A Novel Soybean Diacylglycerol Acyltransferase 1b Variant with Three Amino Acid Substitutions Increases Seed Oil Content

Improving soybean (Glycine max) seed composition by increasing the protein and oil components will add significant value to the crop and enhance environmental sustainability. Diacylglycerol acyltransferase (DGAT) catalyzes the final rate-limiting step in triacylglycerol (TAG) biosynthesis and has a major impact on seed oil accumulation. We previously identified a soybean DGAT1b variant with 14 amino acid substitutions (GmDGAT1b-MOD) that increases total oil content by 3 percentage points when overexpressed in soybean seeds. In the present study, additional GmDGAT1b variants were generated to further increase oil with a reduced number of substitutions. Variants with one to four amino acid substitutions were screened in the model systems S. cerevisiae and transient N. benthamiana leaf. Promising GmDGAT1b variants resulting in high oil accumulation in the model systems were selected for over-expression in soybeans. One GmDGAT1b variant with three novel amino acid substitutions (GmDGAT1b-3aa) increased total soybean oil to levels near the previously discovered GmDGAT1b-MOD variant. In a multiple location field trial, GmDGAT1b-3aa transgenic events had significantly increased oil and protein by up to 2.3 and 0.6 percentage points, respectively. Modeling of the GmDGAT1b-3aa protein structure provided insights into the potential function of the three substitutions. These findings will guide efforts to improve soybean oil content and overall seed composition by CRISPR editing.

RNAi and CRISPR-Cas silencing E3-RING ubiquitin ligase AIP2 enhances soybean seed protein content

The majority of plant protein in the world's food supply is derived from soybean (Glycine max). Soybean is a key protein source for global animal feed and is incorporated into plant-based foods for people, including meat alternatives. Soybean protein content is genetically variable and is usually inversely related to seed oil content. ABI3-interacting protein 2 (AIP2) is an E3-RING ubiquitin ligase that targets the seed-specific transcription factor ABI3. Silencing both soybean AIP2 genes (AIP2a and AIP2b) by RNAi enhanced seed protein content by up to seven percentage points, with no significant decrease in seed oil content. The protein content enhancement did not alter the composition of the seed storage proteins. Inactivation of either AIP2a or AIP2b by a CRISPR-Cas9-mediated mutation increased seed protein content, and this effect was greater when both genes were inactivated. Transactivation assays in transfected soybean hypocotyl protoplasts indicated that ABI3 changes the expression of glycinin, conglycinin, 2S albumin, and oleosin genes, indicating that AIP2 depletion increased seed protein content by regulating activity of the ABI3 transcription factor protein. These results provide an example of a gene-editing prototype directed to improve global food security and protein availability in soybean that may also be applicable to other protein-source crops.

Loss-of-function of triacylglycerol lipases are associated with low flour rancidity in pearl millet [Pennisetum glaucum (L.) R. Br.]

Pearl millet is an important cereal crop of semi-arid regions since it is highly nutritious and climate resilient. However, pearl millet is underutilized commercially due to the rapid onset of hydrolytic rancidity of seed lipids post-milling. We investigated the underlying biochemical and molecular mechanisms of rancidity development in the flour from contrasting inbred lines under accelerated aging conditions. The breakdown of storage lipids (triacylglycerols; TAG) was accompanied by free fatty acid accumulation over the time course for all lines. The high rancidity lines had the highest amount of FFA by day 21, suggesting that TAG lipases may be the cause of rancidity. Additionally, the high rancidity lines manifested substantial amounts of volatile aldehyde compounds, which are characteristic products of lipid oxidation. Lipases with expression in seed post-milling were sequenced from low and high rancidity lines. Polymorphisms were identified in two TAG lipase genes (PgTAGLip1 and PgTAGLip2) from the low rancidity line. Expression in a yeast model system confirmed these mutants were non-functional. We provide a direct mechanism to alleviate rancidity in pearl millet flour by identifying mutations in key TAG lipase genes that are associated with low rancidity. These genetic variations can be exploited through molecular breeding or precision genome technologies to develop elite pearl millet cultivars with improved flour shelf life.

