Methane in pristine and impaired mangrove soils and its possible effect on establishment of mangrove seedlings

Pristine and impaired mangrove soils (from road construction, aquaculture, and sewage) in Baja California Sur, Mexico were investigated for methane dynamics, related soil properties, and their impact on initial establishment of black mangrove propagules. All soils (Salic Fluvisols and Histosols) had neutral to alkaline pH, were saline, and had variable organic carbon content, and redox potentials. Most pristine mangrove soils showed low methane concentration, low methane production rates, and no methane emission. Impaired mangrove soil (from aquaculture) and mangrove soil affected by sewage water showed high methane concentration, high methane production rates, and high methane emission, thus acting as a methane source. Elevated methane concentrations, similar to levels detected in the impaired mangrove soil, reduce the growth of seedlings under closed chamber conditions. Addition of sulfate to the soil reversed the trend. These results indicate that impaired mangrove soils in dry climatic regions produce and emit methane and that elevated methane concentration in the vicinity of propagules may affect establishment of mangrove seedlings in impaired mangrove soils. This paper is in memory of the late mangrove researcher Dr. Gina Holguin of Mexico.     

Crop loss of pepper plants artificially infected with Xanthomonas campestris pv. vesicatoria in relation to symptom expression

Crop losses in peppers artificially infected with Xanthomonas campestris pv. vesicatoria (XCV) were determined during 3 years of field experiments in three areas of Israel. Direct losses of 23–44% in fruit yield were recorded when severe leaf infection occurred or was induced at an early stage of plant growth. Yield losses and disease index were markedly lower in plants inoculated at later stages and near maturation. Indirect losses in severely infected fields were mainly due to shedding of leaves and exposure of fruits to sun. In this case, up to 95% of the fruits lost their commercial value. In artificially infected symptomless plants with massive endogenous populations of XCV in the leaves, a loss of 24% in yield was measured, compared with plants free from an endogenous pathogen population.     

Restoration of giant cardon cacti in barren desert soil amended with common compost and inoculated with Azospirillum brasilense

Barren desert soil that otherwise could not support perennial plant growth was amended with six levels of common agricultural compost. Seedlings of the giant cardon cactus, one of the primary plant species responsible for soil stabilization in the southern Sonoran Desert, were inoculated with the plant-growth-promoting bacterium Azospirillum brasilense Cd, planted, and grown for 18 months under nursery conditions typical for slow-growth cacti. Control plants were grown without compost amendment, without inoculation (negative control), or in fertile, rare “resource island” soil preferred by cardon seedlings (positive control). During the prolonged growth period, the decisive factor in seedling growth in barren soil was the addition of small amounts of common compost; 6 to 25% of the growth substrate volume gave the best growth response and, to a lesser extent, so did inoculation with A. brasilense Cd. Although the bacteria significantly affects plant growth when amended with “resource island” soil and added to barren soil, its effect on plant growth was far smaller than when compost alone was added. Compost added to barren soil significantly increased the dry weight parameters of the plant to almost similar levels obtained by the “resource island” soil; however, the compost amendment supports a more voluminous and greener plant with elevated pigment levels. This study shows that barren soil supplemented with compost can replace the rare “resource island” soil for cardon nurseries destined to abate soil erosion in the desert.     

The role of sediment microorganisms in the productivity, conservation, and rehabilitation of mangrove ecosystems: an overview

Mangrove communities are recognized as highly productive ecosystems that provide large quantities of organic matter to adjacent coastal waters in the form of detritus and live animals (fish, shellfish). The detritus serves as a nutrient source and is the base of an extensive food web in which organisms of commercial importance take part. In addition, mangrove ecosystems serve as shelter, feeding, and breeding zones for crustaceans, mollusks, fish of commercial importance, and resident and migratory birds. Although mangroves in the United States are protected, the systematic destruction of these ecosystems elsewhere is increasing. Deforestation of mangrove communities is thought to be one of the major reasons for the decrease in the coastal fisheries of many tropical and subtropical countries. There is evidence to propose a close microbe-nutrient-plant relationship that functions as a mechanism to recycle and conserve nutrients in the mangrove ecosystem. The highly productive and diverse microbial community living in tropical and subtropical mangrove ecosystems continuously transforms nutrients from dead mangrove vegetation into sources of nitrogen, phosphorus, and other nutrients that can be used by the plants. In turn, plant-root exudates serve as a food source for the microorganisms living in the ecosystem with other plant material serving similarly for larger organisms like crabs. This overview summarizes the current state of knowledge of microbial transformations of nutrients in mangrove ecosystems and illustrates the important contributions these microorganisms make to the productivity of the ecosystems. To conserve the mangrove ecosystems, which are essential for the sustainable maintenance of coastal fisheries, maintenance and restoration of the microbial communities should be undertaken. Inoculation of mangrove seedlings with plant-growth-promoting bacteria may help revegetate degraded areas and create reconstructed mangrove ecosystems.     

