A SIMPLE METHOD for DEMONSTRATING the PRODUCTION of GAS by BACTERIA

Sugar-seeking insects as a source of diverse bread-making yeasts with enhanced attributes

Insects represent a particularly interesting habitat in which to search for novel yeasts of value to industry. Insect-associated yeasts have the potential to have traits relevant to modern food and beverage production due to insect-yeast interactions, with such traits including diverse carbohydrate metabolisms, high sugar tolerance, and general stress tolerance. Here, we consider the potential value of insect-associated yeasts in the specific context of baking. We isolated 63 yeast strains from 13 species of hymenoptera from the United States, representing 37 yeast species from 14 genera. Screening for the ability to ferment maltose, a sugar important for bread production, resulted in the identification of 13 strains of Candida, Lachancea, and Pichia species. We assessed their ability to leaven dough. All strains produced baked loaves comparable to a commercial baking strain of Saccharomyces cerevisiae. The same 13 strains were also grown under various sugar and salt conditions relevant to osmotic challenges experienced in the manufacturing processes and the production of sweet dough. We show that many of these yeast strains, most notably strains of Lachancea species, grow at a similar or higher rate and population size as commercial baker's yeast. We additionally assessed the comparative phenotypes and genetics of insect-associated S. cerevisiae strains unable to ferment maltose and identified baking-relevant traits, including variations in the HOG1 signaling pathway and diverse carbohydrate metabolisms. Our results suggest that non-conventional yeasts have high potential for baking and, more generally, showcase the success of bioprospecting in insects for identifying yeasts relevant for industrial uses.

Microbiota Assessments for the Identification and Confirmation of Slit Defect-Causing Bacteria in Milk and Cheddar Cheese

Food production involves numerous control points for microorganisms to ensure quality and safety. These control points (e.g., pasteurization) are difficult to develop for fermented foods wherein some microbial contaminants are also expected to provide positive contributions to the final product and spoilage microbes may constitute only a small proportion of all microorganisms present.

Validated methods are needed to detect spoilage microbes present in low numbers in foods and ingredients prior to defect onset. We applied propidium monoazide combined with 16S rRNA gene sequencing, qPCR, isolate identification, and pilot-scale cheese making to identify the microorganisms that cause slit defects in industrially produced Cheddar cheese. To investigate milk as the source of spoilage microbes, bacterial composition in milk was measured immediately before and after high-temperature, short-time (HTST) pasteurization over 10-h periods on 10 days and in the resulting cheese blocks. Besides HTST pasteurization-induced changes to milk microbiota composition, a significant increase in numbers of viable bacteria was observed over the 10-h run times of the pasteurizer, including 68-fold-higher numbers of the genus Thermus. However, Thermus was not associated with slit development. Milk used to make cheese which developed slits instead contained a lower number of total bacteria, higher alpha diversity, and higher proportions of Lactobacillus, Bacillus, Brevibacillus, and Clostridium. Only Lactobacillus proportions were significantly increased during cheese aging, and Limosilactobacillus (Lactobacillus) fermentum, in particular, was enriched in slit-containing cheeses and the pre- and post-HTST-pasteurization milk used to make them. Pilot-scale cheeses developed slits when inoculated with strains of L. fermentum, other heterofermentative lactic acid bacteria, or uncultured bacterial consortia from slit-associated pasteurized milk, thereby confirming that low-abundance taxa in milk can negatively affect cheese quality. The likelihood that certain microorganisms in milk cause slit defects can be predicted based on comparisons of the bacteria present in the milk used for cheese manufacture.

IMPORTANCE Food production involves numerous control points for microorganisms to ensure quality and safety. These control points (e.g., pasteurization) are difficult to develop for fermented foods wherein some microbial contaminants are also expected to provide positive contributions to the final product and spoilage microbes may constitute only a small proportion of all microorganisms present. We showed that microbial composition assessments with 16S rRNA marker gene DNA sequencing are sufficiently robust to detect very-low-abundance bacterial taxa responsible for a major but sporadic Cheddar cheese spoilage defect. Bacterial composition in the (pasteurized) milk and cheese was associated with slit defect development. The application of Koch’s postulates showed that individual bacterial isolates as well as uncultured bacterial consortia were sufficient to cause slits, even when present in very low numbers. This approach may be useful for detection and control of low-abundance spoilage microorganisms present in other foods.