An Improved Variant of Soybean Type 1 Diacylglycerol Acyltransferase Increases the Oil Content and Decreases the Soluble Carbohydrate Content of Soybeans

Kinetically improved diacylglycerol acyltransferase (DGAT) variants were created to favorably alter carbon partitioning in soybean (Glycine max) seeds. Initially, variants of a type 1 DGAT from a high-oil, high-oleic acid plant seed, Corylus americana, were screened for high oil content in Saccharomyces cerevisiae Nearly all DGAT variants examined from high-oil strains had increased affinity for oleoyl-CoA, with S0.5 values decreased as much as 4.7-fold compared with the wild-type value of 0.94 µm Improved soybean DGAT variants were then designed to include amino acid substitutions observed in promising C. americana DGAT variants. The expression of soybean and C. americana DGAT variants in soybean somatic embryos resulted in oil contents as high as 10% and 12%, respectively, compared with only 5% and 7.6% oil achieved by overexpressing the corresponding wild-type DGATs. The affinity for oleoyl-CoA correlated strongly with oil content. The soybean DGAT variant that gave the greatest oil increase contained 14 amino acid substitutions out of a total of 504 (97% sequence identity with native). Seed-preferred expression of this soybean DGAT1 variant increased oil content of soybean seeds by an average of 3% (16% relative increase) in highly replicated, single-location field trials. The DGAT transgenes significantly reduced the soluble carbohydrate content of mature seeds and increased the seed protein content of some events. This study demonstrated that engineering of the native DGAT enzyme is an effective strategy to improve the oil content and value of soybeans.

Studies on the regulation of lipid biosynthesis in plants: application of control analysis to soybean

Although there is much knowledge of the enzymology (and genes coding the proteins) of lipid biosynthesis in higher plants, relatively little attention has been paid to regulation. We have demonstrated the important role for cholinephosphate cytidylyltransferase in the biosynthesis of the major extra-plastidic membrane lipid, phosphatidylcholine. We followed this work by applying control analysis to light-induced fatty acid synthesis. This was the first such application to lipid synthesis in any organism. The data showed that acetyl-CoA carboxylase was very important, exerting about half of the total control. We then applied metabolic control analysis to lipid accumulation in important oil crops - oilpalm, olive, and rapeseed. Recent data with soybean show that the block of fatty acid biosynthesis reactions exerts somewhat more control (63%) than lipid assembly although both are clearly very important. These results suggest that gene stacks, targeting both parts of the overall lipid synthesis pathway will be needed to increase significantly oil yields in soybean. This article is part of a Special Issue entitled: Membrane Structure and Function: Relevance in the Cell's Physiology, Pathology and Therapy.

Influence of carbon to nitrogen ratios on soybean somatic embryo (cv. Jack) growth and composition

Soybean [Glycine max (L.) Merr.] seed are valued for their protein and oil content. Soybean somatic embryos cultured in Soybean Histodifferentiation and Maturation (SHaM) medium were examined for their suitability as a model system for developing an understanding of assimilate partitioning and metabolic control points for protein and oil biosynthesis in soybean seed. This report describes the growth dynamics and compositional changes of SHaM embryos in response to change in the carbon to nitrogen ratio of the medium. It was postulated that at media compositions that were sufficient to support maximal growth rates, changes in the C:N ratio are likely to influence the partitioning of resources between the various storage products, especially protein and oil. As postulated, at steady-state growth rates, embryo protein content was strongly correlated with decreasing C:N ratios and increasing glutamine consumption rates. However, oil content remained relatively unchanged across the C:N ratio range tested, and resources were instead directed towards the starch and residual biomass (estimated by mass balance) pools in response to increasing C:N ratios. Protein and oil were inversely related only at concentrations of sucrose in the medium <88 mM, where carbon limited growth and no starch was found to accumulate in the tissues. These observations and the high reproducibility in the data indicate that SHaM embryos are an ideal model system for the application of metabolic flux analysis studies designed to test hypotheses regarding assimilate partitioning in developing soybean seeds.

