Intake of different types of dairy and its prospective association with risk of type 2 diabetes: The Rotterdam Study.

BACKGROUND AND AIMS: The prevalence of type 2 diabetes (T2DM) is increasing. Several studies have suggested a beneficial effect of several major dairy nutrients on insulin production and sensitivity. Conversely, harmful effects have been suggested as well. This study aimed to investigate the impact of the full-range of dairy products and its association with incidence T2DM in Dutch adults aged ≥55 years participating in the Rotterdam Study. METHODS AND RESULTS: Dairy intake was assessed with a validated FFQ, including total, skimmed, semi-skimmed, full-fat, fermented, and non-fermented dairy, and subclasses of these product groups. Verified prevalent and incident diabetes were documented. Cox proportional hazards regression and spline regression were used to analyse data, adjusting for age, sex, alcohol, smoking, education, physical activity, body mass index, intake of total energy, energy-adjusted meat, and energy-adjusted fish intake. Median total dairy intake was 398 g/day (IQR 259-559 g/day). Through 9.5 ± 4.1 years of follow-up, 393 cases of incident T2DM were reported. Cox and spline regression did not point towards associations of total dairy consumption, dairy consumption based on fat content, non-fermented or fermented dairy consumption, or individual dairy product consumption with incident T2DM. The HR for total dairy intake and T2DM was 0.93 (95% CI: 0.70-1.23) in the upper quartile (P-for trend 0.76). CONCLUSIONS: This prospective cohort study did not point towards an association between dairy consumption and T2DM.

Metabolic interactions between methanogenic consortia and anaerobic respiring bacteria.

Most types of anaerobic respiration are able to outcompete methanogenic consortia for common substrates if the respective electron acceptors are present in sufficient amounts. Furthermore, several products or intermediate compounds formed by anaerobic respiring bacteria are toxic to methanogenic consortia. Despite the potentially adverse effects, only few inorganic electron acceptors potentially utilizable for anaerobic respiration have been investigated with respect to negative interactions in anaerobic digesters. In this chapter we review competitive and inhibitory interactions between anaerobic respiring populations and methanogenic consortia in bioreactors. Due to the few studies in anaerobic digesters, many of our discussions are based upon studies of defined cultures or natural ecosystems.

Anaerobic conversion of lactic acid to acetic acid and 1, 2-propanediol by Lactobacillus buchneri.

The degradation of lactic acid under anoxic conditions was studied in several strains of Lactobacillus buchneri and in close relatives such as Lactobacillus parabuchneri, Lactobacillus kefir, and Lactobacillus hilgardii. Of these lactobacilli, L. buchneri and L. parabuchneri were able to degrade lactic acid under anoxic conditions, without requiring an external electron acceptor. Each mole of lactic acid was converted into approximately 0.5 mol of acetic acid, 0.5 mol of 1,2-propanediol, and traces of ethanol. Based on stoichiometry studies and the high levels of NAD-linked 1, 2-propanediol-dependent oxidoreductase (530 to 790 nmol min(-1) mg of protein(-1)), a novel pathway for anaerobic lactic acid degradation is proposed. The anaerobic degradation of lactic acid by L. buchneri does not support cell growth and is pH dependent. Acidic conditions are needed to induce the lactic-acid-degrading capacity of the cells and to maintain the lactic-acid-degrading activity. At a pH above 5.8 hardly any lactic acid degradation was observed. The exact function of anaerobic lactic acid degradation by L. buchneri is not certain, but some results indicate that it plays a role in maintaining cell viability.

The impact of the quality of silage on animal health and food safety: a review.

This paper reviews the microbiological aspects of forage preserved by ensilage. The main principles of preservation by ensilage are a rapid achievement of a low pH by lactic acid fermentation and the maintenance of anaerobic conditions. The silage microflora consists of beneficial micro-organisms, i.e. the lactic acid bacteria responsible for the silage fermentation process, and a number of harmful micro-organisms that are involved in anaerobic or aerobic spoilage processes. Micro-organisms that can cause anaerobic spoilage are enterobacteria and clostridia. Clostridium tyrobutyricum is of particular importance because of its ability to use lactic acid as a substrate. Silage-derived spores of C. tyrobutyricum can cause problems in cheese making. Aerobic spoilage of silage is associated with penetration of oxygen into the silage during storage or feeding. Lactate-oxidizing yeasts are generally responsible for the initiation of aerobic spoilage. The secondary aerobic spoilage flora consists of moulds, bacilli, listeria, and enterobacteria. Mycotoxin-producing moulds, Bacillus cereus, and Listeria monocytogenes in aerobically deteriorated silage form a serious risk to the quality and safety of milk and to animal health.