Reproducible induction of cavity spot in carrots and physiological and microbial changes occurring during cavity formation

Inoculation of carrots with 40 types of bacteria, both aerobic and anaerobic, including clostridia isolated from cavity spots, failed to induce cavity spot in carrots. A combined stress of minimum 6 h flooding and temperatures higher than 28°C clearly induced cavity formation. Sugars, amino acids, lipids and minerals leaked from the carrots after flooding and heating the roots. A longer growth period following stress markedly increased cavity spots. Soil types (sandy loam and loess) and several carrot cultivars tested had no marked effect on spot formation. Cavities were formed in stressed carrots grown in sterilized soil containing only one type of bacterium, a Gram-negative short rod. Scanning electron micrographs revealed that after carrots were subjected to combined stress, microscopic cavities nearly free of bacteria were formed under the epidermis. Proliferation of bacteria was concommitant with the appearance of visible cavities. Cell-free extracts of infected carrots showed higher protease and pectinase-specific activities, as well as significantly higher peroxidase and polyphenoloxidase activities and total phenol content as compared to healthy carrots.     

Increase in auxiliary photoprotective photosynthetic pigments in wheat seedlings induced by Azospirillum brasilense

Inoculation of wheat seedlings with the plant growth-promoting bacterium Azospirillum brasilense Cd was immobilized in alginate microbeads and, without applying any stress, significantly increased the quantity of several photosynthetic pigments, such as chlorophyll a, chlorophyll b, and the auxiliary photoprotective pigments violaxanthin, zeaxanthin, antheroxanthin, lutein, neoxanthin, and β-carotene. This resulted in greener plants with no apparent visible stress. After monitoring the quantity of photosynthetic pigments for 4 weeks, we observed that inoculated plants had higher quantities of pigments in shoot and stem. The greatest difference in the quantity of all pigments between inoculated and noninoculated plants occurred in the first week of growth. Regardless of treatment, the quantity of pigments in stems was three to four times less than the quantity of these pigments in shoots. Application of Azospirillum, either as liquid inoculant or as alginate microbeads, did not alter the positive effect of the bacteria on pigment production or the positive response of the plants towards A. brasilense Cd inoculation.     

The Rag GTPases bind raptor and mediate amino acid signaling to mTORC1

The multiprotein mTORC1 protein kinase complex is the central component of a pathway that promotes growth in response to insulin, energy levels, and amino acids and is deregulated in common cancers. We find that the Rag proteins--a family of four related small guanosine triphosphatases (GTPases)--interact with mTORC1 in an amino acid-sensitive manner and are necessary for the activation of the mTORC1 pathway by amino acids. A Rag mutant that is constitutively bound to guanosine triphosphate interacted strongly with mTORC1, and its expression within cells made the mTORC1 pathway resistant to amino acid deprivation. Conversely, expression of a guanosine diphosphate-bound Rag mutant prevented stimulation of mTORC1 by amino acids. The Rag proteins do not directly stimulate the kinase activity of mTORC1, but, like amino acids, promote the intracellular localization of mTOR to a compartment that also contains its activator Rheb.     

A common variant in the FTO gene is associated with body mass index and predisposes to childhood and adult obesity

Obesity is a serious international health problem that increases the risk of several common diseases. The genetic factors predisposing to obesity are poorly understood. A genome-wide search for type 2 diabetes-susceptibility genes identified a common variant in the FTO (fat mass and obesity associated) gene that predisposes to diabetes through an effect on body mass index (BMI). An additive association of the variant with BMI was replicated in 13 cohorts with 38,759 participants. The 16% of adults who are homozygous for the risk allele weighed about 3 kilograms more and had 1.67-fold increased odds of obesity when compared with those not inheriting a risk allele. This association was observed from age 7 years upward and reflects a specific increase in fat mass.