Azospirillum brasilense Cd was grown in ammonium–malate mineral salts medium in batch culture and in chemostat continuous culture. It was found that poly-β-hydroxybutyrate synthesis was favored under oxygen limitation in chemostat culture and under high C/N ratios towards the end of exponential growth in batch culture. The degradation and synthesis of poly-β-hydroxybutyrate under starvation conditions occurred in a biphasic pattern and was affected by the poly-β-hydroxybutyrate content of the cells. During a 7-day incubation period in phosphate buffer, the survival and respiration rate of bacteria containing about 40% poly-β-hydroxybutyrate (dry weight) were higher than those of cells containing about 5% poly-β-hydroxybutyrate. Polymer-rich cells fixed atmospheric nitrogen in the absence of exogenous carbon and combined nitrogen. Biphasic nitrogenase activity was observed during starvation. When nitrogenase activity was high, hydroxybutyrate dehydrogenase activity was low and vice versa. Aerotactic response was higher in polymer-rich cells. In the presence of stress factors such as ultraviolet irradiation, dessication, and osmotic pressure poly-β-hydroxybutyrate-poor cells died more rapidly than poly-β-hydroxybutyrate-rich cells.

Tilapia lake virus disease (TiLVD) has emerged to be an important viral disease of farmed Nile tilapia (Oreochromis niloticus) having the potential to impede expansion of aquaculture production. There is a need for rapid diagnostic tools to identify infected fish to limit the spread in individual farms. We report the first detection of TiLV infection by PCR in farmed and wild Nile tilapia from Lake Victoria. There was no difference in prevalence between farmed and wild fish samples (p = .65), and of the 442 samples examined from 191 fish, 28 were positive for TiLV by PCR. In terms of tissue distribution, the head kidney (7.69%, N = 65) and spleen (10.99%, N = 191), samples had the highest prevalence (p < .0028) followed by heart samples (3.45%, N = 29). Conversely, the prevalence was low in the liver (0.71%, N = 140) and absent in brain samples (0.0%, N = 17), which have previously been shown to be target organs during acute infections. Phylogenetic analysis showed homology between our sequences and those from recent outbreaks in Israel and Thailand. Given that these findings were based on nucleic acid detection by PCR, future studies should seek to isolate the virus from fish in Lake Victoria and show its ability to cause disease and virulence in susceptible fish.

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With the rapid global spread of West Nile virus (WNV) and the endemic state it has acquired in new geographical areas, we hereby bring a thorough serological investigation of WNV in horses in a longstanding endemic region, such as Israel. This study evaluates the environmental and demographic risk factors for WNV infection in horses and suggests possible factors associated with the transition from endemic to epidemic state. West Nile virus seroprevalence in horses in Israel was determined throughout a period of more than a decade, before (1997) and after (2002 and 2013) the massive West Nile fever outbreak in humans and horses in 2000. An increase in seroprevalence was observed, from 39% (113/290) in 1997 to 66.1% (547/827) in 2002 and 85.5% (153/179) in 2013, with persistent significantly higher seroprevalence in horses situated along the Great Rift Valley (GRV) area, the major birds' migration route in Israel. Demographic risk factors included age and breed of the horse. Significantly lower spring precipitation was observed during years with increased human incidence rate that occurred between 1997–2007. Hence, we suggest referring to Israel as two WNV distinct epidemiological regions; an endemic region along the birds' migration route (GRV) and the rest of the country which perhaps suffers from cyclic epidemics. In addition, weather conditions, such as periods of spring drought, might be associated with the transition from endemic state to epidemic state of WNV.

Activities of the enzymes which are involved in the poly-P-hydroxybutyrate (PHB) cycle, in both synthesis and degradation reactions, were assayed in crude extracts of Azospirilum brasilense cells containing different amounts of PHB. The enzymes of the PHB cycle, of both the synthesis and the degradation process, were more active in PHB-rich cells than in PHB-poor cells. During 96 h of starvation of cells suspended in phosphate buffer, enzymes of the PHB cycle were more active in PHB-rich cells. There was a peak of activity of hydroxybutyrate dehydrogenase (BOHB-DH), P-ketothiolase and thiophorase after 24 h of starvation, due to polymer degradation. During the following hours of starvation there was a decrease in the activity of these enzymes. After 24 h of starvation the activity of acetoacetyl-CoA reductase dropped to a minimum level, because the cells could not synthesize PHB under these conditions. The specific activities of BOHB-DH, P-ketothiolase and thiophorase were higher in A. brasiZense cells which were grown under low oxygen tension and consequently accumulated high levels of PHB, than in cells grown under high oxygen tension, with a low PHB content. Similarities to the pathway of PHB biosynthesis and degradation and its control in Azofobacfer beijevnckii are described.

No abstract

Tilapia is the second most farmed fish species after carp in the world. However, the production has come under threat due to emerging diseases such as tilapia lake virus (TiLV) that causes massive mortalities with high economic losses. It is largely unknown whether different tilapia strains are equally susceptible to TiLV infection. In the present study we compared the susceptibility of gray (Oreochromis niloticus x O. aureus) and red tilapia (Oreochromis spp.) to experimental TiLV infection. Virus was injected intraperitoneally at a concentration of 104 TCID50/mL. Our findings show that gray tilapia had a lower mortality, 86.44%, but statistically not significantly different (p = 0.068) from red tilapia (100%). The duration of the mortality period from onset to cessation was similar for the two species, starting at 2–3 days post challenge (dpc) with a median at 10–11 dpi and ending on 20–22 dpi. In addition, there was no difference between species in mean viral loads in brain, liver and headkidney from fish collected soon after death. As for host response, expression levels of IL-1β and TNFα were equally high in brain and headkidney samples while levels in liver samples were low for both red and gray tilapia, which coincides with lower viral loads in liver compared to brain and headkidney for both species. We find that red and gray tilapia were equally susceptible to TiLV infection with similar post challenge mortality levels, equal virus concentration in target organs and similar proinflammatory cytokine responses in target and lymphoid organs at time of death. Nonetheless, we advocate that the search for less susceptible tilapia strains should continue with the view to reduce losses from TiLV infection in aquaculture.

D ( -)-0-hydroxybutyrate dehydrogenase (BOHB-DH) (EC 1.1.1.30) was puri6ed 991-fold from Azospidlum brasilense Cd. Its specific activity was 5650 units (mg protein)-l min-'. The enzyme is a tetramer, with identical subunits and a total molecular mass of 100 kDa. BOHB-DH is not a glycoprotein. It is acidic and contains six disulphide bonds without free S H groups. Under the assay conditions used, BOHB-DH activity was maximal at pH 8.0 and at 36 OC. The enzyme is an NAD+ oxidoreductase, and is inhibited by NADPH and NADH. It has high affinity for P-hydroxybutyrate: the K, value for the P-hydroxybutyrate substrate is 1 mM. Adenosine phosphates, pyruvate, acetyl-coenzyme A, oxaloacetate and 2-oxoglutarate inhibited purified BOHB-DH.