Oil and protein accumulation in developing seeds is influenced by the expression of a cytosolic pyrophosphatase in Arabidopsis

This study describes a dominant low-seed-oil mutant (lo15571) of Arabidopsis (Arabidopsis thaliana) generated by enhancer tagging. Compositional analysis of developing siliques and mature seeds indicated reduced conversion of photoassimilates to oil. Immunoblot analysis revealed increased levels of At1g01050 protein in developing siliques of lo15571. At1g01050 encodes a soluble, cytosolic pyrophosphatase and is one of five closely related genes that share predicted cytosolic localization and at least 70% amino acid sequence identity. Expression of At1g01050 using a seed-preferred promoter recreated most features of the lo15571 seed phenotype, including low seed oil content and increased levels of transient starch and soluble sugars in developing siliques. Seed-preferred RNA interference-mediated silencing of At1g01050 and At3g53620, a second cytosolic pyrophosphatase gene that shows expression during seed filling, led to a heritable oil increase of 1% to 4%, mostly at the expense of seed storage protein. These results are consistent with a scenario in which the rate of mobilization of sucrose, for precursor supply of seed storage lipid biosynthesis by cytosolic glycolysis, is strongly influenced by the expression of endogenous pyrophosphatase enzymes. This emphasizes the central role of pyrophosphate-dependent reactions supporting cytosolic glycolysis during seed maturation when ATP supply is low, presumably due to hypoxic conditions. This route is the major route providing precursors for seed oil biosynthesis. ATP-dependent reactions at the entry point of glycolysis in the cytosol or plastid cannot fully compensate for the loss of oil content observed in transgenic events with increased expression of cytosolic pyrophosphatase enzyme in the cytosol. These findings shed new light on the dynamic properties of cytosolic pyrophosphate pools in developing seed and their influence on carbon partitioning during seed filling. Finally, our work uniquely demonstrates that genes encoding cytosolic pyrophosphatase enzymes provide novel targets to improve seed composition for plant biotechnology applications.

Overexpression of the Arabidopsis CBF3 transcriptional activator mimics multiple biochemical changes associated with cold acclimation

We further investigated the role of the Arabidopsis CBF regulatory genes in cold acclimation, the process whereby certain plants increase in freezing tolerance upon exposure to low temperature. The CBF genes, which are rapidly induced in response to low temperature, encode transcriptional activators that control the expression of genes containing the C-repeat/dehydration responsive element DNA regulatory element in their promoters. Constitutive expression of either CBF1 or CBF3 (also known as DREB1b and DREB1a, respectively) in transgenic Arabidopsis plants has been shown to induce the expression of target COR (cold-regulated) genes and to enhance freezing tolerance in nonacclimated plants. Here we demonstrate that overexpression of CBF3 in Arabidopsis also increases the freezing tolerance of cold-acclimated plants. Moreover, we show that it results in multiple biochemical changes associated with cold acclimation: CBF3-expressing plants had elevated levels of proline (Pro) and total soluble sugars, including sucrose, raffinose, glucose, and fructose. Plants overexpressing CBF3 also had elevated P5CS transcript levels suggesting that the increase in Pro levels resulted, at least in part, from increased expression of the key Pro biosynthetic enzyme Delta(1)-pyrroline-5-carboxylate synthase. These results lead us to propose that CBF3 integrates the activation of multiple components of the cold acclimation response.

Molecular cloning of mannose-6-phosphate reductase and its developmental expression in celery

Compared with other primary photosynthetic products (e.g. sucrose and starch), little is known about sugar alcohol metabolism, its regulation, and the manner in which it is integrated with other pathways. Mannose-6-phosphate reductase (M6PR) is a key enzyme that is involved in mannitol biosynthesis in celery (Apium graveolens L.). The M6PR gene was cloned from a leaf cDNA library, and clonal authenticity was established by assays of M6PR activity, western blots, and comparisons of the deduced amino acid sequence with a celery M6PR tryptic digestion product. Recombinant M6PR, purified from Escherichia coli, had specific activity, molecular mass, and kinetic characteristics indistinguishable from those of authentic celery M6PR. Sequence analyses showed M6PR to be a member of the aldo-keto reductase superfamily, which includes both animal and plant enzymes. The greatest sequence similarity was with aldose-6-phosphate reductase (EC 1.1.1.200), a key enzyme in sorbitol synthesis in Rosaceae. Developmental studies showed M6PR to be limited to green tissues and to be under tight transcriptional regulation during leaf initiation, expansion, and maturation. These data confirmed a close relationship between the development of photosynthetic capacity, mannitol synthesis, and M6PR activity.