A short history of methods used to measure bathing beach water quality

The enumeration of fecal indicators of bathing beach water to determine quality have been used since the mid-20th century. In the 1930s and as late the 1970s, the Most Probable Number procedure for estimating microbial densities in water was in general use. The most probable number procedure was replaced as a method of choice by the membrane filter procedure. The membrane filter had been developed in the early 1950s but did not find widespread use until the 1970s. Another development during the 1970s was the quanti -tray method, a proprietary multi-well tray, which was introduced as an innovative form of the Most Probable Number procedure. In 2005 molecular methods were introduced as a rapid 3-hourh procedure for measuring bathing beach water quality. Several variations of this approach are currently in use or in development.

Multi-Drug Resistant Coliform: Water Sanitary Standards and Health Hazards

Water constitutes and sustains life; however, its pollution afflicts its necessity, further worsening its scarcity. Coliform is one of the largest groups of bacteria evident in fecally polluted water, a major public health concern. Coliform thrive as commensals in the gut of warm-blooded animals, and are indefinitely passed through their feces into the environment. They are also called as model organisms as their presence is indicative of the prevalence of other potential pathogens, thus coliform are and unanimously employed as adept indicators of fecal pollution. As only a limited accessible source of fresh water is available on the planet, its contamination severely affects its usability. Coliform densities vary geographically and seasonally which leads to the lack of universally uniform regulatory guidelines regarding water potability often leads to ineffective detection of these model organisms and the misinterpretation of water quality status. Remedial measures such as disinfection, reducing the nutrient concentration or re-population doesn’t hold context in huge lotic ecosystems such as freshwater rivers. There is also an escalating concern regarding the prevalence of multi-drug resistance in coliforms which renders antibiotic therapy incompetent. Antimicrobials are increasingly used in household, clinical, veterinary, animal husbandry and agricultural settings. Sub-optimal concentrations of these antimicrobials are unintentionally but regularly dispensed into the environment through seepages, sewages or runoffs from clinical or agricultural settings substantially adding to the ever-increasing pool of antibiotic resistance genes. When present below their minimum inhibitory concentration (MIC), these antimicrobials trigger the transfer of antibiotic-resistant genes that the coliform readily assimilate and further propagate to pathogens, the severity of which is evidenced by the high Multiple Antibiotic Resistance (MAR) index shown by the bacterial isolates procured from the environmental. This review attempts to assiduously anthologize the use of coliforms as water quality standards, their existent methods of detection and the issue of arising multi-drug resistance in them.

Hydrogen sulfide in physiology and pathogenesis of bacteria and viruses

An increasing number of studies have established hydrogen sulfide (H₂S) gas as a major cytoprotectant and redox modulator. Following its discovery, H₂S has been found to have pleiotropic effects on physiology and human health. H₂S acts as a gasotransmitter and exerts its influence on gastrointestinal, neuronal, cardiovascular, respiratory, renal, and hepatic systems. Recent discoveries have clearly indicated the importance of H₂S in regulating vasorelaxation, angiogenesis, apoptosis, ageing, and metabolism. Contrary to studies in higher organisms, the role of H₂S in the pathophysiology of infectious agents such as bacteria and viruses has been less studied. Bacterial and viral infections are often accompanied by changes in the redox physiology of both the host and the pathogen. Emerging studies indicate that bacterial-derived H₂S constitutes a defense system against antibiotics and oxidative stress. The H₂S signaling pathway also seems to interfere with redox-based events affected on infection with viruses. This review aims to summarize recent advances on the emerging role of H₂S gas in the bacterial physiology and viral infections. Such studies have opened up new research avenues exploiting H₂S as a potential therapeutic intervention.

