Academic literature on the topic 'Photobacterium angustum'

ABSTRACT Photobacterium species are members of the bacterial communities typically associated with scombrotoxin-forming fish. Reclassification and discovery of new Photobacterium species has caused confusion as to which species are capable of biogenic amine production. We analyzed histamine, cadaverine, and putrescine production by 104 Photobacterium strains representing 23 species. The presence of the genes for histidine decarboxylase (hdc), lysine decarboxylase (ldc), and ornithine decarboxylase (odc) was determined by real-time or conventional PCR and whole genome sequencing. Significant histamine production (>200 ppm) was detected in five Photobacterium species: P. angustum, P. aquimaris, P. kishitanii, P. damselae, and P. phosphoreum. The hdc gene was detected in all of these histamine-producing species except P. phosphoreum. Cadaverine was produced by eight Photobacterium species: P. angustum, P. aquimaris, P. damselae, P. iliopiscarium, P. kishitanii, P. leiognathi, P. mandapamensis, and P. phosphoreum. Putrescine was produced by six Photobacterium species: P. angustum, P. aquimaris, P. kishitanii, P. leiognathi, P. mandapamensis, and Photobacterium sp. Cadaverine production correlated closely with the presence of the ldc gene, but putrescine production did not correlate closely with the presence of the odc gene. Characterization of the biogenic amine production by Photobacterium species will allow identification of these marine bacteria and help ensure that current guidelines account for mitigation of these bacteria.

ABSTRACTScombrotoxin fish poisoning (SFP) remains the main contributor of fish poisoning incidents in the United States, despite efforts to control its spread. Psychrotrophic histamine-producing bacteria (HPB) indigenous to scombrotoxin-forming fish may contribute to the incidence of SFP. We examined the gills, skin, and anal vents of yellowfin (n= 3), skipjack (n= 1), and albacore (n= 6) tuna for the presence of indigenous HPB. Thirteen HPB strains were isolated from the anal vent samples from albacore (n= 3) and yellowfin (n= 2) tuna. Four of these isolates were identified asPhotobacterium kishitaniiand nine isolates asPhotobacterium angustum; these isolates produced 560 to 603 and 1,582 to 2,338 ppm histamine in marine broth containing 1% histidine (25°C for 48 h), respectively. The optimum growth temperatures and salt concentrations were 26 to 27°C and 1% salt forP. kishitaniiand 30 to 32°C and 2% salt forP. angustumin Luria 70% seawater (LSW-70). The optimum activity of the HDC enzyme was at 15 to 30°C for both species. At 5°C,P. kishitaniiandP. angustumhad growth rates of 0.1 and 0.2 h−1, respectively, and the activities of histidine decarboxylase (HDC) enzymes were 71% and 63%, respectively. These results show that indigenous HPB in tuna are capable of growing at elevated and refrigeration temperatures. These findings demonstrate the need to examine the relationships between the rate of histamine production at refrigeration temperatures, seafood shelf life, and regulatory limits.

ABSTRACT There is current interest in biological sources of acetone, a volatile organic compound that impacts atmospheric chemistry. Here, we determined that leucine-dependent acetone formation is widespread in the Vibrionaceae. Sixteen Vibrio isolates, twoListonella species, and two Photobacterium angustum isolates produced acetone in the presence ofl-leucine. Shewanella isolates produced much less acetone. Growth of Vibrio splendidus and P. angustum in a fermentor with controlled aeration revealed that acetone was produced after a lag in late logarithmic or stationary phase of growth, depending on the medium, and was not derived from acetoacetate by nonenzymatic decarboxylation in the medium.l-Leucine, but not d-leucine, was converted to acetone with a stoichiometry of approximately 0.61 mol of acetone per mol of l-leucine. Testing various potential leucine catabolites as precursors of acetone showed that only α-ketoisocaproate was efficiently converted by whole cells to acetone. Acetone production was blocked by a nitrogen atmosphere but not by electron transport inhibitors, suggesting that an oxygen-dependent reaction is required for leucine catabolism. Metabolic labeling with deuterated (isopropyl-d7)-l-leucine revealed that the isopropyl carbons give rise to acetone with full retention of deuterium in each methyl group. These results suggest the operation of a new catabolic pathway for leucine in vibrios that is distinct from the 3-hydroxy-3-methylglutaryl-coenzyme A pathway seen in pseudomonads.

ABSTRACT Iron (Fe) limitation is known to affect heterotrophic bacteria within the respiratory electron transport chain, therefore strongly impacting the overall intracellular energy production. We investigated whether the gene expression pattern of the light-sensitive proton pump, proteorhodopsin (PR), is influenced by varying light, carbon and Fe concentrations in the marine bacterium Photobacterium angustum S14 and whether PR can alleviate the physiological processes associated with Fe starvation. Our results show that the gene expression of PR increases as cells enter the stationary phase, irrespective of Fe-replete or Fe-limiting conditions. This upregulation is coupled to a reduction in cell size, indicating that PR gene regulation is associated with a specific starvation-stress response. We provide experimental evidence that PR gene expression does not result in an increased growth rate, cell abundance, enhanced survival or ATP concentration within the cell in either Fe-replete or Fe-limiting conditions. However, independent of PR gene expression, the presence of light did influence bacterial growth rates and maximum cell abundances under varying Fe regimes. Our observations support previous results indicating that PR phototrophy seems to play an important role within the stationary phase for several members of the Vibrionaceae family, but that the exact role of PR in Fe limitation remains to be further explored.