A twelve-year study of leptospirosis on Barbados

Between November 1979 and December 1991, 398 cases of severe leptospirosis were confirmed on Barbados (range for 1980-1991 23-56; mean 32.7; incidence 13.3/100,000/year). For the six-year periods 1980-1985 and 1986-1991 there was no significant change in incidence with time. Incidence is unlikely to change significantly in the next decade. Monthly average case numbers ranged from 1.4 (July) to 4.3 (November). The average (2.8) for June to December (the 7 wetter months) was not significantly higher than that (2.5) for January to May (the 5 drier months). The age range was 7-86. There were three times as many male cases (302) as female (96), and nearly 10 times as many in those < 35. Although the highest number of cases (69) was in males aged 15-24, the highest incidence was in the older age groups, particularly the male 65-74 year-olds, and the female 55-64 year-olds. Leptospirosis was the proven cause of death in 55 (13.8%) hospital patients (annual range 0-13, mean 4.5). Some of a further 39 fatalities might have been cases. Death from leptospirosis was nearly twice as common among the women as among the men. Only one patient under 20 years of age died. Leptospira were isolated and identified from 117 (29.4%) of the 398 sick patients. The infecting organisms were bim (serogroup Autumnalis--75), copenhageni (Icterohaemorrhagiae-26), arborea (Ballum-14) and bajan (Australis-2). These infecting serovars could not be distinguished clinically, but infection was milder in children than in adults. Despite its predominance in surveyed children, serogroup Panama was virtually absent in this study. Rainfall is the major factor affecting the distribution of cases; not surprisingly, sanitation workers and agricultural workers appear to be the groups at highest risk. The general lack of clear-cut risk factors reflects the ubiquity of leptospires in the environment and the fact that the disease is not entirely occupational.

Mongoose rabies in the Caribbean

Mongooses (Herpestes auropunctatus) have been introduced into most of the larger Caribbean islands, some notable exceptions being Dominica, Tobago, and Montserrat. Rabies in Caribbean mongooses is present in Puerto Rico, Cuba, the Dominican Republic (and presumably Haiti), and Grenada. Bat rabies is known on Cuba, Grenada, and Trinidad, although mongooses found on Trinidad are free of the disease. None of the other islands is known to have rabies, although it could be present in sequestered bat populations. All reported case numbers of mongoose rabies in the Caribbean are underestimates, and available information is at best incomplete and at times fragmentary. Nevertheless, data are presented from the four affected islands. Mongoose reduction campaigns have been undertaken on Cuba and Grenada. In Cuba strychnine sulfate inoculated into labeled eggs is used, whereas in Grenada sodium fluoroacetate (1080) has been used in boiled cowhide baits. Mongoose poisoning is unsatisfactory and ineffective in the long-term. Because many mongooses naturally exposed to rabies virus develop serum neutralizing antibodies and are considered to be immunized, possibly for life, vaccination in the wild has been under consideration since the mid-1970s. Early attempts to produce a pill coated with ERA vaccine for enteric absorption in mongooses were not very successful, but new modified vaccines and recombinant techniques hold considerable promise.

Production of polyclonal antibodies in rabbits is simplified using perforated plastic golf balls

Production of polyclonal antibodies in the lumen of a perforated golf ball implanted surgically under the skin of a rabbit offers advantages over conventional techniques. Less stress is placed on the rabbit because bleeding is eliminated, complete adjuvants are not used and animal handling is minimized. The technique also offers the advantage that large amounts of antibody-containing fluid can be removed easily from the ball. In this report we describe the surgical protocol and demonstrate use of this technique to produce high-titered antibodies to plant and plant viral proteins.