A timeline of hydrogen sulfide (H2S) research: From environmental toxin to biological mediator

The history of H2S - as an environmental toxin - dates back to 1700, to the observations of the Italian physician Bernardino Ramazzini, whose book "De Morbis Artificum Diatriba" described the painful eye irritation and inflammation of "sewer gas" in sewer workers. The gas has subsequently been identified as hydrogen sulfide (H2S), and opened three centuries of research into the biological roles of H2S. The current article highlights the key discoveries in the field of H2S research, including (a) the toxicological studies, which characterized H2S as an environmental toxin, and identified some of its modes of action, including the inhibition of mitochondrial respiration; (b) work in the field of bacteriology, which, starting in the early 1900s, identified H2S as a bacterial product - with subsequently defined roles in the regulation of periodontal disease (oral bacterial flora), intestinal epithelial cell function (enteral bacterial flora) as well as in the regulation of bacterial resistance to antibiotics; and (c), work in diverse fields of mammalian biology, which, starting in the 1940s, identified H2S as an endogenous mammalian enzymatic product, the functions of which - among others, in the cardiovascular and nervous system - have become subjects of intensive investigation for the last decade. The current review not only enumerates the key discoveries related to H2S made over the last three centuries, but also compiles the most frequently cited papers in the field which have been published over the last decade and highlights some of the current 'hot topics' in the field of H2S biology.

Screening and characterization of amylase and cellulase activities in psychrotolerant yeasts

Background

Amylases and cellulases have great potential for application in industries such as food, detergent, laundry, textile, baking and biofuels. A common requirement in these fields is to reduce the temperatures of the processes, leading to a continuous search for microorganisms that secrete cold-active amylases and cellulases. Psychrotolerant yeasts are good candidates because they inhabit cold-environments. In this work, we analyzed the ability of yeasts isolated from the Antarctic region to grow on starch or carboxymethylcellulose, and their potential extracellular amylases and cellulases.

Result

All tested yeasts were able to grow with soluble starch or carboxymethylcellulose as the sole carbon source; however, not all of them produced ethanol by fermentation of these carbon sources. For the majority of the yeast species, the extracellular amylase or cellulase activity was higher when cultured in medium supplemented with glucose rather than with soluble starch or carboxymethylcellulose. Additionally, higher amylase activities were observed when tested at pH 5.4 and 6.2, and at 30–37 °C, except for Rhodotorula glacialis that showed elevated activity at 10–22 °C. In general, cellulase activity was high until pH 6.2 and between 22–37 °C, while the sample from Mrakia blollopis showed high activity at 4–22 °C. Peptide mass fingerprinting analysis of a potential amylase from Tetracladium sp. of about 70 kDa, showed several peptides with positive matches with glucoamylases from other fungi.

Conclusions

Almost all yeast species showed extracellular amylase or cellulase activity, and an inducing effect by the respective substrate was observed in a minor number of yeasts. These enzymatic activities were higher at 30 °C in most yeast, with highest amylase and cellulase activity in Tetracladium sp. and M. gelida, respectively. However, Rh. glacialis and M. blollopis displayed high amylase or cellulase activity, respectively, under 22 °C. In this sense, these yeasts are interesting candidates for industrial processes that require lower temperatures.

Electronic supplementary material

The online version of this article (doi:10.1186/s12866-016-0640-8) contains supplementary material, which is available to authorized users.

SlyD-dependent nickel delivery limits maturation of [NiFe]-hydrogenases in late-stationary phase Escherichia coli cells

Fermentatively growing Escherichia coli cells have three active [NiFe]-hydrogenases (Hyd), two of which, Hyd-1 and Hyd-2, contribute to H2 oxidation while Hyd-3 couples formate oxidation to H2 evolution. Biosynthesis of all Hyd involves the insertion of a Fe(CN)2CO group and a subsequent insertion of nickel ions through the HypA/HybF, HypB and SlyD proteins. With high nickel concentrations the presence of none of these proteins is required, but under normal growth conditions and during late stationary growth SlyD is important for hydrogenase activities. The slyD mutation reduced H2 production during exponential phase growth by about 50%. Assaying stationary phase grown cells for the coupling of Hyd activity to the respiratory chain or formate-dependent H2 evolution showed that SlyD is essential for both H2 evolution and H2 oxidation. Although introduction of plasmid-coded slyD resulted in an overall decrease of Hyd-2 polypeptides in slyD and hypA slyD mutants, processing and dye-reducing activity of the Hyd-2 enzyme was nevertheless restored. Similarly, introduction of the slyD plasmid restored only some H2 evolution in the slyD mutant while Hyd-3 polypeptides and dye-reducing activity were fully restored. Taken together, these results indicate an essential role for SlyD in the generation of the fully cofactor-equipped hydrogenase large subunits in the stationary phase where the level of each Hyd enzyme is finely tuned by SlyD for optimal enzyme activity.

