Comparison between superficial and solid-state cultures of Isaria fumosorosea: conidial yields, quality and sensitivity to oxidant conditions

Abstract

Conidia production and quality from mycoinsecticides in solid-state cultures (SSC) are frequently inferred from superficial culture (SC) results. Both parameters were evaluated for two Isaria fumosorosea strains (ARSEF 3302 and CNRCB1), in SC and SSC, using culture media with the same chemical composition. For both strains, conidia production was higher in SC than SSC in terms of conidia per gram of dry substrate. Germination in both strains did not show significant differences between SC and SSC (>90 %). Similarly, conidia viability in ARSEF 3302 strain did not show differences at early stages between SC and SSC, but was higher in SC compared to SSC in the late stage of culture; in contrast, conidia from CNRCB1 strain did not differ between both culture systems. Some infectivity parameters improved in conidia from SSC, compared to SC at the early stages, but these differences disappeared at the final stage, independently of the strain. Both strains showed decreased conidia production when 26 % O2 pulses were applied; nevertheless, conidiation in SSC was two orders of magnitude more sensitive to oxidant pulses. In SC with 26 % O2 pulses, conidia viability for both strains at early stages, was higher than in normal atmospheric conditions. Infectivity towards Galleria mellonella larvae was similar between conidia from normal atmosphere and oxidant conditions; notably, for the strain ARSEF 3302 infectivity decreased at the final stage. This study shows the intrinsic differences between SC and SSC, which should be considered when using SC as a model to design production processes in SSC.

Forced Aeration Influence on the Production of Spores by Trichoderma strains

“…SSF is an aerobic process, therefore is highly needed an adequate oxygen diffusion through the fermented matter making one of the most important phenomena to support the microbial development [20]. Commonly a passive oxygen diffusion takes place in reactors such as flasks, trays or bags resulting in a high production of spores [14,16,21]. Arzumanov et al [22] reported that the aeration does not always make a big difference to increase the production of spores.…”

Improved conidiation from entomopathogenic fungi through 26% oxygen pulses in solid‐state culture depends on a balance between headspace volume and substrate amounts

“…All strains were maintained in Sabouraud agar plugs with 1 ml of sterile water at 4°C. Inocula were obtained by placing an agar plug in oat flour agar medium (Tlecuitl-Beristain et al 2010) and incubating for 10 days at 28°C with photoperiod of 12 h light and 12 h dark (Muñiz-Paredes et al 2016). Conidia were harvested using a magnetic stirrer with 20 ml of 0Á05% Tween 80.…”

“…Conidia were harvested using a magnetic stirrer with 20 ml of 0·05% Tween 80. Conidial suspensions were filtered through four layers of cheesecloth, and conidia production was determined using a Neubauer chamber (Muñiz‐Paredes et al ). Dilutions were done when necessary and 10 µl of the conidial suspension were loaded in each side of the chamber.…”

“…For example, Beauveria bassiana Bb 882·5 did not modify conidiation levels in oxygen‐enriched pulses (Garza‐López et al ). The previously mentioned I. fumosorosea strains were compared in terms of conidia production responses to oxygen‐enriched pulses in both SC and SSC (Muñiz‐Paredes et al ). In both systems, both strains decreased conidia production after application of oxygen‐enriched treatments.…”

“…However, the amount of nutrients was different, which affects the formation of biomass. Therefore, it was hypothesized that the biomass in each system, higher in SSC compared with SC cultures, may determine the oxygen consumption rate and the time that the oxygen‐enriched pulses remains and stimulates conidiation (Muñiz‐Paredes et al ).…”