Mannitol Synthesis in Higher Plants : Evidence for the Role and Characterization of a NADPH-Dependent Mannose 6-Phosphate Reductase

Mannitol is a major photosynthetic product in many algae and higher plants. Photosynthetic pulse and pulse-chase (14)C-radiolabeling studies with the mannitol-synthesizing species, celery (Apium graveolens L.) and privet (Ligustrum vulgare L.), showed that mannose 6-phosphate (M6P) and mannitol 1-phosphate were among the early photosynthetic products. A NADPH-dependent M6P reductase was detected in these species (representing two different higher plant families), and the enzyme was purified to apparent homogeneity (68-fold with a 22% yield) and characterized from celery leaf extracts. The celery enzyme had a monomeric molecular mass, estimated from mobilities on sodium dodecyl sulfate-polyacrylamide gels, of 35 kilodaltons. The isoelectric point was pH 4.9; the apparent K(m) (M6P) was 15.8 millimolar, but the apparent K(m) (mannitol 1-phosphate) averaged threefold higher; pH optima were 7.5 with M6P/NADPH and 8.5 with mannitol 1-phosphate/NADP as substrates. Substrate and cofactor requirements were quite specific. NADH did not substitute for NADPH, and there was no detectable activity with fructose 6-phosphate, glucose 6-phosphate, fructose 1-phosphate, mannose 1-phosphate, mannose, or mannitol. NAD only partially substituted for NADP. Mg(2+), Ca(2+), Zn(2+), and fructose-2,6-bisphosphate had no apparent effects on the purified enzyme's activity. In vivo radiolabeling results and the enzyme's kinetics, specificity, and distribution (in two-plant families) all suggest that NADPH-dependent M6P reductase plays an important role in mannitol biosynthesis in higher plants.

An investigation of some risk factors for severe leptospirosis on Barbados

Between November 1979 and the end of December 1986 (7.17 years), 248 cases of leptospirosis were confirmed among hospital patients on Barbados (mean 35 per year; range 25-57). Considering the 235 who were greater than or equal to 15 years of age, the annual incidence of leptospirosis was 19.2/100,000 population (14.0 for all age groups). There were 173 males and 62 females, and for cases aged 15-34 leptospirosis was 9.6 times more common in men than women. Among men, incidence increased fairly steadily with age, and an even steadier increase was apparent in women up to age 64, with some decline in later years. The incidence of disease was much higher among agricultural than other workers and the non-employed. Highest case numbers were recorded in the parishes of St Michael (65 or 28%) and Christ Church (36 or 15%), though the incidence was lowest in these two parishes (13.1/100,000 and 17.4/100,000, respectively). The highest incidence rates were in St Andrew and St Joseph (50.2 and 36.1/100,000, respectively). The incidence in areas with rainfall greater than or equal to 1600 mm (32.6/100,000) was nearly twice that in areas with rainfall less than 1600 mm (17.3/100,000). There is a clear link between cases of severe disease and recent rainfall. Using 134 patients greater than or equal to 15 years of age with fever due to other illnesses as controls, a higher proportion of cases than controls came from rural areas. The risk of contracting leptospirosis was increased for all categories of manual workers relative to the group at lowest risk (non-manual indoor workers). Sugar-cane workers were five times more likely to contract leptospirosis than were non-manual indoor workers, while those whose families minded livestock were 2.5 times more likely, and those with rodents in their garden/yard were 1.8 times more likely to do so. Other risk factors examined did not show significant associations with the disease. Despite increasing mechanization and the use of more protective clothing, agricultural workers are still at high risk from leptospirosis. The annual range of cases is likely to stay much as it is in the foreseeable future.

Leptospires in Rattus spp. on Barbados

Among 138 Rattus norvegicus and 98 R. rattus trapped on Barbados in 1964-65 and examined for evidence of leptospiral infection, seropositivity prevalence rates were similar (34 and 30%, respectively), but isolation/dark field microscopy rates were higher in R. norvegicus (27%) than R. rattus (15%). R. norvegicus carried mainly serogroup Icterohaemorrhagiae and R. rattus mainly serogroup Autumnalis. These two serogroups cause 90% of severe human leptospirosis on the island.