Lactose-Fermenting Bacteria in Faeces

The following experiments were begun with the object of ascertaining the distribution in nature of certain lactose-fermenting organisms which are by some grouped under the name Bacillus coli, but by others are regarded as belonging to a different class of organisms; a difference of opinion which is most probably the principal factor in causing the value of B. coli as an index of pollution to be such a vexed question among bacteriologists. The investigation, however, resolved itself into a search for the B. lactis aerogenes principally, and secondarily for the other lactose fermenters. Incidentally certain other points are referred to which it was thought might prove of interest though not actually pertaining to the subject of the paper.

B. coli as an Index of Faecal Pollution of Water Supplies

The present investigation deals with the routine bacteriological examination of 525 samples of water, 265 of which contained lactose fermenting bacilli; 1441 strains were isolated and various differential tests were used in the classification of these organisms.

All the strains were tested in dextrose phosphate culture for the methyl red and the Voges and Proskauer reactions, and although most of them gave normal results (M.R. + V.P. 0 or M.R. 0 V.P. +), there were 25 strains, 1·73 per cent., which gave either double positive or double negative reactions. Similar cases have already been discussed in an earlier portion of this paper, and they leave no doubt that there are types which may vary from the normal as far as the methyl red and the Voges and Proskauer reactions are concerned. At the same time these abnormal types are not sufficiently numerous to make any real practical difficulties in the use of these tests for routine purposes.

The Koser test, considered by many bacteriologists to be of great differential value, was found to give imperfect correlation with the other reactions.

1395 strains were isolated which could be classified in theB. coligroup as a result of the production of acid and gas in lactose, the clotting of milk, and the non-liquefaction of gelatine, but when the methyl red and the Voges and Proskauer results were considered it was found that nearly 11 per cent. of these strains were of theB. lactis aerogenestype, and were therefore of no value as indicators of faecal pollution.

The indol reactions were somewhat variable. Among 1244 strains of theB. colitype (M.R. + V.P. 0), more than 10 per cent. failed to produce indol; while among 151 strains of theB. lactis aerogenestype (M.R. 0 V.P. +), nearly 51 per cent. were indol producers. Preliminary extraction with ether was carried out with 448 of these strains before Böhme's reagent was added. With this technique it was found that among 400 methyl red positive types there were 87 strains (22 per cent.) which produced no indol, and among 48 methyl red negative strains there were 12 (25 per cent.) which gave the reaction. Chen and Rettger (1920) were unable to establish any definite correlation between the indol test and the other reactions.

When the sample results were studied, it was found that although 262 waters contained organisms which were included in theB. coligroup on the basis of the lactose, milk and gelatine tests, nearly 6 per cent. of these samples contained only organisms which gave a methyl red negative, Voges and Proskauer positive reaction, and were probably associated with pollution from soil washings rather than contamination from faecal sources. This means that the application of the methyl red and Voges and Proskauer reaction does make a considerable practical difference in the interpretation of results in the bacteriological examination of water.

More detailed examination as regards the fermentation of the various carbohydrates is useful for purposes of classification, but is of no significance, in the light of our present knowledge, in assessing the probability of excretal pollution.

It is suggested that, in considering the results of a bacteriological examination of water, organisms should be regarded as significant which are of typical morphology and staining reaction, produce acid and gas in lactose, fail to liquefy gelatine, clot milk, and give a positive methyl red and a negative Voges and Proskauer reaction. The production of indol in a medium containing peptone may be added as an extra test if desired, but the available evidence does not suggest that failure to produce indol is a sufficient basis for the exclusion of an otherwise typical bacillus from theB. coligroup.