Desulfobacca acetoxidans gen. nov., sp. nov., a novel acetate-degrading sulfate reducer isolated from sulfidogenic granular sludge.

A mesophilic sulfate reducer, strain ASRB2T, was isolated with acetate as sole carbon and energy source from granular sludge of a laboratory-scale upflow anaerobic sludge bed reactor fed with acetate and sulfate. The bacterium was oval-shaped, 1.3 x 1.9-2.2 microns, non-motile and Gram-negative. Optimum growth with acetate occurred around 37 degrees C in freshwater medium (doubling time: 1.7-2.2 d). Enzyme studies indicated that acetate was oxidized via the carbon monoxide dehydrogenase pathway. Growth was not supported by other organic acids, such as propionate, butyrate or lactate, alcohols such as ethanol or propanol, and hydrogen or formate. Sulfite and thiosulfate were also used as electron acceptors, but sulfur and nitrate were not reduced. Phylogenetically, strain ASRB2T clustered with the delta subclass of the Proteobacteria. Its closest relatives were Desulfosarcina variabilis, Desulfacinum infernum and Syntrophus buswellii. Strain ASRB2T is described as the type strain of Desulfobacca acetoxidans gen. nov., sp. nov.

Detection and quantification of microorganisms in anaerobic bioreactors.

The presence of sulfate in anaerobic reactors can trigger competitive and syntrophic interactions between various groups of microorganisms, such as sulfate reducers, methanogens and acetogens. In order to steer the reactor process in the direction of sulfidogenesis or methanogenesis, it is essential to get insight into the population dynamics of these groups of microorganisms upon changes in the reactor operating conditions. Several methods exist to characterize and quantify the microbial sludge composition. Combining classical microbiological and modern molecular-based sludge characterization methods has proven to be a powerful approach to study the microbial composition of the anaerobic sludge.

Understanding and advancing wastewater treatment.

In bioreactors used for the purification of wastewater, microorganisms are active in biofilms or aggregates. Insight into the factors that determine the structure and function of aggregated biomass is increasing steadily. Besides conventional techniques, modem molecular techniques are used increasingly to get a better understanding of the complex microbial communities in wastewater treatment systems. In recent years, the combined use of these techniques has led to a good insight into the population dynamics of different types of microbes in bioreactors.

Desulforhabdus amnigenus gen. nov. sp. nov., a sulfate reducer isolated from anaerobic granular sludge.

From granular sludge of an upflow anaerobic sludge bed (UASB) reactor treating paper-mill wastewater, a sulfate-reducing bacterium (strain ASRB1) was isolated with acetate as sole carbon and energy source. The bacterium was rod-shaped, (1.4-1.9 x 2.5-3.4 microns), nonmotile, and gram-negative. Optimum growth with acetate occurred around 37 degrees C in freshwater medium (doubling time: 3.5-5.0 days). The bacterium grew on a range of organic acids, such as acetate, propionate, and butyrate, and on alcohols, and grew autotrophically with H2, CO2, and sulfate. Fastest growth occurred with formate, propionate, and ethanol (doubling time: approx. 1.5 days). Strain ASRB1 clusters with the delta subdivision of Proteobacteria and is closely related to Syntrophobacter wolinii, a syntrophic propionate oxidizer. Strain ASRB1 was characterized as a new genus and species: Desulforhabdus amnigenus.

Xylose and Glucose Utilization by Bacteroides xylanolyticus X5-1 Cells Grown in Batch and Continuous Culture.

During cultivation on a mixture of xylose and glucose, Bacteroides xylanolyticus X5-1 showed neither diauxic growth nor a substrate preference. Xylose-limited continuous-culture cells were able to consume xylose and glucose both as single substrates and as mixed substrates without any lag phase. When glucose was the growth-limiting substrate, the microorganism was unable to consume xylose. However, in the presence of a small amount of glucose or pyruvate, xylose was utilized after a short lag phase. In glucose-limited cells, xylose isomerase was present at low activity but xylulose kinase activity could not be detected. On addition of a mixture of xylose and glucose, xylose isomerase was induced immediately and xylulose kinase was induced after about 30 min. The induction of the two enzymes was sensitive to chloramphenicol, showing de novo synthesis. Xylose uptake in glucose-grown cells was very low, but the uptake rate could be increased when incubated with a xylose-glucose mixture. The increase in the uptake rate was not affected by chloramphenicol, indicating that a constitutive uptake system had to be activated. The inability of B. xylanolyticus X5-1 cells undergoing glucose-limited continuous culture to induce the xylose catabolic pathway after the addition of only xylose probably was caused by energy limitation.