Reinaldo F. Gomez

Growth inhibition of Clostridium thermocellum by carboxylic acids: A mechanism based on uncoupling by weak acids

SummaryThe inhibition of Clostridium thermocellum strains by acetate and other organic acids (propionate, butyrate) can be explained by a model based on the chemiosmotic theory and uncoupler action. It is proposed that the charged permeant species in the process of anion exclusion is the dimer HA-2. Evidence for this mechanisms is provided by 31P-NMR studies of whole cells and cell extracts.

Activation of nitrosomorpholine and nitrosopyrrolidine to bacterial mutagens.

Abstract We have shown that nitrosomorpholine and nitrosopyrrolidine are metabolized by rat liver homogenates to mutagens active on Salmonella typhomurium . The resulting mutations seem to have been caused by base-pair substitutions and therefore are believed to be due to alkylations.

Heterotrophic nitrification by intestinal microorganisms

From studies of nitrate balance in man and analyses of fecal and ileostomy samples,8 the possibility that nitrite and nitrate are formed de novo in the intestine, possibly by heterotrophic nitrification has emerged. This proposition significantly alters our previous conceptions of mans exposure to nitrite and suggests that nitrite may play a role in the cause of intestinal cancer. Heterotrophic nitrification has been demonstrated in various microorganisms. Our work has shown that intestinal heterotrophic microbial isolates from man are able to oxidize nitrogenous compounds to nitrite. These isolates include both procaryotes and eucaryotes.

Conversion of acetohydroxamate and hydroxylamine to nitrite by intestinal microorganisms

SummaryWe have investigated the ability of intestinal microorganisms from the rat, guinea pig and man to carry out heterotrophic nitrification. We have shown that some intestinal isolates can oxidize acetohydroxamate and hydroxylamine to nitrite. Moreover, one of the isolates, Pseudomonas aeruginosa, exhibited the greatest nitrifying activity reported in the literature.

Characteristics of freeze-dried cells

Abstract Microorganisms have been found to be more sensitive to selective media after freeze-drying. This increased sensitivity can be measured and thus the degree of sublethal injury can be determined as a function of various processing variables. In light of this, the use of selective media for the enrichment and detection of pathogens in freeze-dried products has to be reevaluated; indeed, the literature is now becoming abundant with such evaluations. In addition, the response of freeze-dried microorganisms has been found to be dependent on the medium in which they were grown; the phenomena of “metabolic injury” and “minimal medium recovery” are observed when microorganisms are grown in a complete and minimal medium, respectively. The expression of these two phenomena also can be used to assay for injury. Observations on the effects of freeze-drying on cell viability lead to the conclusion that freeze-drying is a complex stress. Damage to the cellular membrane structure and function, RNA integrity, and, possibly, DNA have been cited. The extrapolation of these macromolecular changes to specific viability responses for the purpose of elucidating the principal site of damage is still difficult. It is our opinion that the pre- and post-freeze-drying conditions to which the microorganisms are exposed can lead to a situation in which a particular macromolecular damage can become dominant over others, depending on the physiology of the cell. This knowledge can not only be applied for the purpose of improving detection of undesirable microbes but also for the preservation of desirable cultures, such as starter cultures in the dairy industry. Finally, the finding that microorganisms leak or release nucleic acids after freeze-drying, as they do after freezing and heating, can be applied to the problem of elimination of undesirable cytoplasmic components of organisms to be used as protein sources (4, 8).

Use of Prokaryotic and Eukaryotic Culture Systems for Examining Biological Activity of Food Constituents

Microbial systems present a unique potential for biological monitoring of toxic constituents in foods and other materials, as well as the environment. As indicators of toxicity, they are comprehensive, rapid and reliable. They may also provide insight into the nature of the toxicity in question, for example mutagenic and genetic activities.