My thanks are due to Dr G. D. Dawson, in conjunction with whom the present investigation was started; and also to Prof. W. W. C. Topley whose interest throughout the course of the research was made manifest by his helpful advice and criticism.

The Classification of the Colon-Aerogenes Group of Bacteria in Relation to their Habitat and its Application to the Sanitary Examination of Water Supplies in the Tropics and in Temperate Climates: A Comparative Study of 2500 Cultures

(1) The ”lactose+ indol+” index as employed in temperate climate is usually an adequate criterion of water purity.

(2) Where a positive test does not appear to be substantiated by the sanitary findings, a further differentiation of the organisms isolated becomes necessary. The methyl-red and citrate tests have been found to supply that differentiation in a satisfactory manner.

(3) In the Tropics, false positive “lactose-indol” tests are commonly encountered, owing to the presence in large numbers in soil and water of organisms derived from sources other than recently excreted faeces.

(4) In the Tropics, the lactose-indol test should always be confirmed by the methyl-red, citrate and saccharose tests or such other reactions or groups of reactions as may be found by a local survey to be applicable.

My very grateful thanks are due to Dr P. A. Clearkin, Deputy Director of Laboratory Service, Tanganyika Territory, for his ready advice and constant encouragement; and also to Mr W. Whitley, Analytical Chemist, who performed a chemical analysis of the water samples, and very kindly gave me the benefit of his opinion on them. In addition I have to thank Dr R. R. Scott, Medical Officer of Health, and the Staff of the Health Office, Dar-es-Salaam, who have rendered every facility in the choice and collection of samples. It is a pleasure to be able to record once more my indebtedness to Prof. Bigger, of Trinity College, Dublin, whose fund of valuable suggestions and kindly criticism has been ever at my disposal.

The characterization of the rumen bacterium Eadie's oval, Magnoovum gen. nov. eadii sp. nov

The rumen bacterium Eadie's Oval was examined by means of cell wall analysis and biochemical tests with a view to determine its taxonomic position. The purified cell walls contained components consistent with the organism being a Gram-negative bacterium, and despite its large size no abnormal cell wall constituents were found. The biochemical tests indicate that Eadie's Oval is not a member of a previously described family. The name Magnoovum gen. nov. eadii sp. nov. is proposed.

The lactose system in Klebsiella aerogenes V9A. 1. Characteristics of two lac mutant phenotypes which revert to wild-type

A wild strain of Klebsiella aerogenes (V9A), which contains a plasmid Fklac carrying the genes of the lac operon, gives two mutant cell types, recognized by the appearance of their colonies on MacConkey lactose agar. These are referred to as ML− and ML−/+, wild-type being ML+. ML− cells can grow rapidly on 1% lactose as carbon source but very slowly on 0·2% unless induced by TMG or D-fucose, or by previous growth on galactose, melibiose or raffinose, which enables them to grow rapidly on 0·2% lactose for 2–4 cell generations. Previous growth on 1% lactose does not induce the ability to grow rapidly on 0·2% lactose. It is concluded that ML− cells have a defect in the lactose permease gene which allows slow uptake of lactose when the external concentration is 0·2% and more rapid uptake when the external concentration is increased. In addition, TMG, D-fucose, galactose, melibiose and raffinose induce one or more other galactoside permeases which can accumulate lactose efficiently but are not induced by lactose. ML−/+ cells can grow normally on 0·2% lactose as carbon source, but only after a substantial lag when transferred from glucose, glycerol or sucrose, and after an even longer lag when transferred from melibiose or raffinose. Wild-type cells (ML+) grow normally on 0·2% lactose after a short lag of less than a cell generation time, when transferred from any other carbon source. Cells of each of the three phenotypes (+, −/+ and −) can mutate to give both of the other two phenotypes. Incomplete genetic evidence suggests that the ML− mutation is a result of a reversible change in the Fklac plasmid.

Rapid procedure for the detection of acid and gas production by bacterial cultures

A rapid miniaturized procedure, with a Microtiter plate and the Amojell-overlay technique, is described for the detection of acid and gas production by bacterial cultures.