Depuis sa découverte, les études concernant la protéorhodopsine sont de plus en plus nombreuses. L’hypothèse qu’elle apporte des avantages dans des conditions pauvres en nutriments aux procaryotes contenant la protéorhodopsine par rapport aux hétérotrophes stricts a été explorée à plusieurs reprises et paraît être la plus probable. Dans ces travaux de thèse, nous contribuons à augmenter les connaissances son rôle dans l’efficacité d’utilisation du carbone organique disponible en utilisant une Gammaprotéobactérie contenant la protéorhodopsine en présence et en absence de lumière. La culture continue a été utilisée afin de s’approcher au mieux des conditions environnementales. Les rendements et la maintenance énergétique ont été déterminés en suivant le modèle de Pirt (1965) dans des conditions de pH acide ou sans stress par le pH. Ce travail a permis de montrer que la maintenance énergétique à l’obscurité était beaucoup plus élevée dans les conditions de stress. Cependant, lorsque la population bactérienne était exposée en cycle lumière-obscurité, l’énergie nécessaire à son maintien était significativement diminuée tout au long du cycle. Bien que le rendement soit plus important avec un pH plus optimal, l’exposition en cycle lumière-obscurité n’apportait pas les avantages observés dans les conditions de stress par le pH. Donc, il semblerait que la réponse à la lumière de P. Angustum S14 soit plus liée à la balance énergétique qu’à la concentration de substrat. Ces résultats innovants ont permis de soulever une hypothèse quant aux raisons pour lesquelles de nombreuses études n’ont pas vu d’effet positif de la lumière sur la croissance et le rendement des souches étudiées
Since its discovery more than 10 years ago, there are more and more studies about proteorhodopsin. This protein seems to be significant in marine ecology considering its large global distribution among many bacterial taxa; but its role remains controversial. Although light response from proteorhodopsin-containing prokaryotes (PCPs) seems to be strain-dependent, it has been hypothesized that the main function of proteorhodopsin was to provide an advantage to PCPs during starvation conditions. In this work, we investigated the increase knowledge about the role of proteorhodopsin regarding the organic carbon utilization efficiency measured in the proteorhodopsin-containing Gammaproteobacterium (Photobacterium angustum S14) in the light compared to the dark. Carbon-limited continuous cultures have been used to mimic environmental conditions. Yields and energetic maintenance were determined according to Pirt’s model (1965) with acid pH or without supplementary pH-stress. We observed highest energetic maintenance in the dark under pH stress condition. However, when light-dark cycles were used, the energy required for bacterial maintenance was significantly decreased during all the run and nearly in the range without pH stress. Taking together, it seems that the response of P. Angustum S14 to light is more linked to the energetic balance than substrate concentration. The innovative results indicate a possible reason why many studies did not observe positive effects on bacterial growth and yield. In addition, PCP sequencing was performed to confirm these conclusions at a more large taxa scale

Le fer (Fe) est un élément essentiel de la croissance microbienne marine, mais est présent sous forme de trace dans les eaux de surface des océans. Chez les bactéries hétérotrophes, la limitation en Fe affecte particulièrement la production d'ATP et il a été démontré que les bactéries appliquent diverses stratégies pour faire face à la présence de limitation en Fe. Les outils génétiques nous ont permis de tester deux stratégies potentielles au sein de l'organisme modèle Photobacterium angustum S14. Le shunt glyoxylique, une voie métabolique trouvée dans les bactéries aérobies contournant plusieurs étapes de TCA, s’est révélée être régulée à la hausse sous une limitation en Fe et nous proposons que la dérivation du shunt glyoxylique réoriente le métabolisme cellulaire de la chaîne de transport d’électrons, augmentant de ce fait l'efficacité métabolique de la cellule soumise à la limitation en Fe. La protéorhodopsine, une pompe à protons activée par la lumière trouvée dans plusieurs bactéries hétérotrophes, peut atténuer le stress lié au Fe si le gradient de proton produit est couplé à l'ATP synthase. Nos résultats ont montré que la protéorhodopsine augmentait à mesure que les cellules approchaient de la phase stationnaire dans des conditions à la fois remplies de Fe et limitant en Fe, mais étaient absentes pendant la phase exponentielle. Les travaux futurs visant à élucider le rôle de la protéorhodopsine, et en particulier en ce qui concerne la limitation du Fe, devraient donc être axés sur la phase stationnaire d'une cellule bactérienne. Les résultats de ce manuscrit de thèse ont contribué à la littérature actuelle sur la polyvalence des bactéries marines hétérotrophes pour faire face à la limitation en Fe et le rôle de la protéorhodopsine et du shunt glyoxylique dans l'environnement marin
Iron (Fe) is an essential element for marine microbial growth but is present in trace amounts in the surface waters of the ocean. In heterotrophic bacteria, Fe-limitation particularly impacts ATP production and have been shown to implement various strategies to cope in the presence of Fe-limitation. Genetic tools enabled us to test two potential strategies within the model organism Photobacterium angustum S14. The glyoxylate shunt, a metabolic pathway found in aerobic bacteria bypassing several steps within the classic tricarboxylic acid (TCA) was shown to be upregulated under Fe-limitation and we propose that the glyoxylate shunt was able to redirect a cell’s metabolism away from Fe-limiting steps within the electron transport, thereby increasing the metabolic efficiency of the cell under Fe-limitation. Proteorhodopsin, a light activated proton pump found in several heterotrophic bacteria, could alleviate Fe-stress if the produced proton gradient is coupled to ATP synthase. Our results showed that proteorhodopsin is upregulated as cells approached the stationary phase under both Fe-replete and Fe-limiting conditions but was absent during the exponential phase. Future work in elucidating the role of proteorhodopsin, and particularly under Fe-limitation, should therefore focus on the stationary phase of a bacterial cell. The results from this thesis manuscript contributed to a culminating body of work surrounding the versatility of marine heterotrophic bacteria in coping with Fe-limitation and is an appropriate addition to the literature surrounding the role of proteorhodopsin and the glyoxylate shunt within the marine environment