A wide range of microorganisms produce extracellular polymeric substances (EPS), highly hydrated polymers that are mainly composed of polysaccharides, proteins and DNA. EPS are fundamental for microbial life and provide an ideal environment for chemical reactions, nutrient entrapment and protection against environmental stresses such as salinity and drought. Microbial EPS can enhance the aggregation of soil particles and benefit plants by maintaining the moisture of the environment and trapping nutrients. In addition, EPS have unique characteristics, such as biocompatibility, gelling and thickening capabilities, with industrial applications. However, despite decades of research on the industrial potential of EPS, only a few polymers are widely used in different areas, especially in agriculture. This review provides an overview of current knowledge on the ecological functions of microbial extracellular polymeric substances (EPS) and their application in agricultural soils to improve soil particle aggregation, an important factor for soil structure, health and fertility.

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Microbial Extracellular Polymeric Substances: Ecological Function and Impact on Soil Aggregation.

Understanding and exploiting plant beneficial microbes.

Isothermal calorimetry measures the heat flow of biological processes, which is proportional to the rate at which a given chemical or physical process takes place. Modern isothermal microcalorimeters make measurements of less than a microwatt of heat flow possible. As a result, as few as 10 000-100 000 active bacterial cells in culture are sufficient to produce a real-time signal dynamically related to the number of cells present and their activity. Specimens containing bacteria need little preparation, and isothermal microcalorimetry (IMC) is a nondestructive method. After IMC measurements, the undisturbed samples can be evaluated by any other means desired. In this review, we present a basic description of microcalorimetry and examples of microbiological applications of IMC for medical and environmental microbiology. In both fields, IMC has been used to quantify microbial activity over periods of hours or even days. Finally, the recent development of highly parallel instruments (up to 48 channels) and the constantly decreasing costs of equipment have made IMC increasingly attractive for microbiology. Miniaturization of isothermal calorimeters provides an even wider range of possibilities.

Use of isothermal microcalorimetry to monitor microbial activities

Understanding the molecular mechanisms for the enhanced phytoremediation of heavy metals through plant growth promoting rhizobacteria: A review.

Organic and inorganic fertilizers are used primarily to increase nutrient availability to plants. Monitoring balanced versus unbalanced fertilization effects on soil microbes could improve our understanding of soil biochemical processes and thus help us to develop sound management strategies. The objective of this study was to investigate the effects of long-term fertilization regimes on soil microbial community functional diversity, metabolic activity, and metabolic quotient and to find out the main factors that influence these parameters. A long-term fertilization experiment established in a sandy loam soil at northern China has received continuous fertilization treatments for more than 20 years, including control, mineral fertilizers of NK, PK, NP, and NPK, organic amendment (OA), and half organic amendment plus half mineral fertilizer (1/2 OM). Top soil samples (0–15 cm) from four individual plots per treatment were collected for the analysis of chemical properties and microbial parameters. Microbial biomass C was analyzed using the fumigation–extraction method. Invertase activity and basal respiration were determined based on incubation method. Then, the microbial metabolic quotient was calculated as the ratio of basal respiration to microbial biomass C. To this end, microbial functional diversity was evaluated using the community level physiological profile method by Biolog Eco-microplate. Higher microbial biomass C, invertase activity, and basal respiration, but lower microbial metabolic quotient, were observed in P-fertilized soils, and OA had significantly greater (P < 0.05) impacts on the biomass, activity, and quotient compared with mineral fertilizers. Both the sole-carbon-source utilization activity and the functional diversity of soil microbial community were significantly increased (P < 0.05) by balanced fertilization (NPK, OA, or 1/2 OM), and species richness of community and relative abundance of the most common species in the K-deficient (NP) treatment were also significantly increased (P < 0.05). Principal component analysis and redundancy analysis showed that both organic and mineral fertilizers could affect microbial parameters by increasing soil organic C contents, and P was the key factor to increase soil microbial diversity and soil fertility. Long-term balanced fertilization greatly increased soil microbial biomass, functional diversity, and invertase activity and played an important role in decreasing soil microbial metabolic quotient, while P could be considered as the key factor to control soil microbial diversity as well as soil fertility. With regard to the different effects of OA and mineral fertilizer on soil organic C contents and root exudates, combined application of mineral and organic fertilizers is recommended in the region.

Microbial functional diversity, metabolic quotient, and invertase activity of a sandy loam soil as affected by long-term application of organic amendment and mineral fertilizer

Lettuce and rhizosphere microbiome responses to growth promoting Pseudomonas species under field conditions

Comparison of microbial activity in some Brazilian soils by microcalorimetric and respirometric methods

Calorimetry versus respirometry for the monitoring of microbial activity in a tropical soil

Comparison between microorganism counting and a calorimetric method applied to tropical soils

A pesquisa sobre bacterias diazotroficas na cultura do trigo tem demonstrado a necessidade de associar bacterias eficientes a genotipos promissores, os quais se beneficiariam dessa associacao. Em um experimento com parcelas subdivididas, instalado em condicoes de campo, em Mococa (SP), empregando os tratamentos: tres doses de N (0, 60 e 120 kg ha-1) e tres genotipos de trigo (IAC-24, ITD-19 e IAC-355), foi avaliada a ocorrencia de microrganismos diazotroficos endofiticos em raizes desinfestadas superficialmente, utilizando-se tres meios de cultivo distintos, NFb, JNFb e LGI-P. Somente para o genotipo IAC-355, houve um ajuste linear ascendente da quantidade de bacterias diazotroficas com o aumento na quantidade de N adicionada, apesar de o mesmo genotipo apresentar o menor numero de bacterias diazotroficas endofiticas nos tres meios de cultivo utilizados para quantificacao. Foram obtidos oito isolados bacterianos do meio NFb com as caracteristicas de Azospirillum e doze do meio JNFb com as caracteristicas de Herbaspirillum. Esses isolados foram testados "in vitro", nos genotipos dos quais foram originalmente isolados, ou seja, ITD-19 e IAC-24. Todos os isolados testados no genotipo ITD-19 causaram maior crescimento radicular que a testemunha e apenas um isolado do meio JNFb propiciou aumento significativo do N acumulado na parte aerea. A interacao planta-bacteria diazotrofica associativa indicou que e possivel obter beneficios desta associacao.

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Sueli dos Santos Freitas

Papers

Lettuce and rhizosphere microbiome responses to growth promoting Pseudomonas species under field conditions

Comparison of microbial activity in some Brazilian soils by microcalorimetric and respirometric methods

Calorimetry versus respirometry for the monitoring of microbial activity in a tropical soil

Comparison between microorganism counting and a calorimetric method applied to tropical soils

Ocorrência e efeito de bactérias diazotróficas em genótipos de trigo