% w/v tannic acid or condensed tannin and produces zones of clearing around colonies on nutrient agar plates with added tannic acid. Streptococcus caprinus is not a major inhabitant of domestic livestock, but is found in feral goats browsing tannin‐rich Acacia species, at a population of up to 2 times 106 cfu ml‐1 of rumen fluid.
Streptococcus gallolyticus (S. caprinus) was resistant in vitro to at least 7 % (w/v) tannic acid and 4 % (w/v) acacia condensed tannin, levels 10-fold greater than those tolerated by S. bovis. Growth of S. gallolyticus in liquid medium was characterized by a lag period which increased, and a growth rate which decreased, with increasing tannin concentration. S. gallolyticus was also more tolerant to the presence of simple phenolic acid monomers than was S. bovis, but the lag period was still concentration dependent. Gallate decarboxylase activity in S. gallolyticus was elevated in the presence of tannic acid or gallic acid but not with other phenolic acids. Scanning electron microscopic analysis showed that both the size and shape of S. gallolyticus and S. bovis changed in response to tannin but only S. gallolyticus was surrounded by an extracellular polysaccharide matrix which accumulated in a tannin-concentration-dependent fashion. Washing of the cells to remove extracellular polysaccharide increased the lag period of S. gallolyticus in the presence of 1 % (w/v) tannic acid from 4 h to 6 h. In contrast, increasing extracellular polysaccharide synthesis in S. bovis did not increase its tolerance to tannic acid. These data demonstrate that S. gallolyticus has developed a number of mechanisms to reduce the potential effect of tannins on cell growth, and that these mechanisms provide the organism with a selective advantage over S. bovis when grown in the presence of tannins.
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