Leptospiral antibodies in patients from a Barbadian general practice

Sera from 1,419 patients who attended a Barbadian general practice for a variety of complaints between 1 April 1984 and 30 April 1988 were examined for leptospiral agglutinins by the microscopic agglutination test (MAT). Sera from the 42 patients with pyrexia of unknown origin, jaundice or kidney involvement, and the 26 patients with titres greater than or equal to 1:400 in the MAT, were also examined by the ELISA for IgM and IgG antibodies. Current or recent mild leptospiral infection was diagnosed in four of the patients, but some mild cases may have been missed. Two further cases of leptospirosis were recorded after the study period ended; both were very ill but responded well to doxycycline therapy. Altogether 177 of the 1,419 patients (12.5%) had agglutination titres greater than or equal to 1:50. These were 104/739 males (14%) and 73/680 females (11%). Seropositivity tended to increase with age (p less than 0.01), and the highest rates were in agricultural workers (35%), labourers (24%) and non-manual outdoor workers (19%). The difference in seropositivity between the main occupational groups was highly significant (p less than 0.001). The serogroups most commonly recorded among the seropositive patients were Autumnalis (31%), Panama (26%), Australis (24%) and Pyrogenes (20%). Autumnalis predominated in each of the main occupational groups except indoor non-manual workers where Panama, Pyrogenes and Australis occurred more frequently. 95% of the positive titres ranged between 1:50 and 1:400. Titres tended to increase with age, but there was no obvious association between higher titres and particular occupations.(ABSTRACT TRUNCATED AT 250 WORDS)

Leptospires in the whistling frog (Eleutherodactylus johnstonei) on Barbados

Two groups of whistling frogs (Eleutherodactylus johnstonei) comprising 99 and 117 animals were examined for leptospiral infection. Group I animals were caught in 14 areas of Barbados, and Group II animals in seven areas of suburban Bridgetown. Leptospires were isolated from the kidneys or body fluid of six frogs in Group I and the kidneys of 3 frogs in Group II. Two of the Group I isolates died out; the others were identified as bajan (a new serovar in the Australis serogroup) (6) and bim (Autumnalis) (1). The macerated body tissues and fluid of Group I frogs were put into phosphate buffered saline and examined by the microscopic agglutination test using 22 antigens. The results were all negative. For the Group II frogs the methodology was altered; blood was collected onto filter paper discs and allowed to dry out before being agitated in PBS and examined by the MAT. 15/117 (12.8%) animals were positive at greater than or equal to 1:100 and 19 (16.2%) at greater than or equal to 1:50. The geometric mean titre was 179. Seventeen of the sera reacted predominantly to antigens in the Australis serogroup, and two to Pyrogenes on its own. The serological results reflected the identity of the isolates. Serovars of Australis are not known to cause illness on Barbados, but bim is the commonest cause of severe leptospirosis on the island.

Mongoose rabies

Mongooses are indigenous to Africa and Asia and have been introduced elsewhere. In Cuba, Puerto Rico, Grenada, and South Africa they are the major reservoir and vector of rabies. Elsewhere, sporadic cases of mongoose rabies are reported, but dog rabies can mask their importance. Population density probably determines the importance of the mongoose as a reservoir of rabies. In Grenada during a 4-year period, nearly 30% (and in some areas greater than 50%) of mongooses were found to have rabies serum neutralizing antibodies. The annual proportions of mongooses that were serum antibody-positive and virus-positive, respectively, were inversely related. Natural immunity in mongooses probably lasts for life. In contrast with foxes, in mongooses immunity is an important factor in the epizootiology of rabies. Inoculation of mongooses with Evelyn-Rokitnicki-Abelseth (ERA) vaccine induced a good immunologic response and augurs well for the success of vaccination in the field. The effects of wildlife vaccination on animal populations with high levels of natural immunity need to be investigated before costly campaigns are started.

