Identification and Characterization of Nucleotide Sequence Differences in Three Virulence-Associated Genes of Listeria monocytogenes Strains Representing Clinically Important Serotypes

Listeria monocytogenes is a Gram-positive, facultative intracellular bacterium that causes invasive, often fatal, disease in susceptible hosts. As a foodborne pathogen, the bacterium has emerged as a significant public health problem and has caused several epidemics in the United States and Europe. Three serotypes (1/2a, 1/2b, 4b) of L. monocytogenes are responsible for nearly 95% of all reported cases of human listeriosis. L. monocytogenes serotype 4b has caused all well-characterized foodborne epidemic outbreaks in North America and Europe between 1981 and 1993. However, most of the genetic studies to characterize virulence factors of L. monocytogenes have been done by using serotypes 1/2a and 1/2c. In this investigation, we examined three virulence-associated genes (hly encoding listeriolysin, plcA encoding phosphotidylinositol-specific phospholipase C, and inlA encoding internalin) of two serotype 4b and two serotype 1/2b strains. We chose these virulence-associated genes on the basis of published sequence differences among strains from Listeria subgroups containing serotypes 1/2a and 1/2c versus 4b, respectively. They correspond to sequence homologies that include very highly conserved (hlyA), highly conserved (plcA) and mostly conserved (inlA). We found by using nucleotide sequence analysis of the hly, plcA, and inlA genes, the two L. monocytogenes strains (including a strain associated with a foodborne disease outbreak in California in 1985) in this study, two serotype 1/2b strains from a study that we recently reported, and other similar published data for serotypes 1/2a, 1/2c, and 4b, had a high degree of sequence conservation at the gene and protein levels for all three genes. However, the sequences for the hly gene of L. monocytogenes strains of serotypes 1/2b and 4b were more closely related to each other and showed significant divergence from serotypes 1/2a and 1/2c. A unique nonsynonymous mutation was found in the hly gene of L. monocytogenes isolates that were associated with the 1985 California outbreak and were the epidemic phage type. When 158 L. monocytogenes isolates from the collection at the Centers for Disease Control and Prevention were screened, the mutation was found only in one other strain that had been isolated in California 3 years before the epidemic. Although the California epidemic clone was lactose negative, other L. monocytogenes serotype 4b isolates that were lactose negative did not possess the unique mutation observed in that epidemic clone. Received: 18 June 1997 / Accepted: 4 December 1997     

A Study on the nature of genetic divergence in rice from assam and North East Himalayas

Summary A representative group of 190 rice types collected from North-East India along with four standard varieties, three of which were indicas and one japonica, was studied to understand the nature of genetic divergence. Preliminary grouping was done by canonical analysis and the resultant 42 groups were further classified using the D² statistic.The final grouping resulted in nine divergent clusters. The three indica standards were found in three different clusters indicating the wide available variability among them. The japonica standard formed a separate group by itself. A majority of the North-East Indian types formed clusters with indicas, whereas some were intermediate and still others were closer to japonica or indica, thus indicating a series of intergrades bridging indica and japonica.Height followed by leaf area was found to be important for primary and 100-grain weight, followed by amylose content for secondary differentiation. It appears that natural selection as well as human selection might have operated for characters differentiating rice types in Assam and North Eastern Himalayas. Geographical distance was not found to be related to genetic divergence. The study suggests that O. sativa contains innumerable but divergent forms, and its classification into definite varietal groups on an arbitrary basis such as isolation barrier, sexual affinity or geographic distribution would be far from reality.     

Strategies and models for agricultural sustainability in developing Asian countries

The green revolution of the 1960s and 1970s which resulted in dramatic yield increases in the developing Asian countries is now showing signs of fatigue in productivity gains. Intensive agriculture practiced without adherence to the scientific principles and ecological aspects has led to loss of soil health, and depletion of freshwater resources and agrobiodiversity. With progressive diversion of arable land for non-agricultural purposes, the challenge of feeding the growing population without, at the same time, annexing more forestland and depleting the rest of life is indeed daunting. Further, even with food availability through production/procurement, millions of marginal farming, fishing and landless rural families have very low or no access to food due to lack of income-generating livelihoods. Approximately 200 million rural women, children and men in India alone fall in this category. Under these circumstances, the evergreen revolution (pro-nature, pro-poor, pro-women and pro-employment/livelihood oriented ecoagriculture) under varied terms are proposed for achieving productivity in perpetuity. In the proposed 'biovillage paradigm', eco-friendly agriculture is promoted along with on- and non-farm eco-enterprises based on sustainable management of natural resources. Concurrently, the modern ICT-based village knowledge centres provide time- and locale-specific, demand-driven information needed for evergreen revolution and ecotechnologies. With a system of 'farm and marine production by masses', the twin goals of ecoagriculture and eco-livelihoods are addressed. The principles, strategies and models of these are briefly discussed in this paper.     

Anaerobic denitrification in fungi from the coastal marine sediments off Goa, India

Denitrification is a microbial process during which nitrate or nitrite is reduced under anaerobic condition to gaseous nitrogen. The Arabian Sea contains one of the major pelagic denitrification zones and in addition to this, denitrification also takes places along the continental shelf. Prokaryotic microorganisms were considered to be the only players in this process. However recent studies have shown that higher microeukaryotes such as fungi can also adapt to anaerobic mode of respiration and reduce nitrate to harmful green house gases such as NO and N₂O. In this study we examined the distribution and biomass of fungi in the sediments of the seasonal anoxic region off Goa from two stations. The sampling was carried out in five different periods from October 2005, when dissolved oxygen levels were near zero in bottom waters to March 2006. We isolated mycelial fungi, thraustochytrids and yeasts. Species of Aspergillus and thraustochytrids were dominant. Fungi were isolated under aerobic, as well as anaerobic conditions from different seasons. Four isolates were examined for their denitrification activity. Two cultures obtained from the anoxic sediments showed better growth under anaerobic condition than the other two cultures that were isolated from oxic sediments. Our preliminary results suggest that several species of fungi can grow under oxygen deficient conditions and participate in denitrification processes.