The ability of acidic pH, growth inhibitors, and glucose to increase the proton motive force and energy spilling of amino acid-fermenting Clostridium sporogenes MD1 cultures

Regulating alternative lifestyles in entomopathogenic bacteria

Bacteria belonging to the genera Photorhabdus and Xenorhabdus participate in a trilateral symbiosis in which they enable their nematode hosts to parasitize insect larvae. The bacteria switch from persisting peacefully in a nematode's digestive tract to a lifestyle in which pathways to produce insecticidal toxins, degrading enzymes to digest the insect for consumption, and antibiotics to ward off bacterial and fungal competitors are activated. This study addresses three questions: (1) What molecular signal triggers antibiotic production in the bacteria? (2) What small molecules are regulated by the signal? And (3), how do the bacteria recognize the signal? Differential metabolomic profiling in Photorhabdus luminescens TT01 and Xenorhabdus nematophila revealed that L-proline in the insect's hemolymph initiates a metabolic shift. Small molecules known to be crucial for virulence and antibiosis in addition to previously unknown metabolites are dramatically upregulated by L-proline, linking the recognition of host environment to bacterial metabolic regulation. To identify the L-proline-induced signaling pathway, we deleted the proline transporters putP and proU in P. luminescens TT01. Studies of these strains support a model in which acquisition of L-proline both regulates the metabolic shift and maintains the bacterial proton motive force that ultimately regulates the downstream bacterial pathways affecting virulence and antibiotic production.

The antimicrobial effects of hops (Humulus lupulus L.) on ruminal hyper ammonia-producing bacteria

AIM

To assess the antimicrobial effects of hops (Humulus lupulus L.) on hyper ammonia producing-bacteria (HAB), which catabolize amino acids and peptides in the bovine rumen.

METHODS AND RESULTS

When media were amended with dried hops or hops extract (30.7% lupulone), ammonia production by mixed rumen bacteria was inhibited. The growth and ammonia production of pure cultures (Peptostreptococcus anaerobius, Clostridium aminophilum, or Clostridium sticklandii) was inhibited by 30 ppm lupulone at pH 6.7, and bactericidal activity was observed at pH 5.6. When hops extract was added to energized cell suspensions, the intracellular pH rapidly decreased and intracellular potassium was lost.

CONCLUSIONS

The three HAB species were sensitive to the antimicrobial components in hops, and the inhibition of ammonia production by mixed rumen bacteria indicates that similar effects could be expected in the rumen.

SIGNIFICANCE AND IMPACT OF THE STUDY

As much as half of the amino acids consumed by ruminants can be lost due to microbial degradation in the rumen. This study supports the idea that biologically active plant metabolites can be used to mitigate this wasteful process.

The energy spilling reactions of bacteria and other organisms

For many years it was assumed that living organisms always utilized ATP in a highly efficient manner, but simple growth studies with bacteria indicated that the efficiency of biomass production was often at least 3-fold lower than the amount that would be predicted from standard biosynthetic pathways. The utilization of energy for maintenance could only explain a small portion of this discrepancy particularly when the growth rate was high. These ideas and thermodynamic arguments indicated that cells might have another avenue of energy utilization. This phenomenon has also been called 'uncoupling', 'spillage' and 'overflow metabolism', but 'energy spilling' is probably the most descriptive term. It appears that many bacteria spill energy, and the few that do not can be killed (large and often rapid decrease in viability), if the growth medium is nitrogen-limited and the energy source is in 'excess'. The lactic acid bacterium, Streptococcus bovis, is an ideal bacterium for the study of energy spilling. Because it only uses substrate level phosphorylation to generate ATP, ATP generation can be calculated with a high degree of certainty. It does not store glucose as glycogen, and its cell membrane can be easily accessed. Comparative analysis of heat production, membrane voltage, ATP production and Ohm's law indicated that the energy spilling reaction of S. bovis is mediated by a futile cycle of protons through the cell membrane. Less is known about Escherichia coli, but in this bacterium energy spilling could be mediated by a futile cycle of potassium or ammonium ions. Energy spilling is not restricted to prokaryotes and appears to occur in yeasts and in higher organisms. In man, energy spilling may be related to cancer, ageing, ischemia and cardiac failure.

Bacterial diversity of an acidic Louisiana groundwater contaminated by dense nonaqueous-phase liquid containing chloroethanes and other solvents

Bacterial concentration and diversity was assessed in a moderately acidic (pH 5.1) anaerobic groundwater contaminated by chlorosolvent-containing DNAPL at a Superfund site located near Baton Rouge, Louisiana. Groundwater analysis revealed a total aqueous-phase chlorosolvent concentration exceeding 1000 mg L(-1), including chloroethanes, vinyl chloride, 1,2-dichloropropane, and hexachloro-1,3-butadiene as the primary contaminants. Direct counting of stained cells revealed more than 3 x 10(7) cells mL(-1) in the groundwater, with 58% intact and potentially viable. Universal and 'Dehalococcoides'-specific 16S rRNA gene libraries were created and analyzed. Universal clones were grouped into 18 operational taxonomic units (OTUs), which were dominated by low-G+C Gram-positive bacteria (62%) and included several as yet uncultured or undescribed organisms. Several unique 16S rRNA gene sequences closely related to Dehalococcoides ethenogenes were detected. Anaerobically grown isolates (168 in total) were also sequenced. These were phylogenetically grouped into 18 OTUs, of which only three were represented in the clone library. Phylogenetic analysis of isolates and the clone sequences revealed close relationships with dechlorinators, fermenters, and hydrogen producers. Despite acidic conditions and saturation or near-saturation chlorosolvent concentrations, the data presented here demonstrate that large numbers of novel bacteria are present in groundwater within the DNAPL source zone, and the population appears to contain bacterial components necessary to carry out reductive dechlorination.

Fermentation acids inhibit amino acid deamination by Clostridium sporogenes MD1 via a mechanism involving a decline in intracellular glutamate rather than protonmotive force

Fermentation acids inhibited the growth and ammonia production of the amino-acid-fermenting bacterium Clostridium sporogenes MD1, but only when the pH was acidic. Such inhibition was traditionally explained by the ability of fermentation acids to act as uncouplers and decrease protonmotive force (Deltap), but C. sporogenes MD1 grows even if the Deltap is very low. Cell suspensions incubated with additional sodium chloride produced ammonia as rapidly at pH 5.0 as at pH 7.0, but cells incubated with additional sodium lactate were sensitive to even small decreases in extracellular pH. Similar results were obtained if the sodium lactate was replaced by sodium acetate or propionate. When extracellular pH declined, DeltapH increased even if sodium lactate was present. The cells accumulated intracellular lactate anion when the pH was acidic, and intracellular glutamate declined. Because amino acid deamination is linked to a transamination reaction involving glutamate dehydrogenase, the decrease in ammonia production could be explained by the decrease in intracellular glutamate. This latter hypothesis was consistent with the observation that extracellular glutamate addition restored amino acid deamination even though glutamate alone did not allow for the generation of ammonia.