Tannins reportedly alter absorption and utilization of protein and minerals. The present study investigated the effect of tannins extracted from 'Mississippi Silver' cowpeas and black tea when incorporated into nutritionally balanced diets. Condensed tannins were incorporated into the diet of weanling male Sprague-Dawley rats at 0.0, 0.0057, 0.0171 and 0.057 g/100 g diet for 28 d. Ingestion of tannin from cowpeas or tea did not change significantly growth rate, protein efficiency ratio, apparent protein digestibility, nitrogen excretion, relative liver weight, or nitrogen concentration of liver. During d 11-18, apparent calcium absorption was lower in rats fed the medium and high levels of cowpea tannin and in those fed all levels of tea tannin compared with the control group. By wk 4, no differences were observed in apparent calcium absorption among treatment groups. Apparent magnesium absorption was not affected by dietary treatment, nor was femur content of calcium or magnesium. We conclude that at the levels of condensed tannins fed, a short-term reduction of apparent calcium absorption occurred; however, by wk 4 calcium absorption was comparable to that of the control group. The acute change that occurred in apparent calcium absorption did not influence bone calcium content.

Tannins were analyzed on three cultivars of cowpeas at three maturity stages. Cultivars differed in testa darkening which increased during maturation. Darker testa had greater tannin concentrations. Testa tannins increased up to 7-fold during maturation and up to 96% of the tannins were found in the testa. The sum of tannins in individually tested cotyledon and testa was up to 10.7 times greater than that found from analysis of whole cowpea after grinding to 20-mesh. Heating in water reduced whole cowpea tannins 38-76%; cotyledon 53-59%, and testa 66-75%.

Microbial colonization of plant roots is a highly complex process that requires the coordination and regulation of many gene networks, yet the identities and functions of many of these gene products have yet to be discovered. Pantoea sp. YR343, a gamma-proteobacterium isolated from the rhizosphere of Populus deltoides, forms robust biofilms along the root surfaces of Populus and possesses plant growth-promoting characteristics. In this work, we identified three diguanylate cyclases in the plant-associated microbe Pantoea sp. YR343 that are expressed in the presence of plant roots. One of these diguanylate cyclases, DGC2884, localizes to discrete sites in the cells and its overexpression results in reduced motility and increased EPS production and biofilm formation. We performed a genetic screen by expressing this diguanylate cyclase from an inducible promoter in order to identify candidate gene products that may be involved in root colonization by Pantoea sp. YR343. Further, we demonstrate the importance of other domains in DGC2884 to its activity, which in combination with the genes identified by transposon mutagenesis, may yield insights into the mechanisms of plant association as well as the activity and regulation of homologous enzymes in medically and agriculturally relevant microbes.

The relative toxicity of 46 para-position alkyl- and halogen-substituted pyridines, cyanobenzenes, nitrobenzenes, phenols, benzyl alcohols, and benzaldehydes was determined by measuring the population growth impairment (log BR) of the ciliate Tetrahymena pyriformis. The 1-octanol/water partition coefficient (log KOW)-dependent quantitative structure-activity relationship (QSAR) for the pyridines, cyanobenzenes, and nitrobenzenes is log BR = 0.8222 (log KOW) - 1.7889; n = 19, r2 = 0.937, and s = 0.155. A similar QSAR for the phenols, benzyl alcohols, and benzaldehydes is log BR = 0.6360 (log KOW) - 1.2012; n = 27, r2 = 0.726, and s = 0.284 (where n = the number of data points; r2 = the coefficient of determination; and s = root mean square.) The predictability of the latter QSAR is improved by the addition of the orthogonal field electronic parameter F. The resulting QSAR is log BR = 0.7891 (log KOW) + 0.6793 (F) - 1.7457; n = 27, r2= 0.925, and s = 0.163.

Microbial colonization of plant roots is a highly complex process that requires the coordination and regulation of many gene networks, yet the functions of many of these gene products remain poorly understood.  Pantoea sp. YR343, a gamma-proteobacterium isolated from the rhizosphere of Populus deltoides , forms robust biofilms along the root surfaces of Populus and possesses plant growth-promoting characteristics. The mechanisms governing biofilm formation along plant roots by bacteria, including Pantoea sp. YR343, are not fully understood and many genes involved in this process have yet to be discovered.  In this work, we identified three diguanylate cyclases in the plant-associated microbe Pantoea sp. YR343 that are expressed in the presence of plant roots, One of these diguanylate cyclases, DGC2884 localizes to discrete sites in the cells and its overexpression results in reduced motility and increased EPS production and biofilm formation.  We then performed a genetic screen by expressing this diguanylate cyclase from an inducible promoter in order to identify candidate downstream effectors of c-di-GMP signaling which may be involved in root colonization by Pantoea sp. YR343.  Further, we demonstrate the importance of other domains in DGC2884 to its activity, which in combination with the genes identified by transposon mutagenesis, may yield insights into activity and regulation of homologous enzymes in medically and agriculturally relevant microbes.