Background: Endophytic fungi are known plant symbionts. They produce a variety of beneficial metabolites for plant growth and survival, as well as defend their hosts from attack of certain pathogens. Coastal dunes are nutrient deficient and offer harsh, saline environment for the existing flora and fauna. Endophytic fungi may play an important role in plant survival by enhancing nutrient uptake and producing growth-promoting metabolites such as gibberellins and auxins. We screened roots of Ixeris repenes (L.) A. Gray, a common dune plant, for the isolation of gibberellin secreting endophytic fungi. Results: We isolated 15 endophytic fungi from the roots of Ixeris repenes and screened them for growth promoting secondary metabolites. The fungal isolate IR-3-3 gave maximum plant growth when applied to waito-c rice and Atriplex gemelinii seedlings. Analysis of the culture filtrate of IR-3-3 showed the presence of physiologically active gibberellins, GA 1 , GA 3 , GA 4 and GA 7 (1.95 ng/ml, 3.83 ng/ml, 6.03 ng/ml and 2.35 ng/ml, respectively) along with other physiologically inactive GA5, GA9, GA12, GA15, GA19, GA20 and, GA24. The plant growth promotion and gibberellin producing capacity of IR-3-3 was much higher than the wild type Gibberella fujikuroi, which was taken as control during present study. GA5, a precursor of bioactive GA 3 was reported for the first time in fungi. The fungal isolate IR-3-3 was identified as a new strain of Penicillium citrinum (named as P. citrinum KACC43900) through phylogenetic analysis of 18S rDNA sequence. Conclusion: Isolation of new strain of Penicillium citrinum from the sand dune flora is interesting as information on the presence of Pencillium species in coastal sand dunes is limited. The plant growth promoting ability of this fungal strain may help in conservation and revegetation of the rapidly eroding sand dune flora. Penicillium citrinum is already known for producing mycotoxin citrinin and cellulose digesting enzymes like cellulase and endoglucanase, as well as xylulase. Gibberellins producing ability of this fungus and the discovery about the presence of GA5 will open new aspects of research and investigations.

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Plant growth promotion and Penicillium citrinum

Sequence breakpoints in the aflatoxin biosynthesis gene cluster and flanking regions in nonaflatoxigenic Aspergillus flavus isolates.

Distribution and toxigenicity of Aspergillus species isolated from maize kernels from three agro-ecological zones in Nigeria.

Encyclopedia of Food Microbiology.

Aspergillus niger is perhaps the most important fungus used in biotechnology, and is also one of the most commonly encountered fungi contaminating foods and feedstuffs, and occurring in soil and indoor environments. Many of its industrial applications have been given GRAS status (generally regarded as safe). However, A. niger has the potential to produce two groups of potentially carcinogenic mycotoxins: fumonisins and ochratoxins. In this study all available industrial and many non-industrial strains of A. niger (180 strains) as well as 228 strains from 17 related black Aspergillus species were examined for mycotoxin production. None of the related 17 species of black Aspergilli produced fumonisins. Fumonisins (B2, B4, and B6) were detected in 81% of A. niger, and ochratoxin A in 17%, while 10% of the strains produced both mycotoxins. Among the industrial strains the same ratios were 83%, 33% and 26% respectively. Some of the most frequently used strains in industry NRRL 337, 3112 and 3122 produced both toxins and several strains used for citric acid production were among the best producers of fumonisins in pure agar culture. Most strains used for other biotechnological processes also produced fumonisins. Strains optimized through random mutagenesis usually maintained their mycotoxin production capability. Toxigenic strains were also able to produce the toxins on media suggested for citric acid production with most of the toxins found in the biomass, thereby questioning the use of the remaining biomass as animal feed. In conclusion it is recommended to use strains of A. niger with inactive or inactivated gene clusters for fumonisins and ochratoxins, or to choose isolates for biotechnological uses in related non-toxigenic species such as A. tubingensis, A. brasiliensis, A vadensis or A. acidus, which neither produce fumonisins nor ochratoxins.

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Fumonisin and Ochratoxin Production in Industrial Aspergillus niger Strains

Variability of aflatoxin and cyclopiazonic acid production by Aspergillus section flavi from different substrates in Argentina.

Toxigenic fungi isolated from dried vine fruits in Argentina.

Influence of water activity on Penicillium citrinum growth and kinetics of citrinin accumulation in wheat

Influence of water activity and temperature on the growth of Wallemia sebi: application of a predictive model

The influence of water activity (aw) on deoxynivalenol accumulation in wheat at 25°C was studied. Gnotobiotic grains were conditioned at different aw levels, inoculated with a toxigenic Fusarium graminearum strain, and incubated for ten weeks. The highest accumulation of deoxynivalenol (1130 ug/kg) was detected at aw 0.980. At aw 0.945 and 0.925 the maximum quantities of toxin accumulated were 113 ug/kg and 93 ug/kg respectively. Deoxynivalenol was not detected in the substrate at aw 0.900. Results suggest that intermediate aw levels (0.97 – 0.92) are particularly critical at post harvest time because those are conditions under which deoxynivalenol production is most likely to be initiated naturally.

Ricardo Comerio

Papers

Variability of aflatoxin and cyclopiazonic acid production by Aspergillus section flavi from different substrates in Argentina.

Toxigenic fungi isolated from dried vine fruits in Argentina.

Influence of water activity on Penicillium citrinum growth and kinetics of citrinin accumulation in wheat

Influence of water activity and temperature on the growth of Wallemia sebi: application of a predictive model

Influence of water activity on deoxynivalenol accumulation in wheat