Prevalence of leptospirosis in Belize

In a search for leptospirosis in Belize, at least one current case was diagnosed among 11 febrile hospital patients examined in a 2-week period in mid-1984. Sera from 440 survey subjects in 6 schools, 4 urban communities and 9 rural communities were examined for leptospiral antibodies by the microscopic agglutination test. 20 of 174 (11.5%) school pupils, 19 of 88 (22%) urban community subjects and 66/178 (37%) rural community subjects were positive at titres greater than or equal to 1:50, and 7.5%, 17% and 26%, respectively, were positive at greater than or equal to 1:100. Among all groups of survey subjects, serological reactions to antigens in the Australis serogroup predominated. Up to 81% of 155 sera from cattle in various areas of Belize were positive at titres greater than or equal to 1:100. Serological reactions to serogroup Sejroe predominated (43%), followed by Pyrogenes (16%) and Australis (15%). 20 of 71 (28%) pig sera were positive at greater than or equal to 1:100, predominantly to serovars in the Australis serogroup (51%). Of 162 sheep or goat sera examined, 65 (40%) were positive at greater than or equal to 1:100, mainly to serogroup Autumnalis (25%), followed by Australis (15%).

Leptospires in the marine toad (Bufo marinus) on Barbados

Leptospires were isolated from the kidneys of four of 211 toads (Bufo marinus) caught on Barbados. Two of the isolates were identified as Leptospira interrogans serovar bim in the Autumnalis serogroup (the most common cause of leptospiral illness on Barbados), and two as possibly new serovars in the Australis serogroup. Sera from 198 of the toads were examined by the leptospire microscopic agglutination test. Forty-two (21%) were positive at titers of greater than or equal to 1:100, and 54 (27%) at greater than or equal to 1:50. The predominating serogroups were Australis (50%), Autumnalis (23%) and Panama (13%). The agglutination tests on the culture-positive toads showed that serologic studies alone may be of limited value in these animals. Bufo marinus can harbor pathogenic leptospires, and it may be a significant source of the Autumnalis serogroup infections in the Caribbean.

The incidence of severe leptospirosis in Trinidad

Between February 1977 and September 1982, sera from febrile patients from all areas of Trinidad were examined for leptospiral agglutinins; 158 of 1714 patients (9%) were confirmed as current cases of leptospirosis (annual average 26 or 2.6 per 100,000 population). Of the remaining 1556 patients only 711 provided paired sera; 167 of these (23%) showed evidence of previous leptospiral infection. Of the 845 single samples, 125 were positive. The true incidence of the disease is probably much higher than reported here. Males comprised 74% of the current cases; their highest rate of infection was in the 30-39 year age group, the incidence in late teenage approaching this rate. For females, incidence increased with age up to late middle-age. The presumptive infecting serogroups most commonly recorded among the 158 current cases were Icterohaemorrhagiae (37%), Canicola (16%) and Autumnalis (11%). 13 of the cases died (case fatality rate, 8.2%).

Leptospires in vervet monkeys (Cercopithecus aethiops Sabaeus) on Barbados

Agglutinins to Leptospira were found at titers of greater than or equal to 1:100 in 150 of 501 (29.9%) vervet monkeys (Cercopithecus aethiops sabaeus) bled within 1 mo of capture in Barbados. Including a further 34 of 145 bled within 1 yr of capture, the seropositivity prevalence was 28.5%. A further 35 monkeys (5.4%) had traces of agglutinins or gave titers of 1:50. The proportion of seropositive adults (41.5%) was more than twice that of seropositive immature monkeys (17.6%). Among adults, 49.2% of males and 35.7% of females were seropositive, while among juveniles proportions of seropositive males and females were similar (17.8% and 17.4%, respectively). Seropositivity prevalences tended to increase in proportion to rainfall. In each of 165 of the 184 positive sera, a single serogroup predominated in the serological reactions. These serogroups were Ballum (61%), Icterohaemorrhagiae (16%), Autumnalis (15%), Pyrogenes, Panama, Pomona, Tarassovi and Canicola (8% altogether). In the other 19 positive sera no single serogroup predominated. Serial bleeding showed that vervet monkeys can retain naturally-acquired antibodies to Leptospira for at least 2.5 yr. The evidence suggests that vervet monkeys in Barbados are transmitting leptospiral infections among themselves independently of other groups of animals, and are not a major source of human leptospirosis.